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Argos
2010-Aug-24, 04:44 PM
Throughout geological time, patterns of global diversity of tetrapod families show 97 per cent correlation with ecological modes. Global taxonomic and ecological diversity of this group correlates closely with the dominant classes of tetrapods (amphibians in the Palaeozoic, reptiles in the Mesozoic, birds and mammals in the Cenozoic). These groups have driven ecological diversity by expansion and contraction of occupied ecospace, rather than by direct competition

Bold mine. Some claim, eh?

Link (http://rsbl.royalsocietypublishing.org/content/6/4/544.abstract).

Ken G
2010-Aug-24, 10:20 PM
I guess I'm not clear on why "expanding the occupied ecospace" is something different from "direct competition." If I'm a reptile and some mammal is invading my turf, I'm feeling like I'm in competition with them. Do you get what distinction they are drawing there?

evo4ever
2010-Aug-24, 10:51 PM
I think the point here is which is the main driver. If we take the reptile example. If there are mammals around but it takes a change in the eco space for mammals to dominate then eco space is the main driver. If however the eco space stays constant and mammals invade and succeed then competition is dominant. Hope this helps explain science. As to which one is the the better thoery... god knows ;)

grant hutchison
2010-Aug-24, 10:57 PM
I think the claim is that these animals increased their taxonomic diversity mainly by finding new ways of living, rather than competing with other animals for existing ways of living. They went around the competition, ecologically, rather than "battling for dominance" in the competition's existing ecological niche.

Grant Hutchison

Luckmeister
2010-Aug-25, 12:43 AM
So they're saying, on an earlier (less crowded) Earth, expanding a species' territory drove diversity more than competing for territory? Well......yeah. Doesn't that sorta figure without needing a big study on it.....or am I missing something? :think:

Mike

Ken G
2010-Aug-25, 02:55 AM
I think the claim is that these animals increased their taxonomic diversity mainly by finding new ways of living, rather than competing with other animals for existing ways of living. They went around the competition, ecologically, rather than "battling for dominance" in the competition's existing ecological niche.That does seem to be what they are saying, but I would point out that if one species wins the battle for dominance hands down, it would show up in the fossil record as no battle at all. When is "competition" too one-sided to count? It probably relates to how rapidly the adaptations appear-- if they have to move slowly into a new niche, then the result might look more like a competition, but if they can "jump" into a new niche with a sudden adaptation, then it might look like "first come, first serve." I'm not sure what the current thinking is on how rapid or how gradual this kind of diversity appears.

Argos
2010-Aug-25, 01:51 PM
So they're saying, on an earlier (less crowded) Earth, expanding a species' territory drove diversity more than competing for territory?

Well, they include the Cenozoic period, which is the one we´re living in. So, that mechanism would be working even today.

Ken G
2010-Aug-25, 02:29 PM
I guess another key issue is how much more difficult is competition when one species is already "in place" in the niche.

boom stick
2010-Aug-25, 02:34 PM
IIRC, the scientific consensus has been for some time that successful reproduction is a much more important factor in evolution than direct competition between species, as is often misinterpreted from the phrase 'survival of the fittest'. At least according to my middle school biology text book (around 10 years ago). This study seems to support that and its conclusions are, in my opinion, very logical and mainstream.

Ken G
2010-Aug-25, 03:58 PM
IIRC, the scientific consensus has been for some time that successful reproduction is a much more important factor in evolution than direct competition between species, as is often misinterpreted from the phrase 'survival of the fittest'. At least according to my middle school biology text book (around 10 years ago). This study seems to support that and its conclusions are, in my opinion, very logical and mainstream.So they might be equating "direct competition" with "out-surviving" rather than "out-reproducing." To me, either one is a clear example of direct competition, because if you out-reproduce, you will generate a larger population, which will compete for resources, thereby limiting the population size of the competing species. Smaller population sizes then are more vulnerable to extinction-- that seems like a pretty direct form of competition to me!

peledre
2010-Aug-25, 04:24 PM
While opening up previous unoccupied ecosystems can be a tremendous advantage (like life on land for the first time) it still seems to me that competition for limited resources is the primary driver of adaptation.

Our utilization of space and the resources available there will provide us a terrific advantage, one that would make our species much more fit for survival.

grant hutchison
2010-Aug-25, 04:25 PM
So they might be equating "direct competition" with "out-surviving" rather than "out-reproducing." To me, either one is a clear example of direct competition, because if you out-reproduce, you will generate a larger population, which will compete for resources, thereby limiting the population size of the competing species. Smaller population sizes then are more vulnerable to extinction-- that seems like a pretty direct form of competition to me!You won't limit the population size of competing species if you're the first into a new niche: you'll have no competition right up until you hit the carrying capacity of the niche. I think that's what the authors mean by "expansion and contraction of occupied ecospace, rather than by direct competition": you can only "expand occupied ecospace" by occupying a previously unoccupied niche.

Grant Hutchison

Ken G
2010-Aug-25, 04:32 PM
You won't limit the population size of competing species if you're the first into a new niche: you'll have no competition until you hit the carrying capacity of the niche. I think that's what the authors mean by "expansion and contraction of occupied ecospace, rather than by direct competition": you can only "expand occupied ecospace" by occupying a previously unoccupied niche.
Right, but if that process happens gradually, it is natural to expect some competition along the way. So I'm not clear about this clear distinction that they are trying to draw. It seems to me that in order to make such a distinction, you need two things: rapid adaptation, and a sense to which trying to enter a niche that is "already full" does not count as "competition" in that niche-- perhaps because competing for entry into an already full niche is a different proposition than simply competing in a niche where both species are already present, or one where both species are still in a growth phase. But when they opened the Panama canal, species from the two oceans entered already "full" niches in the other oceans-- and in some cases outcompeted the natives quite effectively. What is a "full niche" anyway?

In other words, it seems to me that "ecospace contraction" and "direct competition" are simply names for two processes that are always going to be going on, and the net biodiversity is an outcome of both. To say which dominates, you need to be able to separate them more than I can see being possible. When the Panama canal got opened and lamprey eels came over, were those eels "contracting the ecospace" of the natives, or "competing" with them? While the mammals were taking over the Earth from the reptiles, didn't they have to compete with them?

grant hutchison
2010-Aug-25, 04:37 PM
And likewise when the Panama landbridge formed, and land species mixed north and south.
But the authors seem to be suggesting that such "out-competition" events are rare compared to "new niche" events. Which I think is why Argos is surprised.

Grant Hutchison

Argos
2010-Aug-25, 04:39 PM
Well, indeed. :)

boom stick
2010-Aug-25, 04:47 PM
So they might be equating "direct competition" with "out-surviving" rather than "out-reproducing." To me, either one is a clear example of direct competition, because if you out-reproduce, you will generate a larger population, which will compete for resources, thereby limiting the population size of the competing species. Smaller population sizes then are more vulnerable to extinction-- that seems like a pretty direct form of competition to me!
I agree that both "out-surviving" and "out-reproducing" can be considered forms of direct competition, just making the point that the latter one is perhaps considered more important nowadays. For me, direct competition is simply competition for the same resources in the same niche in a zero-sum kind of fashion.

