Why are there so many species of beetles and so few crocodiles?

Aug 28, 2012
The relationships between age and species richness in major groups reveals that in almost every major group, age and diversity are not strongly correlated, life scientists report. Credit: Amisha Gadani

There are more than 400,000 species of beetles and only two species of the tuatara, a reptile cousin of snakes and lizards that lives in New Zealand. Crocodiles and alligators, while nearly 250 million years old, have diversified into only 23 species. Why evolution has produced "winners"—including mammals and many species of birds and fish—and "losers" is a major question in evolutionary biology.

Scientists have often posited that because some animal and plant lineages are much older than others, they have had more time to produce new species (the dearth of crocodiles notwithstanding). This idea—that time is an important predictor of species number—underlies many used by biologists. However, it fails to explain across all multi- on the planet, a team of life scientists reports Aug. 28 in the online journal , a publication of the .

"We found no evidence of that," said Michael Alfaro, a UCLA associate professor of ecology and and senior author of the new study. "When we look across the tree of life, the age of the group tells us almost nothing about how many species we would expect to find. In most groups, it tells us nothing."

Another idea, that some groups are innately better or worse at producing species, similarly fails to explain differences in species number among all of the major living lineages of , the found.

"We know that some groups, like or , have been exceptionally good at producing species during certain periods of their evolutionary history," Alfaro said. "However, when we look at the ages of all of the major groups of plants and animals, these differences in speciation rate are not sufficient to explain the differences in species number that exist in extant groups."

Alfaro and his colleagues studied 1,397 major groups of multi-cellular eukaryotes—including animals, plants and fungi—that account for 1.2 million species. Working as "evolutionary detectives," they were able to see whether the groups that split the earliest tended to have the most species. They assigned a "species richness score" to these 1,397 groups, using novel statistical and computational methods they developed.

If age does not explain species diversity, an alternative idea is that a lineage will produce species up until the point that it fills an "adaptive zone" that allows a maximum number of species, Alfaro said. In other words, a lineage of bats, whales or penguins has a maximum capacity that is determined by habitat requirements and competitors.

When an adaptive zone is first colonized, the growth of new species will be rapid, up until that limit has been reached. Once a zone is full, this speciation rate will level off. New species will not emerge until one of two events occurs: First, an existing species may go extinct, in which case it may be replaced. Second, a species within the adaptive zone may evolve a new trait—sharp teeth, wings, chemical defenses or camouflage, for example—that confers a significant ecological advantage and takes it into a new adaptive zone, creating opportunities for new species to emerge, Alfaro said.

"Adaptive zones are an old idea in evolutionary biology, but there is little understanding of whether speciation rates or adaptive zones are more important in explaining species richness across the tree of life," Alfaro said. "If adaptive zones control biodiversity at the broadest scales, then the rate of species growth will be a good explanation of species richness only right after a lineage has entered into a new adaptive zone. Once the adaptive zone has filled up, then, no matter how much time goes by, the number of species will not change much."

Thus, these adaptive zones, which Alfaro also calls "ecological limits," serve to restrict the number of new species that can emerge.

"Most of the groups that we studied have hit their limits," he said. "Ecological limits can explain the data we see. What's really driving things is how many times lineages evolve new innovations that move them into new adaptive zones.

"The ultimate goal in our field is to have a reconstruction of the entire evolutionary history of all species on the planet," Alfaro added. "Here we provide a piece of the puzzle. Our study sheds light on the causal factors of biodiversity across the tree of life."

Explore further: Bee-flies and false widow spiders top Museum enquiry

More information: In a 2009 study published in Proceedings of the National Academy of Sciences, Alfaro and his colleagues reported that mammals and many species of birds and fish are among evolution's "winners," while crocodiles, alligators and a reptile cousin of snakes and lizards known as the tuatara are among the "losers." That study also showed that new species emerge nearly as often as they die off.

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TheGhostofOtto1923
2.7 / 5 (29) Aug 28, 2012
Beetles have many many more potential niches they can occupy.

Next question.
ValeriaT
1 / 5 (3) Aug 28, 2012
Why are there so many species of beetles and so few crocodiles?
IMO the answer of this question is in predator-prey adaptation: the predators tend to specialize to dedicated prey, which evades them with changing of its appearance (morphology) and it avoids this particular predator, which forces the predator to change its morphology and to adapt again, and so on in neverending cycle leading to extensive speciation and biodiversity. With compare to insect predators the crocodiles are occupying the end of food chain and they're not specialized to any particular prey.
Argiod
1 / 5 (4) Aug 28, 2012
...a purely emotional response:
Have you ever heard the saying; up to your butt in alligators (or crocks, in this case)? If there were as many crocks or gators as insects, there would hardly be room for anything else...
ValeriaT
1 / 5 (3) Aug 28, 2012
You're right, large organism cannot be diversified very much, because the number of their individuals cannot be too high. But the very small organisms cannot be very diversified too, because their genomes are tiny accordingly - for example the bacteria tend to form clones rather than individual species. Now I can recall my theory, in which the maximal complexity of the observable Universe falls into distance scale 0,2 - 2 cm, which corresponds the wavelength of CMBR radiation and which represents the area of competition of intrinsic and extrinsic perspectives of observable reality - the relativity and quantum mechanics. Most of different forces and interactions falls into this distance scale too (Cassimir force, dipole and VanderWaals forces, surface tension and capillary forces, etc). If the life was supposed to evolve from physical systems spontaneously, it was excepted to do so just at the distance scale, at which the complexity of physical world was highest already.
SatanLover
1 / 5 (2) Aug 29, 2012
first of all because beetles are smaller and have shorter life span they have a lot of stress factors in their environment.
as for crocodiles they are big have bigger lifespan and or on top of a food chain, they are well built so they have less stress factors.

