A thought..

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BashHarris
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A thought..

Post by BashHarris » October 23rd, 2012, 7:19 am

In my ecology class we're learning about interspecific competition, leading one species to evolve to fill another niche. I couldn't help but think of the Queen snake, who primarily feeds on freshly molted crayfish, which lives among water snakes that eat damn near everything. I wonder if Nerodia pushed Regina to it's oh so specific diet? Lol thought I'd share with some fellow nerds..

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Nick Scobel
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Re: A thought..

Post by Nick Scobel » October 23rd, 2012, 2:49 pm

It's a possibility. But there's many factors besides interspecific competition that would cause Regina to occupy such a narrow niche. If anything, I think this species was able to occupy an evolutionary niche which was so narrow that it allowed for this species to be as successful as it is because the niche allowed for little/no competition for resources. But that's just my $0.02 on the issue. I'd be interested to hear other opinions, great question!

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ugh
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Re: A thought..

Post by ugh » October 24th, 2012, 4:36 am

Nick I don't think anyone doubts it's specialized diet allowed it to continue its success through today; his question re: how Regina arrived at such a narrow niche in the first place. But I'd like to hear what you think these other factors are; I'm still thinking on that one lol.

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BashHarris
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Re: A thought..

Post by BashHarris » October 24th, 2012, 7:01 am

That's an interesting way to look at it Nick. With the immense population of Water snakes, I kind of think it may have bullied the other aquatic serpents to fill or even create new niches. If you think about any of the other snakes who chill around the water up in the North, they seem to have contrasting diets to that of the water snake. Such as the rough greens and whatnot.

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Re: A thought..

Post by Matt Buckingham » October 24th, 2012, 10:23 am

Let's clarify your question a bit:

Are you asking if R. semptemvittata could have once been generalists but due to competition from Nerodia made a facultative switch to specializing on crayfish?

If that's your question I would say no. If this were the case we would have to assume a number of things: (1), that this species was once a generalist - which I find unlikely due to its rather narrow habitat preference, unless you also assume that it once occurred in a much broader array of habitats. (2) that it was present in these habitats at the time or before the arrival of Nerodia. I don't know enough about the evolutionary history of snakes to comment on this either way, but I think that is probably unlikely. (3) that there was a genetic basis for the shift in foraging ecology that occurred in high enough concentrations in the population to allow enough individuals to successfully switch foraging preferences without dropping the population below a critical level.

What I think you are asking is whether or not competition between Nerodia, and/or other genera led to the speciation of semptemvittata from an ancestral Regina or other ancestral genus. It certainly would have had an impact. Evolutionarily speaking the more general a species can be in preference, the more successful it will be. So as a species evolves, it will evolve to take advantage of all available resources. Imagine it like a crude chart tracking the evolution of all species over time: Super General - Sort of General - Barely General - Specialist. You won't likely see any super generalists evolve in current geologic time unless there is some die-off event that opens up a vast array of resources. That's not to say it's impossible though - occasionally something evolves a better way to take advantage of general resources (look at human beings!)

So I would say that competition was/is a major driving force in the speciation of semptemvittata and any other habitat/food resource specialist species. Like Nick said, there was probably a resource available that had not been previously exploited by another species. In this case competition would still be the reason that it was driven to that niche.

Though Queen snakes require a specialized habitat and food resource, both occur in abundance on the landscape, so they are currently not a factor that would limit the population size. So saying that the Queen snake is successful is a bit misleading. It is successful at occupying a rather wide ranging niche, but Evolutionarily speaking it's not particularly successful, in that if this particular niche was lost or altered to a degree that could no longer sustain populations, it would either vanish or radiate, depending on the time frame.

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Re: A thought..

Post by Matt Buckingham » October 24th, 2012, 1:30 pm

I'd like to clarify something else regarding this comment:
I kind of think it may have bullied the other aquatic serpents to fill or even create new niches.
Organisms in nature are incapable of creating ecological niches. While there are varying concepts as to what specifically a niche is, it generally boils down to a collection of environmental and ecological factors that lead to the potential for occupancy by an organism, species, or other taxonomic group combined with the manner in which said group or species occupies and utilizes these resources and conditions. And niches occur on multiple scales. For example you can say that all life has a niche, and list the specific conditions necessary for life, down to the niche of one population of a given species. Though generally speaking in ecological literature niche applies to the specific conditions occupied by a species.