Ken G
2010-Aug-25, 04:50 PM
The problem is seen from the fact that Argos has expressed surprise, while others have expressed the opposite opinion, like their conclusions are obvious. I'm suggesting the culprit is the very idea that "out-competition" events are fundamentally different from "new niche" events in the first place. It's not obvious that when a "new niche" appears, the ultimate population that dominates that niche is determined by whoever got their first, and if it isn't, then we are seeing an example of direct competition.

Fazor
2010-Aug-25, 06:15 PM
I just read about this in the Huffington Post's article (here (http://www.huffingtonpost.com/2010/08/24/darwin-wrong-evolution_n_692502.html)). Whether or not it's "surprising", or even actually in opposition to Darwin's opinion, probably is a mater of interpretation.

If a species suddenly moves into "unoccupied space" (such as the bird learning to take flight, as mentioned in the Huffington Post article), reproduction booms. Evolution booms. Is that a surprise? Well, since evolution is a process that occurs through successive breeding, doesn't it make since that the more a species breeds, the greater the chances and faster the evidence of evolution will arise?

But remember, "survival of the fittest", or competition based evolution, doesn't just mean competition between competing species. If a mutation gives rise to a reproductive or survival based advantage of one individual over the others of it's own species, that's competition among the single species. And as I understand the theory (fair at this point to note I'm only about a third of the way through 'On the Origin'), it's this competition that really drives evolution. A mutation giving rise to some advantage isn't necessary for said mutation to persist and lead to the evolution of a new species. But advantages that arise are going to more often leave to persistence in the mutation.

Thus I would say (but what do I know?) that "occupation of space" really just leads to a population boom as the species takes advantage of an abundance of resources. The evolution itself is still largely a product of inter-species and intra-species competition. Which in my opinion means that space can lead to optimal conditions for, but doesn't in and of itself cause, evolution.

Ken G
2010-Aug-25, 08:24 PM
This doesn't sound like what the authors are talking about, but a distinction I could see making, and calling it the difference between expansion of ecospace versus competition, is to ask: does biodiversity undergo big changes because "a new player" appears in the gene pool, which outcompetes the existing lifeforms (whether different species or the same species) in regard to the existing environment, or whether a change in the environment appears, which then selects whichever species or individuals are already best adapted to it? If the latter, then we just have a reproductive free-for-all, which will set the new biodiversity without any competition (either between species or within one species). That sounds more like what Fazor is saying. But if we are talking about a change in the gene pool which then expands within some existing environmental niche, then it is going to have to compete to do so. Even birds have to land, and they have to eat, so perhaps that does support Fazor's claim that we shouldn't call it evolution without the competition in there.

What's more, even if we start out with a change in environment that selects some existing genome, which we might not call competition because there may not yet be any species that have evolved to an equilibrium with the new environment, it can't be long before they will reach equilibrium, and that equilibrium must then in turn evolve in response to competition. Isn't it possible that one species might have a faster reproductive rate, so quickly expand to respond to some new environmental conditions that support a higher population in that species, but then another species, or subgroup within that species, with a slower reproductive rate but with competitive advantages, will displace them on their own reproductive timescale? So I'm not sure there is really any such thing as a full niche, or a concept of "ecospace," that can get away with ignoring competition or be explanatory by itself of a given set of biodiversity.

Fazor
2010-Aug-25, 08:46 PM
I don't have access to the paper itself, only the article in the Huffington Post. (Unless I'm mistaken, which is always a possibility, to view the paper as linked in the OP one needs either a subscription, or needs to buy one-time access to the particular paper.) Did you read the article I linked? I'm just curious if they're not reporting it correctly, or if I'm missing something. They way I take the news article, the "findings" are that evolution is primarily driven by available living space (defined as a species access to things such as food and habitat etc.) And I argue that it's not driven by, but rather aides, the evolutionary process, but said process is still driven by competition.

Ken G
2010-Aug-25, 09:21 PM
I did read the paper, which is short and includes this kind of clarification:

The exponential increase from one species to many tens of thousands occupying a great variety of ecological modes could have been driven by either (i) the expansion of habitats occupied as tetrapods moved from the waterside to exploit new sectors of Earth’s
surface, such as forests, plains and deserts, or (ii) competition within a more-or-less constant amount of habitat, leading to specialization within communities so that more species live together, with each exploiting an ever-narrower range of resources.
To me, that means the environment they are imagining is pretty much the same, but a new adaptation allows what is initially a single species to have access to it, which precipitates a population explosion. Then, new adaptations appear, in that same environment, which allows new access, etc. So framed like that, it doesn't sound like there's any competition. My problem with it is that, first of all adaptations don't appear all at once, they should appear as a result of competition in regard to the new access. In other words, competition, and access to new ecospace, are not independent things that can be separated. What they apparently mean by "competition" is strictly that between different populations, where new adaptations appear and begin to take better advantage of resources that we already there. But that sounds like birds developing the ability to fly, why is that something different than competition to take advantage of the environment? Why do we have to say that birds opened new "ecospace" when they developed the ability to fly, rather than just saying they "outcompeted" everyone else, including their own original species, in how they take advantage of air? They still eat the same things, they still predate or avoid predation, as do the competing lifeforms. So I'm not saying they are stressing the wrong one of (i) and (ii) above, I'm saying I'm not convinced any such fundamental distinction exists, it just sounds like a non-equilibrium and equilibrium phases of a very ongoing process that has to both be going on. It's like the question, is the Sun hot because of gravity or nuclear fusion? Well, you needed gravity to get it hot, and you need fusion to keep it at the temperature it is at, so you just can't tell the story without both.

Their conclusions seem to stem from this key result:

The global taxonomic diversity of tetrapod families correlates strongly with the number of ecological modes they occupied through time...
In other words, they enumerated the diversity, and identified what they considered to be the number of different "modes" (3 sizes, 16 diets, and 6 habitats, in combination) they occupied. It seems they wish to conclude that the increased access to modes was the causal agent to explaining the increase in diversity, but they don't address how competition in the form of a "race to adapt" did not enter into the filling of more modes, nor how competition within the "filled" modes might have affected the "taxa per mode" issue.

Ken G
2010-Aug-25, 10:03 PM
Here's another key snippet:

Though the tetrapod record does not provide evidence for direct competition, there is evidence of competition in the manner of incumbent replacement, in which established groups can exclude competitors, even if those competitors possess advantageous key adaptations, until the incumbents are removed from their foothold by a major environmental disruption such as a mass extinction, at which time the key adaptations of the invading clade allows them to colonize the area before the incumbents can reestablish themselves (Rosenzweig & McCord 1991). The data support the growing evidence that, except following mass extinctions, tetrapod diversity was primarily achieved by unrestricted expansion into empty ecospace, that is by the filling of unrealized modes of life, and multiplying into already realized modes.In other words, competition doesn't increase biodiversity, but it can limit it.

HenrikOlsen
2010-Aug-25, 10:50 PM
But remember, "survival of the fittest", or competition based evolution, doesn't just mean competition between competing species.
And this is one of my main beefs with the "survival of the fittest" thing, drop the "just".

