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Author Topic:   Human Evolution
Quetzal
Member (Idle past 4290 days)
Posts: 3228
Joined: 01-09-2002


Message 27 of 36 (448799)
01-15-2008 9:43 AM
Reply to: Message 17 by Elmer
12-25-2007 10:51 AM


Natural Selection and Biodiversity - An Example
Since the OP is ludicrous on its face, I think a topic divergence is in order.

Hi Elmer (if you're still around). I think you might be missing some element of either "natural selection" or "biodiversity". You say:

That means that, unlike scientific causal forces like gravity and the electromagnetic force and the nuclear forces, "Natural Selection" is not a universal causal mechanism, even though it is constantly put forward as if it were such. NS being in truth, no more than a label for any strictly local, relative, anomalous and particular mortality event, biodiversity is neither generated nor prevented by it. (emphasis added)

I work with biodiversity, at least conceptually, on a nearly daily basis. Even as we speak, I'm in the throes of designing study protocols for a biodiversity conservation project that simply would not work if NS didn't influence biodiversity (IOW, I'm goofing off on EvCForum instead of working). Apologies for the length of this response, but I think it pretty illustrative of how NS influences and changes biodiversity.

One of the critical problems facing conservation biologists and ecologists trying to develop effective techniques for monitoring biodiversity is the simple physical fact that you can’t – with the best will in the world – observe and count every single individual of every species that might be of importance or interest. In other words, we have to come up with ways of monitoring and measuring the ecological integrity of a particular area that don’t rely on direct observation. This isn’t as easy as it sounds. There has been a tremendous amount of ink spilled over the issue. What we have to find are critters or guilds (a number of different species that taken together occupy a particular niche or fulfill a specific ecological function – for instance, the guild of fruit eating birds, etc) that can serve as “stand-ins” for the overall biodiversity of a site.

In my case, I have chosen to focus on the dung beetle guild (subfamily Scarabaeinae) as a viable stand-in for ecological integrity and ecosystem health (not real sexy, I know, but hey – whatever works). These beetles play an absolutely crucial role in decomposition and nutrient recycling. If they didn’t exist, we’d have to invent them or be hip-deep in rotting poop. A number of species in this guild have adapted to the loss of large mammals (during the Pleistocene extinction) and hence the loss of large-mammal-poop by developing obligate saprophagous (rotting fruit) or necrophagous (rotting cadaver) behavior. What makes these critters so useful for conservation is that in the same geographic areas, the taxonomic composition of the guild within forests is completely distinct from that in areas where the forest has been cut or otherwise disturbed. The internal structure and organization is also different. It’s possible to differentiate between guilds found in disturbed habitat, undisturbed habitat, and transitional habitat.

Here’s where natural selection and biodiversity intersect: changes in organization, structure and composition over time serve as valid and accurate indicators of change within each type of habitat. The guild clearly reflects anthropogenic (human-caused) change: defaunation, fragmentation, ecosystem simplification, introduction of exotic and/or domestic animals (e.g., cattle), etc. Not only will it reflect negative changes in the habitat, but we can use it to track positive changes due to management intervention (including re-forestation, landscape restoration, the effects of the reintroduction of locally extinct species, etc).

Now why is this? Because selection pressures (i.e., natural selection) are subtly different in each type of habitat. Natural selection either eliminates or promotes whole populations of different species of this guild, thus reflecting changes in selection pressures and causing changes in guild composition, diversity and population density. And we can watch the change occurring right before our eyes.

If NS had nothing to do with biodiversity as you state, how could I use the Scarabaeinae to monitor ecosystem integrity?

If you want to discuss this any further, we need to take it to a new thread.


This message is a reply to:
 Message 17 by Elmer, posted 12-25-2007 10:51 AM Elmer has responded

Replies to this message:
 Message 31 by Elmer, posted 01-15-2008 8:30 PM Quetzal has responded

Quetzal
Member (Idle past 4290 days)
Posts: 3228
Joined: 01-09-2002


Message 32 of 36 (449075)
01-16-2008 1:11 PM
Reply to: Message 31 by Elmer
01-15-2008 8:30 PM


Re: Natural Selection and Biodiversity - An Example
Too bad. I'm a great friend of empiricism in science, myself. Computer simulations lead to too many suppositions passed off as facts, IMHO.

Who said anything about computer simulations? An indicator species (or guild, in this case) is intended to be representative of the integrity of a particular area, ecosystem, habitat, community or what-have-you. They are surrogates for other (less easily monitored) species and the ecological processes that support them. Meaning that a statistically significant change in the biological pattern of the indicator is a signal that something is going on with the biota as a whole, and by extension the ecological integrity of the landscape. I imagine you could make a computer model, but the only “supposition” involved here is that the responses of the indicator to stress reflect the response of all the rest of the species assemblages and ecological processes of interest. It seems to work pretty well, and is pretty straight forward empiricism.

Like I always say, adaptation and evolution are wonderful things. They just don't have anything to to with "Natural Selection"--unless you've found a novel definition for "NS" that I have yet to hear. Have you?