What all this means is that the conditions necessary for a niche to be filled has to exist already in nature in order to be occupied. What can happen through evolutionary processes, is the manner in which a species utilizes a resource can change. In this case a new niche has been created through various processes, but the organism itself has not created it.

Sounds like a cool class. What degree are you pursuing?

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Re: A thought..

Post by Nick Scobel » October 24th, 2012, 10:43 pm

ugh wrote:Nick I don't think anyone doubts it's specialized diet allowed it to continue its success through today; his question re: how Regina arrived at such a narrow niche in the first place. But I'd like to hear what you think these other factors are; I'm still thinking on that one lol.
I wasn't trying to make a specific point about the factors. I was just simply trying to state that queens weren't just bullied into a particular niche due to "bullying" by Nerodia.

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Re: A thought..

Post by Matt Buckingham » October 25th, 2012, 8:40 am

Nick Scobel wrote:queens weren't just bullied into a particular niche due to "bullying" by Nerodia.
Exactly. I didn't address this point in my previous comments. OP: I'm not sure how you meant it, but bullying to me implies some act of aggression. I seriously doubt that aggression had anything to do with pushing Queen snakes into their niche. Nerodia, and/or whatever other competing genus or genera were around during their speciation were likely simply better at exploiting a broader resource. Remember a major driving factor in evolution is that more individuals are produced than can be sustained by the resource.

We can rule out aggression because Queen snakes are still sympatric with some Nerodia species.

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Re: A thought..

Post by Nick Scobel » October 25th, 2012, 8:22 pm

Matt Buckingham wrote:
Nick Scobel wrote:queens weren't just bullied into a particular niche due to "bullying" by Nerodia.
Exactly. I didn't address this point in my previous comments. OP: I'm not sure how you meant it, but bullying to me implies some act of aggression. I seriously doubt that aggression had anything to do with pushing Queen snakes into their niche. Nerodia, and/or whatever other competing genus or genera were around during their speciation were likely simply better at exploiting a broader resource. Remember a major driving factor in evolution is that more individuals are produced than can be sustained by the resource.

We can rule out aggression because Queen snakes are still sympatric with some Nerodia species.
Matt, I think "bullying" was his way of trying to convey that Nerodia and other genera to were better able to exploit a broader resource, rather than aggression.

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Re: A thought..

Post by Matt Buckingham » October 26th, 2012, 5:46 am

ugh wrote:\But I'd like to hear what you think these other factors are; I'm still thinking on that one lol.
Well there are a suite of factors that drive speciation.

We've already addressed interspecific competition, but intraspecific competition is also a major driving factor, perhaps even moreso. Remember that one of the conditions that has to be met for natural selection to occur is that there are more offspring produced than can be supported by the environment. So with resources being limited, Queen snakes and their congenerics may have split from a common ancestor to be able to partition the resource or be able to take advantage of new resources.

Geographic or physiographic isolation is another possibility. To make any guesses about the specifics that may have caused this we would have to know when approximately the radiation of modern Regina occurred, which I don't, but if some barrier is created that separated the common ancestor of Queen snakes and other congenerics to a degree that gene flow was no longer possible, then species would begin to diverge.

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BashHarris
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Re: A thought..

Post by BashHarris » October 29th, 2012, 8:07 am

I appreciate everyone's feedback. I understand all that you're implying. I think my choice of words may have been taken too literal however. "Bullying" in my context simply meant one species out-doing the other for resources. Not an act of aggression. I understand a number of ecological factors contribute to the formation of a niche. All I was saying is I believe Regina's selective diet may have at least partially been a result of a prominent, Nerodia who inhabits the same territory and who's diet is so vast. As well as possibly a Thamnophis, bird of prey, and other interspecific relationships. I'm simply hypothesizing that Nerodia may have been one, along with other ecological pressures.

Just thought I'd clarify my claim. Thanks for your feedback guys.

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