Evolution isn't about competition between species, it's about competition between individuals of the same species.
When a baby birdie falls out of a nest and is eaten by a cat, evolution isn't happening because the cat survived, it's happening because the sibling which pushed it out, or didn't crawl around, or was better at hanging on in the wind, survived.
Ok, it's also happening because the cat survive, but that's because it is better than its siblings at finding baby birdies to eat.

The competition between species does have a role, but that role is to define the playing field on which the individuals are competing.

Speciation within a constant environment happens when two groups pick slightly different ways of using the resources which result in lessened competition between those two groups when that combines with sexual signals that allow them to have a preference when breeding.

Fazor
2010-Aug-26, 12:13 AM
@ Henrick; that's a good point. Even a mutation or divergence that allows an edge of one individual of a species to better survive predation of another species, improves the ability to prey on a food source, etc, is really improving the chance said diversion will be sustained because it (the individual and its offspring) has an advantage over all other members of the same species. I'll agree to drop the "just".

Fazor
2010-Aug-26, 12:29 AM
@Ken; okay I think I got the basics of the paper now. Evolution to expand into new environments, NOT because it gave them an advantage, but because it gave them an ability to utilize previously unused "space".

And if that's what is being argued, I think I agree with you. The population in the new mode "explodes" because it is not sharing resources. So i'd have to ask; could the new species have reproduced so prolifically under the previous environment? Well then doesn't that mean the new species' gained an advantage? Which, as you say, means it out-competed the prior species?

Ken G
2010-Aug-26, 03:51 AM
Perhaps a particular problem here is that the article is not really about the size of populations, it is about the number of families (those are groups of similar species), regardless of population size. So noting that a particular family can have a population explosion doesn't directly affect their results. They might be arguing that a larger population within one family gives it more chances to find new adaptations and generate new families of species, or they might be arguing that higher populations are more extinction-proof, so reduces the loss of families moreso than the creation rate of new ones. Unfortunately, they don't say-- they merely find a correlation between ecological "modes" (size, diet, and habitats that are represented by the families at any given time) and number of families represented across all those modes. Indeed, they find that each mode can support roughly the same number of families, so when the number of families increases, it is generally because the number of modes represented increases.

What's not clear is if they have the direction of the causality correct-- they don't seem to rule out the possibility that if you get more families, for whatever reason, it is likely that they will express a larger number of ecological modes. In other words, did the family appear because the mode was "available", or did the family just appear for some other reason, perhaps a purely random one, and then it had a higher chance of surviving if it found a less occupied "mode."

If so, it's the new mode that allowed the new family to thrive, but it's still competition that prevented an even larger number of families to appear. So that would still mean the story is one of both competition and finding greener pastures, as key agents in the evolutionary process. It may not be appropriate to pit one against the other and ask which one "dominates" the determination of the number of families you are going to have. But it does support the idea that time does not give you more families in each mode, so much as it gives you more modes. If so, it is because of competition that you need a new mode to increase the number of families. It seems that competition is playing a key role, but not as a means for generating an increase in biodiversity, rather as a damping on biodiversity that must be circumvented via ecospace expansion. So we may just have been misinterpreting the point they were making.

(By the way, for those who haven't seen the article, one interesting point they make that I had not appreciated is that barring various violent extinction events, the number of families of "tetrapods", basically animals with bones and four appendages, so that includes birds, has increased very steadily with time, and so has their variety of size, diet, and habitat, yet there still seems to be a majority of sizes, diets, and habitats that one could imagine that are not yet occupied by any tetrapod. They conclude that if not for humans taking over a large share of the world's ecological resources, this process might have continued for many millions of years, resulting in substantially more diversified tetrapods than we have even now. Dinosaur tetrapods were far less diverse, in terms of the number of families represented at any given time, even though it seems like there were an awful lot of different kinds of dinosaurs.)

Finally, I wonder what has been happening to the average number of species per family over this same timeframe? Is the process that gives us new families any different from the process that gives us new species?

transreality
2010-Aug-26, 04:05 AM
The processes that determine numbers of individuals per species are very different to those that determine number of speciation events. However beyond that, it is quite likely that the use of the family level is due to taxonomic resolution rather than any evolutionary effect. That is, uncertainty about species identifications, and their probability of recovery will vary with age, however the identification of the presence of a family level taxon would be more robust.

Ken G
2010-Aug-26, 04:11 AM
So i'd have to ask; could the new species have reproduced so prolifically under the previous environment? Well then doesn't that mean the new species' gained an advantage? Which, as you say, means it out-competed the prior species?I think they are using a very specific meaning for "direct competition." They are focusing the competition on the resources within a particular ecological mode, not between families. In other words, they don't say "family A competes with family B to survive", they say there is competition only if they are shooting for the same resources.

Fazor
2010-Aug-26, 01:47 PM
I think they are using a very specific meaning for "direct competition." They are focusing the competition on the resources within a particular ecological mode, not between families. In other words, they don't say "family A competes with family B to survive", they say there is competition only if they are shooting for the same resources.

I'd argue that moving to a new, unoccupied or available "mode" is the same thing as out-competing those under the original mode. Further when you consider all the possible evolutionary events that don't take. Though I'm not sure I can explain that thought in a way that makes sense to anyone but me.

Now I can agree with the argument that a mutation that results in an advantage doesn't always ensure the emergence or prosperity of the organism. So in the strictest sense, if they want to argue "survival of the fittest" isn't an iron-clad-always-truth, then fine. I don't think Darwin himself would argue against it.

Anyway, I'm sure it's clear that I'm well beyond my comprehension of such matters -- the way I'm using terms makes me feel like an ATM proponent that's decided to make up my own definitions for already established words. But there's been some interesting discussion here that will definitely weigh in as I continue to read and study Darwin's works. (In an amateur capacity, of course.)

Ken G
2010-Aug-26, 09:01 PM
I'd argue that moving to a new, unoccupied or available "mode" is the same thing as out-competing those under the original mode. I agree that would be a colloquial use of "compete", but it now appears that the authors don't take that meaning.

Now I can agree with the argument that a mutation that results in an advantage doesn't always ensure the emergence or prosperity of the organism. So in the strictest sense, if they want to argue "survival of the fittest" isn't an iron-clad-always-truth, then fine. I don't think Darwin himself would argue against it. Yes, that's an interesting point-- the authors state there is good reason to think that a species that is already in some sense ingrained in a particular mode can resist invasion by another species or family, even if that other species is "more fit"-- as evidenced by the fact that after a die-off event, the new species moves into the reopened space, out-competing the previous species in a way they could not do with the other species ingrained into the niche. I don't know what evidence they have for that, but it's certainly not the standard view of competition that gets taught in high school biology.

Fazor
2010-Aug-26, 09:10 PM
I agree that would be a colloquial use of "compete", but it now appears that the authors don't take that meaning.
Yes, that's an interesting point-- the authors state there is good reason to think that a species that is already in some sense ingrained in a particular mode can resist invasion by another species or family, even if that other species is "more fit"-- as evidenced by the fact that after a die-off event, the new species moves into the reopened space, out-competing the previous species in a way they could not do with the other species ingrained into the niche.