It sounds like you’re the one with some odd-ball definition of natural selection. If the composition of the guild (species diversity, species distribution, functional distribution, relative population density, etc) is NOT dependent on natural selection, what is it dependent on? These organisms aren’t adapting – the various species groups in this guild, and the resultant composition etc, we see on the ground, is utterly different from one habitat type to another due to very subtle differences in selection pressures from one microsite to another. In fact, there’s a continuous gradient in species composition and structure between different habitats that directly mirrors the ecological gradient between habitats. This guild is SO sensitive that with careful sampling, you can actually watch changes in habitat over time, by monitoring changes in the guild. Natural selection is the only mechanism that explains this. If you have some other explanation, my colleagues and I would absolutely love to hear it, since effective biodiversity monitoring is one of our biggest headaches.

Sounds redundant [or tautologous] to me--'change in ecology equals change in ecosystem'. If you are trying to say that change in biodiversity in an ecosystem correlates to changes in that ecosystem, that's true, and that correlation/correspondence is adaptation-dependent.

Change in the ecology of whatever level we care to talk about is most assuredly not “adaptation-dependent” (whatever that means). Biodiversity is dependent on the characteristics (biotic and abiotic) of the site in question – whether you’re talking at the level of a stream riffle or an ecoregion. Changes in biodiversity – no matter if we are discussing species assemblages in the entire Amazon or the extinction risk of an endangered population in a tiny habitat fragment - are directly correlated to changes in these characteristics. In other words, to changes in selection pressures (i.e., natural selection). If it wasn’t, then monitoring Scarabaeinae guild composition would be an utterly futile waste of effort. Again, if you have another mechanism to propose, I want to hear it. I’d hate to waste my time slogging through a forest with buckets of rotting fruit if I didn’t have to. If the changes I observe in my beetles AREN’T correlated with changes in selection pressures, then this whole effort is moot, wouldn’t you say?

Well, no, that's just talk. The only fact is that different organisms are suited [fitted, adapted] to different environments. Change their environment and you change their level of adaptedness, and hence, their mortality rate. A simple truism, as above. No need for fanciful literary allusions to some allegorical 'selecting agency'. Adaptedness is a fact of life, and adaptedness, or the lack of it, is not 'natural selection'.

Precisely – different organisms are more suited to particular environments. Change the environment – to include all the factors that make up that term - and different organisms do better in the new conditions than their predecessors (biogeographically not ancestrally speaking). The mechanism of that turnover in species assemblages is natural selection. The varied selection pressures imposed by the environment are what causes the changes in biodiversity – again at whatever level you want to examine. “Adaptation” has little or nothing to do with biodiversity. What and how many (i.e., “biodiversity”), IS, however, completely dependent on the environmental conditions present at whatever scale you’re observing. “Environmental conditions” is synonymous with the factors (“selection pressures”) that make up natural selection.

Since all you seem to be doing is biometrics [and I'm not being disrespectful--biometrics is very useful to ecology, and ecology is desperately important to us all, these days!], and biometrics is just measuring effects that have quite obvious physical causes [eg., guns and bulldozers], or unknown biological causes [evolution], I suggest that you could do your job without ever once having to invoke a mystical agency called, 'natural selection'.

I think you’re using the term “biometrics” incorrectly. I’m not actually weighing and measuring the beetles, just tracking guild composition (aka biodiversity).

You might “suggest” I don’t have to invoke natural selection, but you just did: guns, bulldozers, deforestation, defaunation, etc, are all selection pressures and the action of all these pressures on the population, species, guild, whatever, taken in toto, is what is referred to as natural selection.

Watching change is not explaining change. Attributing the cause of organismic, [or even ecosystemic], change, to a literary analogy, a trope, a figure of speech, is not explaining anything.

Perhaps. However, in the absence of any other explanation, understanding causes of the observed change by seeking to understand the response of the population to changes in environmental factors (e.g., selection pressures), remains the best way to bet. In other words, until someone comes up with a better explanation for what is actually observed, I'll go with the one that works: natural selection.


This message is a reply to:
 Message 31 by Elmer, posted 01-15-2008 8:30 PM Elmer has responded

Replies to this message:
 Message 33 by Elmer, posted 01-16-2008 5:07 PM Quetzal has responded

Quetzal
Member (Idle past 4290 days)
Posts: 3228
Joined: 01-09-2002


Message 34 of 36 (449133)
01-16-2008 7:12 PM
Reply to: Message 33 by Elmer
01-16-2008 5:07 PM


Re: Natural Selection and Biodiversity - An Example
I hate it when that happens. Anyway, don't worry about it. We should probably take the discussion to a more appropriate thread.(I hear the topic police running up behind us with heavy clubs). Would Razd's diversity thread work? I need to read it (I was off-line mostly when it was going on, but it looks promising.

This message is a reply to:
 Message 33 by Elmer, posted 01-16-2008 5:07 PM Elmer has not yet responded

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