Perhaps it's a problem with our view of 'more fit'; as in order for a change to occur, reproduction must be involved. If, for whatever reason, the new species can't get a foothold in that area, then it won't survive.

Lets call it "Last man on earth" syndrome; as a human, I could be born with bullet proof skin and doubly-sized muscles, meaning I could much better fight off any male competing for the female of my desire. That doesn't mean said female would want to reproduce with a man that looks more like a bipedal armadillo than a "normal" human male. There may be no good reason for her not to want to, other than she doesn't find it attractive.

Suddenly, there's a die-off event, and there's much fewer males to chose from. I'm now, figuratively, "the last man on earth". Said female may be a little more willing to procreate.

. . . just thinking out loud.

HenrikOlsen
2010-Aug-26, 09:15 PM
Part of the problem of getting to different mode of doing things is that some of the intermediate steps needed can be detrimental compared to the "old" way and therefore just won't survive long enough to breed in stable ecologies.

Part of the diversity explosion following massive die-backs may be because, in an expanding population, even selected-against traits can increase in absolute number of individuals carrying them, so there are more traits lasting for longer in more individuals, thus making for the opportunity for the slightly "worse" intermediate forms to survive enough to breed enough to take the next steps to new niches.

Ara Pacis
2010-Aug-26, 10:10 PM
I agree that would be a colloquial use of "compete", but it now appears that the authors don't take that meaning.
Yes, that's an interesting point-- the authors state there is good reason to think that a species that is already in some sense ingrained in a particular mode can resist invasion by another species or family, even if that other species is "more fit"-- as evidenced by the fact that after a die-off event, the new species moves into the reopened space, out-competing the previous species in a way they could not do with the other species ingrained into the niche. I don't know what evidence they have for that, but it's certainly not the standard view of competition that gets taught in high school biology.

I'm thinking of an example where plants may have a root system so compact that other root systems can't penetrate into the soil to gain a foothold. However, a flood, fire, or impact, could stir up the soil in a manner that makes colonization of that disturbed area anyone's game. Another example, if all the nesting areas for a particular size and locomotive type of animal is taken, then even an over-abundance of food might not allow similarly sized and locomotive animal to stay and enjoy the food and set up house and multiply before it dies of exposure or predation.

I generally disagree with the concept of a "race to adapt". Whether adaptations are caused by random mutations or the new utilization of vestigial DNA, a race supposes a mindset towards a goal, and we all know that evolution has neither mind nor goal. Competition means struggling for the same resource, not a new resource. Think less of space as volume and think in more dimensions. If a plant mutates (or otherwise adapts to different conditions) and starts growing a new type of fruit, then an animal that has either the current ability or adapts a new ability to eat that fruit can be said to be expanding into the new "foodspace", but animals that ate other fruits cannot be said to be in competition for that new foodstuff, even if they previously were in competition for a different foodstuff. We might then look at other factors to see if physical space for transportation throughways or shelter are in competition too, but I suspect food is the main driver.

caveman1917
2010-Aug-27, 02:35 AM
If a regrowth after an extinction event can be likened to a situation with unlimited resources, wouldn't it be natural for there to be no selective pressure?
When the mutation rate is held constant, a given population would produce some average number of mutations. Since mutations are selected against, this means the number of mutations contributing to the next population (and thus number of speciation events) maximises in this scenario. It seems to be saying that evolution doesn't apply when there is no selective pressure, but that doesn't seem to be such a big claim.

caveman1917
2010-Aug-27, 02:58 AM
Yes, that's an interesting point-- the authors state there is good reason to think that a species that is already in some sense ingrained in a particular mode can resist invasion by another species or family, even if that other species is "more fit"-- as evidenced by the fact that after a die-off event, the new species moves into the reopened space, out-competing the previous species in a way they could not do with the other species ingrained into the niche. I don't know what evidence they have for that, but it's certainly not the standard view of competition that gets taught in high school biology.

But the niche has changed. After the extinction event, a property such as "speed of resource acquisition" could become relevant, so the fitness would be defined differently - if at all. One can't really compare the fitness before and after, the definition of it has changed.

Ken G
2010-Aug-27, 03:40 AM
Suddenly, there's a die-off event, and there's much fewer males to chose from. I'm now, figuratively, "the last man on earth". Said female may be a little more willing to procreate.That would be an example of the same species evolving in a new direction, or a new species breaking off from an old one. Those might certainly be relevant parts of evolution, they're just not what these authors see as the key issue for biodiversity. They seem to see the key issue as being that competition limits biodiversity (there's only "room" for a few families per mode), until an adaptation of some kind opens up new ecospatial modes-- and then it's open field running to new biodiversity. I think what you're saying is that this may overlook the role competition plays in assisting the appearance of that new adaptation, which resonates with some things said earlier and what Henrik Olsen just said. Competition and ecospace may be two elements of the same story.

Ken G
2010-Aug-27, 03:43 AM
Part of the diversity explosion following massive die-backs may be because, in an expanding population, even selected-against traits can increase in absolute number of individuals carrying them, so there are more traits lasting for longer in more individuals, thus making for the opportunity for the slightly "worse" intermediate forms to survive enough to breed enough to take the next steps to new niches.In that case, the authors should not deal so lightly with the die-backs (they tend to use language like "except for a few periods of die-offs, the number of families has increased exponentially." If their core argument is right, that biodiversity increases when families get access to new modes (presumably by evolving new species), they might want to look at an important role being played by those die-backs in creating access to those new modes, ironically.

Ken G
2010-Aug-27, 04:08 AM
I'm thinking of an example where plants may have a root system so compact that other root systems can't penetrate into the soil to gain a foothold. However, a flood, fire, or impact, could stir up the soil in a manner that makes colonization of that disturbed area anyone's game. Another example, if all the nesting areas for a particular size and locomotive type of animal is taken, then even an over-abundance of food might not allow similarly sized and locomotive animal to stay and enjoy the food and set up house and multiply before it dies of exposure or predation.Yes, I think those are the kinds of scenarios the authors must be talking about as well, in terms of the difficulty in breaking into previously occupied ecospace. If so, it does seem like the normal evolutionary tale should be modified substantially-- instead of saying you have a full niche, but some adaptation allows a new species to evolve by outcompeting what is already there, we might want to say that adaptations allow access to pristine ecospace, but those adaptations might get their start either in outcompeting the same species, or that die-offs might allow wide open ecospace which then promotes adaptations into new ecospaces in the ensuing "free-for-all". Those sound like a kind of mixture of competition and ecospace issues, but certainly not just "survival of the fittest" all by itself.


I generally disagree with the concept of a "race to adapt". Whether adaptations are caused by random mutations or the new utilization of vestigial DNA, a race supposes a mindset towards a goal, and we all know that evolution has neither mind nor goal. I don't see the race metaphor as requiring a mindset-- instead, I see it as an issue of there being a need for speed. In other words, if a pristine ecospace is available, and if several species make progress toward utilizing it, the one that does so the fastest may well be the ultimate winner-- where "winning" is a metaphor for generating biodiversity.


Competition means struggling for the same resource, not a new resource.That's very much how the authors are using the term, but it's pretty restrictive-- if the thesis is that pristine ecospace promotes biodiversity, then there is a competition to take advantage of it. People who say that birds are dinosaurs are saying that dinosaurs avoided extinction by finding new modes, but you should be able to track which dinosaur species were responsible for that expansion-- and which ones got "outcompeted" for the new niche, essentially by being too slow to get there. But that's apparently not what is meant by "direct competition."


Think less of space as volume and think in more dimensions. If a plant mutates (or otherwise adapts to different conditions) and starts growing a new type of fruit, then an animal that has either the current ability or adapts a new ability to eat that fruit can be said to be expanding into the new "foodspace", but animals that ate other fruits cannot be said to be in competition for that new foodstuff, even if they previously were in competition for a different foodstuff.Imagine that a bunch of different species can eat that new fruit, but cannot digest it very well. Whichever species gets an adaptation first that allows them to digest it better will benefit from that new foodstuff. But the adaptation might not appear suddenly, and many species might begin to see adaptations that can better digest that new foodstuff. So they are in competition-- the group that develops the adaptation far enough to take advantage of that fruit might experience a population explosion, which then reduces the availability of that fruit, which then removes the evolutionary pressure on the other species to complete that adaptation. They have been "outcompeted" for the new ecospace.


We might then look at other factors to see if physical space for transportation throughways or shelter are in competition too, but I suspect food is the main driver.The paper looked at three modes-- size, habitat, and food. I'm not sure why just habitat and food didn't suffice, but perhaps the issue is with predation-- a small creature might avoid predators by adapting into larger size, at which point they are in a new mode because their previous predator is gone. There seems to be some oversimplification involved in the mode counting.

Ken G
2010-Aug-27, 04:11 AM
It seems to be saying that evolution doesn't apply when there is no selective pressure, but that doesn't seem to be such a big claim.
Yet Henrik Olsen gave an example of a situation where evolution is stimulated when there is no selective pressure-- because the absence of selection pressure allows a species to adapt "past" a bottleneck. I imagine he had in mind scenarios like, where having feathers on your arms might be nice for cooling you or some such thing, but too many feathers is a downright hindrance that would be selected against in a competitive environment. But in an environment of plenty, with few selection pressures and rapid growth, it might not matter to have those extra feathers-- and then even more feathers might appear, which could be wings.

Ken G
2010-Aug-27, 04:17 AM
But the niche has changed. After the extinction event, a property such as "speed of resource acquisition" could become relevant, so the fitness would be defined differently - if at all. One can't really compare the fitness before and after, the definition of it has changed.I agree-- that's why it seems to me that a combination of competition and ecospace issues will always be relevant. If the ecospace is full, competition determines who survives and who goes extinct. If an ecospace is more empty, competition determines who fills it fastest. The authors are not really talking about evolution writ large, they are just talking about generation of biodiversity. They don't care if 100 species go extinct and 200 new ones appear, or if none go extinct and 100 more appear, that's the same biodiversity to them. So they are in a sense blind to competition within a full niche, they just care about what causes biodiversity, and they narrowly define "direct competition" in a way to make it not so relevant except as a limitation on biodiversity that needs new ecospace to circumvent.

Ara Pacis
2010-Aug-27, 04:28 AM
I don't see the race metaphor as requiring a mindset-- instead, I see it as an issue of there being a need for speed. In other words, if a pristine ecospace is available, and if several species make progress toward utilizing it, the one that does so the fastest may well be the ultimate winner-- where "winning" is a metaphor for generating biodiversity.
That's very much how the authors are using the term, but it's pretty restrictive-- if the thesis is that pristine ecospace promotes biodiversity, then there is a competition to take advantage of it. People who say that birds are dinosaurs are saying that dinosaurs avoided extinction by finding new modes, but you should be able to track which dinosaur species were responsible for that expansion-- and which ones got "outcompeted" for the new niche, essentially by being too slow to get there. But that's apparently not what is meant by "direct competition."

Imagine that a bunch of different species can eat that new fruit, but cannot digest it very well. Whichever species gets an adaptation first that allows them to digest it better will benefit from that new foodstuff. But the adaptation might not appear suddenly, and many species might begin to see adaptations that can better digest that new foodstuff. So they are in competition-- the group that develops the adaptation far enough to take advantage of that fruit might experience a population explosion, which then reduces the availability of that fruit, which then removes the evolutionary pressure on the other species to complete that adaptation. They have been "outcompeted" for the new ecospace.Possibly, there can happen to be multiple organisms that may adapt to eat a new foodstuff, but I don't think it's a necessary or even a scientific assumption. The phrase, "nature abhors a vacuum" would seem to fit here, which is appropriate because it can reveal the animist mindset with which some people imbue the process of evolution. Foodstuffs can go uneaten by animals that might conceivably compete for it. Even in a pristine wilderness, food often rots on the vine, and while it is consumed eventually, by bacteria or fungi or insects, the various birds just weren't in that much of a competition to eat every last available scrap of food. Humans produce waste plastic, but I don't see any animals in a race to use that for a foodstuff either: it's an empty niche.

I agree with a lot of your points, however, we may define competition differently. If there is enough to go share, then I don't see any actual competition. It is only when losing the competition has deleterious effects upon the population's ability to survive that I think it arises to survival of the fittest, otherwise it's survival of the good enough.

HenrikOlsen
2010-Aug-27, 04:41 AM
Yet Henrik Olsen gave an example of a situation where evolution is stimulated when there is no selective pressure-- because the absence of selection pressure allows a species to adapt "past" a bottleneck. I imagine he had in mind scenarios like, where having feathers on your arms might be nice for cooling you or some such thing, but too many feathers is a downright hindrance that would be selected against in a competitive environment.
Except that feathers is a bad example, since they're great for insulation, not cooling, and since they are easy to modify compared to e.g. bone structure they're ideal for developing markers for sexual selection.
With bones, the ceratopsidae and, with feathers, the peacock, the pheasant and the birds-of-paradise, shows that sexual dimorphism can push the development of even quite severe handicaps on males because of competition (actually two distinct competitions, one within the females and one within the males, with the two competitions intertwining do drive co-evolving in a direction distinctly disadvantageous for the survival of the males).

BTW, I see that I may have misread some of the intent of the authors referenced in the OP.
I suspect they're talking about the phase space of all possible organisms, and the development of traits to occupy niches not previously occupied is definitely part of expansion within that phase space, even without physical expansion of living space and thus not needing die-offs to make room for expansion.

Ken G
2010-Aug-27, 04:46 AM
Possibly, there can happen to be multiple organisms that may adapt to eat a new foodstuff, but I don't think it's a necessary or even a scientific assumption.If the adaptation rates are vastly different, you would never even know the other species had that capacity, as its evolutionary pressure will be removed before the adaptation can occur. But had the niche remained open indefinitely, they might have eventually entered that niche-- we wouldn't know. Yet that's a race lost.


Foodstuffs can go uneaten by animals that might conceivably compete for it. Even in a pristine wilderness, food often rots on the vine, and while it is consumed eventually, by bacteria or fungi or insects, the various birds just weren't in that much of a competition to eat every last available scrap of food. That's very true, but it doesn't mean they aren't competing for that same foodstuff elsewhere. It just means that competition is not completely efficient.

Humans produce waste plastic, but I don't see any animals in a race to use that for a foodstuff either: it's an empty niche. There hasn't been a whole lot of time there-- if we make plastic for a million years, we may find critters adapting to eat it. Microbes probably already are.


I agree with a lot of your points, however, we may define competition differently. If there is enough to go share, then I don't see any actual competition. It is only when losing the competition has deleterious effects upon the population's ability to survive that I think it arises to survival of the fittest, otherwise it's survival of the good enough.I agree that competition looks very different in a period of population expansion-- then the winner is the one with the fastest rate of taking advantage of the new ecospace, not the one "most fit" for that ecospace. It's a different type of "fit", and a different type of "competition," but it's all in the spirit of populations controlled by selection pressures of various types.

Ken G
2010-Aug-27, 05:00 AM
Except that feathers is a bad example, since they're great for insulation, not cooling, and since they are easy to modify compared to e.g. bone structure they're ideal for developing markers for sexual selection.Perhaps so, just an illustrative rather than serious example.

With bones, the ceratopsidae and, with feathers, the birds-of-paradise and peacocks shows that sexual dimorphism can push the development of even quite severe handicaps on males because of competition (actually two distinct competitions, one within the females and one within the males, with the two groups co-evolving in a direction distinctly disadvantageous for the survival of the males).And certainly not leading to flight. So it shows that the details can lead evolution to flight or to flightlessness-- it's kind of a crapshoot.



BTW, I see that I may have misread some of the intent of the authors referenced in the OP.
I suspect they're talking about the phase space of all possible organisms, and the development of traits to occupy niches not previously occupied is definitely part of expansion in that phase space, even without physical expansion of living space and thus not needing die-offs to make room for expansion.They do imagine a fixed phase space for biodiversity, and then just ask how much of it is filled, and their core result is each sector of that phase space maintains (except for die-offs) a fairly fixed number of families per ecospatial mode. Since expansion is generally exponential, except for the die-offs, they interpret the die-offs as aberrations to the trend. So for them, die-offs are not seen as all that helpful to biodiversity, even in the long run-- but I'm not sure if that is really the last word. A more careful consideration of what would happen without die-offs might be in order.

HenrikOlsen
2010-Aug-27, 05:01 AM
It is only when losing the competition has deleterious effects upon the population's ability to survive that I think it arises to survival of the fittest, otherwise it's survival of the good enough.
Again, it's breeding not survival that matters, and even a 0.00001% higher chance of breeding can compound over many generations to 99.9999% of the population having that trait.
And there have been far more than many generations available.:)

caveman1917
2010-Aug-27, 10:51 PM
Yet Henrik Olsen gave an example of a situation where evolution is stimulated when there is no selective pressure-- because the absence of selection pressure allows a species to adapt "past" a bottleneck. I imagine he had in mind scenarios like, where having feathers on your arms might be nice for cooling you or some such thing, but too many feathers is a downright hindrance that would be selected against in a competitive environment. But in an environment of plenty, with few selection pressures and rapid growth, it might not matter to have those extra feathers-- and then even more feathers might appear, which could be wings.

Yes, i was using the word evolution in the sense of the mechanism that weeds out inferior mutations, not the mechanism by which the mutations are produced.
ETA: basically the same point as Henrik, but he put it much clearer.

whimsyfree
2010-Aug-27, 11:05 PM
You won't limit the population size of competing species if you're the first into a new niche: you'll have no competition right up until you hit the carrying capacity of the niche. I think that's what the authors mean by "expansion and contraction of occupied ecospace, rather than by direct competition": you can only "expand occupied ecospace" by occupying a previously unoccupied niche.


In that case isn't the competition to be the first to occupy new niches? I'm still not sure about the distinction they're making, though I haven't bothered to read the article.

caveman1917
2010-Aug-27, 11:23 PM
In that case isn't the competition to be the first to occupy new niches? I'm still not sure about the distinction they're making, though I haven't bothered to read the article.

As long as the niche is not yet 'filled', the situation is the same as that with unlimited resources. The two are indistinguishable from the perspective of any individual organism involved. And without a limitation on the resources, no competition ensues.

whimsyfree
2010-Aug-27, 11:23 PM
And this is one of my main beefs with the "survival of the fittest" thing, drop the "just".

Evolution isn't about competition between species, it's about competition between individuals of the same species.
When a baby birdie falls out of a nest and is eaten by a cat, evolution isn't happening because the cat survived, it's happening because the sibling which pushed it out, or didn't crawl around, or was better at hanging on in the wind, survived.
Ok, it's also happening because the cat survive, but that's because it is better than its siblings at finding baby birdies to eat.

The competition between species does have a role, but that role is to define the playing field on which the individuals are competing.


I disagree. In your example cats are competing with each other for the baby bird, but they are also competing with (say) lizards that also eat baby birds. From the cat's point of view it makes little difference whether he's beaten to Tweetie Jnr by Sylvester or Scaley.

Ara Pacis
2010-Aug-28, 04:47 AM
If the adaptation rates are vastly different, you would never even know the other species had that capacity, as its evolutionary pressure will be removed before the adaptation can occur. But had the niche remained open indefinitely, they might have eventually entered that niche-- we wouldn't know. Yet that's a race lost.But that argument can become absurd as they need to actually compete to be in competition. We might say that two humans competed for the fastest mile, but if one ran the race 30 years ago and the other yesterday, it's not really a direct competition. More to the point, it might be like saying that a actual quarterback competed with an armchair quarterback: it may be a thought experiment on tactics, but no competition actually occured. Since evolution is directionless, there can be no race to adapt. There can only be competition between existing adaptations, not theorized potential adaptations.


There hasn't been a whole lot of time there-- if we make plastic for a million years, we may find critters adapting to eat it. Microbes probably already are.Yes, some microbes may be. Does that mean there's a race to compete in that niche? Not really. The ability to eat plastic is happenstance.

I agree that competition looks very different in a period of population expansion-- then the winner is the one with the fastest rate of taking advantage of the new ecospace, not the one "most fit" for that ecospace. It's a different type of "fit", and a different type of "competition," but it's all in the spirit of populations controlled by selection pressures of various types.If they are both competing for that ecospace. If one organism evolves an ability to use a new ecospace while another organism does not, the result is not that the one organism won the competition, it's that the organism left the competition. Of course, this can be confused if they are still competing for other resources and the ability to use a new resource makes them better able to compete in the ecospace in which they do still compete.

Ara Pacis
2010-Aug-28, 04:50 AM
Again, it's breeding not survival that matters, and even a 0.00001% higher chance of breeding can compound over many generations to 99.9999% of the population having that trait.
And there have been far more than many generations available.:)

Note that I said survival of the population. That means breeding. If I had said survival of the individual, your critique would be valid.

Ken G
2010-Aug-28, 05:00 AM
But that argument can become absurd as they need to actually compete to be in competition. We might say that two humans competed for the fastest mile, but if one ran the race 30 years ago and the other yesterday, it's not really a direct competition. Yet, if you applied for a job you saw in the paper that you thought you were perfect for, and found that the job had already been offered to someone else before you got there, you'd feel like you'd lost a race there.


If they are both competing for that ecospace. If one organism evolves an ability to use a new ecospace while another organism does not, the result is not that the one organism won the competition, it's that the organism left the competition. Of course, this can be confused if they are still competing for other resources and the ability to use a new resource makes them better able to compete in the ecospace in which they do still compete.The main thing is, evolution is very complex, and although finding simplifying themes is always of value, it can also be misleading.

Gillianren
2010-Aug-28, 06:13 PM
Incidentally, it's my understanding that there are bacteria in a pond in Japan which eat the nylon out of a factory's runoff. I think I read it on Talk Origins somewhere.

caveman1917
2010-Aug-29, 02:22 AM
I agree that competition looks very different in a period of population expansion-- then the winner is the one with the fastest rate of taking advantage of the new ecospace, not the one "most fit" for that ecospace. It's a different type of "fit", and a different type of "competition," but it's all in the spirit of populations controlled by selection pressures of various types.

The view that populations are controlled by selective pressure is a popular one, but one that can lead to many misconceptions. Evolution works on the level of the individual organism. In fact it works on the level of the genes itself - but an individual organism is a good enough proxy, a population however is not.

Consider the perspective of the individual. What he sees is some freely available resources, and some resources that are already claimed by his neighbour. Rather than fight with his neighbour over his resources, he will simply grab the resources that are freely available.
It is not a different type of "fitness" or "competition", there is no competition - and fitness rests undefined. Fitness is nothing more than the measure of how 'good' an individual is relative to some other individual in competition, without 'direct' competition there is no fitness.

It is somewhat akin to for example soccer teams. Fitness in that case would be how good a soccer team is compared to some other. But if they do not compete (do not play eachother), what does fitness even mean?

whimsyfree
2010-Aug-29, 02:32 AM
It is not a different type of "fitness" or "competition", there is no competition - and fitness rests undefined. Fitness is nothing more than the measure of how 'good' an individual is relative to some other individual in competition, without 'direct' competition there is no fitness.

That's not the normal definition of fitness. Fitness is an individual's ability to propagate its genes.

Ara Pacis
2010-Aug-29, 04:39 AM
Yet, if you applied for a job you saw in the paper that you thought you were perfect for, and found that the job had already been offered to someone else before you got there, you'd feel like you'd lost a race there.Not really, not unless we had both been interviewed for it. But even accepting your premise, the analogy fails because I already had the ability to compete for the job, but simply was not in the right place in the right time. As for evolution, There is no right place or right time unless and until the organism mutates into a new organism that has the the new ability. Evolution is like tossing dice, it's not a competition. the competition is in the wagering, but evolution doesn't place bets because evolution has no mind.

The main thing is, evolution is very complex, and although finding simplifying themes is always of value, it can also be misleading.Ah, then you see my point.

Ara Pacis
2010-Aug-29, 04:52 AM
The view that populations are controlled by selective pressure is a popular one, but one that can lead to many misconceptions. Evolution works on the level of the individual organism. In fact it works on the level of the genes itself - but an individual organism is a good enough proxy, a population however is not.

Consider the perspective of the individual. What he sees is some freely available resources, and some resources that are already claimed by his neighbour. Rather than fight with his neighbour over his resources, he will simply grab the resources that are freely available.

I agree. The population competition is a bit of a misnomer, because as soon as an individual mutates and evolves a substantive advantage, it could be said to be part of a new population: the population that has the advantage. In time, the differences may create a new species, and that population may outsurvive the previous population if they still compete for some common resource, or they may live side by side if the evolved advantage is for a different resource for which they do not compete. "Side by side" may be relative, as the advantage-evolved population may relocate to locations where the new resource are more plentiful, if that happens to be the case.

Ken G
2010-Aug-29, 07:50 AM
It is somewhat akin to for example soccer teams. Fitness in that case would be how good a soccer team is compared to some other. But if they do not compete (do not play eachother), what does fitness even mean?But that's a good example of the inverse. Many sports will let the winner of some division get into the playoffs, which often has competed with all of its divisional rivals to achieve that end. But they may also take a "wild card" team with the next best record among all the divisions, even though they may not have played the other wild card teams. So there's no "direct" competition there, yet there still is competition, because if the other team has a better record playing teams your team may not have even played, they could beat you out. That's like winning a niche without directly competing for it, but merely getting there first. Is that competition, or isn't it?

Ken G
2010-Aug-29, 07:56 AM
Evolution is like tossing dice, it's not a competition. the competition is in the wagering, but evolution doesn't place bets because evolution has no mind.It's not just "race" that can be criticized on those grounds-- "competition" and "fitness" are also metaphors that involve anthropomorphization. At some level, we have to use anthropomorphic metaphors-- they are all we can understand. For example, what if we imagine that most species want to go extinct, but their pesky survival instincts get in the way of achieving their goal-- what's "wrong" with that? Let's face it, life can be extremely unpleasant for many living things-- they may be viewed as wanting to get it over as quickly as possible, but they aren't intelligent enough to figure out the concept of suicide, or aren't able to carry it out for various reasons, so instead they fall victim to their instinctive urges to remain alive. Indeed, that view can also be supported by anthropomorphization-- for some unfortunate people, that's just what life can feel like, at least part of the time.

Ah, then you see my point.Yes, the bottom line is, evolution is complex, and any oversimplified metaphor, like "competition", "ecospace", or even "fitness", can sometimes lead you astray. That's what I never liked about the "selfish" gene metaphor, it too is quite anthropomorphizing, but in that case it is unintendedly ironic.

HenrikOlsen
2010-Aug-29, 12:39 PM
Consider the perspective of the individual. What he sees is some freely available resources, and some resources that are already claimed by his neighbour. Rather than fight with his neighbour over his resources, he will simply grab the resources that are freely available.
It is not a different type of "fitness" or "competition", there is no competition - and fitness rests undefined.
There's still the competition to be best at noticing the other resource and at determining to use it.
Competition doesn't have to mean fighting.

Ara Pacis
2010-Aug-29, 04:46 PM
It's not just "race" that can be criticized on those grounds-- "competition" and "fitness" are also metaphors that involve anthropomorphization. At some level, we have to use anthropomorphic metaphors-- they are all we can understand.

True, but I think the way you used it took it beyond the meaning of the analogy. A competition is the comparison of an ability to do something. Evolution isn't an ability. I can't will myself to evolve. Being stuck in the middle of the ocean doen't let me evolve to use gills. For most organisms they can't will themselves out of "water, water everywhere and nary a drop to drink."

caveman1917
2010-Aug-29, 09:58 PM
That's not the normal definition of fitness. Fitness is an individual's ability to propagate its genes.

Indeed, if you will the probability that the genes the individual consists of will appear in the next generation.
And that is my point, in the scenario where resources are unlimited, fitness is not defined in any meaningful way. It is a constant 1 (or 0 if the organism is unviable - but this is obviously always the case), and a parameter that is defined as a constant can hardly be said to be meaningful.


But that's a good example of the inverse. Many sports will let the winner of some division get into the playoffs, which often has competed with all of its divisional rivals to achieve that end. But they may also take a "wild card" team with the next best record among all the divisions, even though they may not have played the other wild card teams. So there's no "direct" competition there, yet there still is competition, because if the other team has a better record playing teams your team may not have even played, they could beat you out. That's like winning a niche without directly competing for it, but merely getting there first. Is that competition, or isn't it?

The scenario i used my example for is one of unlimited resources. By your analogy that would be having at least as many open slots in the playoffs as there are teams. So no team will have to play any other team to get in the playoffs, all of them will have a constant probability of 1 for making it into the next round. Is that competition?


There's still the competition to be best at noticing the other resource and at determining to use it.

Not while the resources can be considered unlimited. It doesn't matter wether you get to your resources faster than your neighbour gets to his, they are disjoint - take as long as you want, nobody could get there before you anyway.

It is only when (local) ecospace gets filled that competition arises again.

HenrikOlsen
2010-Aug-29, 11:42 PM
Not while the resources can be considered unlimited. It doesn't matter wether you get to your resources faster than your neighbour gets to his, they are disjoint - take as long as you want, nobody could get there before you anyway.
You can take so long you die of starvation. :)

Anyway, unlimited resources in the way you suggest is an impossible and thus meaningless ideal; better used for philosophy than biology.

whimsyfree
2010-Aug-30, 12:09 AM
Indeed, if you will the probability that the genes the individual consists of will appear in the next generation.
And that is my point, in the scenario where resources are unlimited, fitness is not defined in any meaningful way. It is a constant 1 (or 0 if the organism is unviable -

No, you've now redefined fitness to suit yourself. If you want to attach a number to it then it is the total number of copies of the individual's genes appearing in future individuals (which hints at the fact that fitness is really about the success of genes, not individuals). More measurable quantities are usually substituted, such as no. of offspring, no. of offspring reaching adulthood, or average relatedness of the next generation to the individual.

Resource constraints are never totally absent and some resources are never unlimited. The fact that you have access to one resource that other species or individuals to not have access to does not mean that you do not face resource limitations. The first plant to fix nitrogen was still competing with other plants for light, water, minerals, etc. In a sexually reproducing species females are a limited reproductive resource for almost all males all the time, so this is an example of a resource which is almost always limited..

transreality
2010-Aug-30, 02:43 AM
Each individual has a subset of genes that are available from a species. So each species has a characteristic genetic diversity. If particular combinations from a species fail, then any genes that are restricted to that subset of combinations may be eliminated, reducing the genetic diversity. Cheetahs are an example of a species pushed by selection to limited genetic diversity. As long as the population of the species is considerable new mutations will not enter the genetic population, so over time in a stable environment a species genetic diversity will slowly reduce. When an extinction event occurs the possibility that a species will not go extinct is probably proportional to its genetic diversity, more than sheer numbers of individuals.

However, as a population nears extinction, the small numbers will allow mutations to enter the genetic code, allowing a new species to evolve with a restored genetic diversity which is dependent on the length of the period during which the population is very small. The possibility that small populations will split from a parent species could well be proportional to the number of available niches in the environment.

Ken G
2010-Aug-30, 04:40 AM
The scenario i used my example for is one of unlimited resources. By your analogy that would be having at least as many open slots in the playoffs as there are teams. So no team will have to play any other team to get in the playoffs, all of them will have a constant probability of 1 for making it into the next round. Is that competition?Unlimited resources is not really relevant-- the "ecospaces" typically support no more than 4 families of taxa at a time, sometimes only 2. The implication is that opening a "new mode" allows for growth in the 2-4 families that "get there first", but all others are severely disadavantaged. That's the kind of "competition" I was referring to. Basically, I just mean that competition is whatever difference you see when there are any other families of tetrapods around, versus when there isn't. And how to factor in predation, I have no idea-- that complicates the meaning of competition a lot, because a prey doesn't compete with its predator, even though it is eaten by it-- predators can do an important job of damping overpopulation and weeding out sick or infirm members.

It is only when (local) ecospace gets filled that competition arises again.Right, but that is part of the competition we have in mind-- whether or not someone else has already filled the ecospace. I don't disagree with the authors that competition within a saturated ecospace probably is not the path to biodiversity, I'm just pointing out instead that competition in a filled ecospace would seem to play a key role in limiting biodiversity. So expansion or contraction of ecospace must be part of a story that also includes competition if you want to understand the biodiversity you get.

caveman1917
2010-Aug-30, 09:00 PM
No, you've now redefined fitness to suit yourself.

I was using the Hartl definition, "the probability that an individual will be included in the selected group of parents for the next generation".
I had been told it is an accepted measure of fitness in biology, though admittedly i could only say for sure about its use in evolutionary computational models.


Resource constraints are never totally absent and some resources are never unlimited. The fact that you have access to one resource that other species or individuals to not have access to does not mean that you do not face resource limitations. The first plant to fix nitrogen was still competing with other plants for light, water, minerals, etc.

That is true, but it appeared to me that a temporary flattening of the fitness landscape would account for the ability of "hopping" from one local maximum to another.
How would you account for that?


In a sexually reproducing species females are a limited reproductive resource for almost all males all the time, so this is an example of a resource which is almost always limited..

Fair enough :)

caveman1917
2010-Aug-30, 09:16 PM
Unlimited resources is not really relevant-- the "ecospaces" typically support no more than 4 families of taxa at a time, sometimes only 2. {...} So expansion or contraction of ecospace must be part of a story that also includes competition if you want to understand the biodiversity you get.

Perhaps we have been talking past eachother. I was only trying to see what model would account for the effects where the inferior mutations are not selected against during those periods. To me it seemed that a flattening of the fitness landscape, allowing the population to perform a random walk instead of hill-climbing could account for this.
Thus it seemed that (for that specific window of time) the situation could be likened to one with unlimited resources.

Ken G
2010-Aug-31, 02:02 AM
Perhaps we have been talking past eachother. I was only trying to see what model would account for the effects where the inferior mutations are not selected against during those periods. To me it seemed that a flattening of the fitness landscape, allowing the population to perform a random walk instead of hill-climbing could account for this.
Thus it seemed that (for that specific window of time) the situation could be likened to one with unlimited resources.I'm not sure we're really disagreeing, I'm just saying that there is no such thing as not being selected against-- there's always some kind of selection going on. There's competition for mates, there's selection by predators and disease, and above all, there's selection around access to the new resources (a bird that flies better will be in a better position to take advantage of airspace). I think the issue all centers on the meaning of "competition", which is generally interpreted pretty broadly in the "survival of the fittest" viewpoint, but which the authors of the OP article seem to be interpreting very narrowly (i.e., they are only talking about a form of competition that increases biodiversity within a saturated ecospace, which is kind of an odd thing for competition to do in the first place-- it would seem to limit biodiversity within a saturated ecospace).