my answer on the title, article TL;DR
antialias_physorg
not rated yet Aug 29, 2012
It might be worth it to test niche size, niche number and niche stability as indicators for number of species

If a niche is large more species can coexist without direct competition that will drive one to extinction.
If there are many possible niches for a species then it can speciate more readily into subgroups that do not compete to extinction
If a niche is stable the time for speciation is increased (although an unstable niche is more likely to force faster mutation)

But the very small organisms cannot be very diversified too, because their genomes are tiny accordingly

The upper genome size between insects and mammals is not markedly different
http://en.wikiped...izes.png
TheGhostofOtto1923
2.8 / 5 (24) Aug 29, 2012
If a niche is large more species can coexist without direct competition that will drive one to extinction.
Regardless of size, only one species can inhabit any particular niche.

"a niche is a term describing the way of life of a species. Each species is thought to have a separate, unique niche."

"Different species cannot occupy the same niche (or guild). A niche is a very specific segment of ecospace occupied by a single species."
http://en.wikiped...al_niche

"Over time, two competing species can either coexist, through niche differentiation or other means, or compete until one species becomes locally extinct."
http://en.wikiped...ntiation

-Perhaps you are thinking of habitat. A habitat can include many potential niches for different species to occupy. The more diverse the habitat, the more species can occupy it.
Torbjorn_Larsson_OM
1 / 5 (1) Aug 29, 2012
"But the very small organisms cannot be very diversified too, because their genomes are tiny accordingly".

The largest genome size span is among the smallest eukaryotes, the largest extant genome may (controversial) be an amoeba, the unicellular Trichomoniasis (commonly causing vaginitis) genome is 3 times the size of the human genome. [ http://en.wikiped...me_sizes ]
antialias_physorg
3 / 5 (2) Aug 30, 2012
Regardless of size, only one species can inhabit any particular niche.

A niche is not a well defined concept. For example the Earth is a niche - and it sustains many species that don't cause each other to go extinct.

You can have a niche where one organism is better adapted to it than another but yoo still may get a system where they don't outcompete each other (e.g. if both have certain breeding grounds and don't venture far enough to come into contact with the other). Such a niche could be indefinitely stable for both even without any possible way to delineate the environment (by blocking mountains, oceans or whatever)

Then there are niches with an overabundance of resources but where the species themselves have some self limiting factor which prevents growth beyond a certain maximum number (as in the above example). In such a niche even maladapted species can coexist.
Vendicar_Decarian
1 / 5 (1) Aug 30, 2012
Organisms with shorter life cycles have more opportunity for speciation over any given interval.

Done.
TheGhostofOtto1923
2.7 / 5 (24) Aug 31, 2012
A niche is not a well defined concept. For example the Earth is a niche - and it sustains many species that don't cause each other to go extinct.
Sorry you didnt read the link which indicates that you would rather make stuff up than look stuff up.

The earth is not a niche in any sense of the word.
. if both have certain breeding grounds and don't venture far enough to come into contact with the other).
Uh this would be 2 different niches? Research first, then post.
TheGhostofOtto1923
2.6 / 5 (27) Aug 31, 2012
This niche business makes me wonder if it is not indicative of why unregulated free market capitalism, indeed capitalism at all, is a myth? No 2 competitors can occupy any one niche for long without one winning out. This must be the same in business. As the niche fills up, competition intensifies and one species will extinct the other by whatever means is at their disposal; or force them to adapt to a new niche.

More than one company can never occupy the same niche for long without extraordinary and overarching Control. Competition benefits society but it is obviously not self-sustaining.

Or we can assume that 2 companies which are doing so in an apparently stable relationship, are actually Iterations of the same Entity which is Operating above a Level we are aware of.

This is also true with political and religious constructs. I am sure some economist has written this up already, but not including the overarching Component. Or else he wouldnt get published or invited on MSNBC.
Estevan57
2 / 5 (29) Aug 31, 2012
Otto, with your overiding personality disorder it is not hard to imagine you dismissing the idea of coexistance. Spiro Agnew.
antialias_physorg
3 / 5 (2) Aug 31, 2012
Uh this would be 2 different niches? Research first, then post

Take the example of the ocean: In every milliliter of seawater are many different species of phytoplankton - but they all occupy the same niche: feeding on sunlight. Some do it better than others. All survive. No one species outbreeds another into extinction.
C_elegans
5 / 5 (1) Sep 01, 2012
Beetles have many many more potential niches they can occupy.

Next question.


You mean that many species of beetles can occupy many niches, right?

Also, a mL of seawater is not a niche. Niches are not volumes, they are ecologies. They may include migration across large distances during the lifespan of that organism.
antialias_physorg
5 / 5 (1) Sep 01, 2012
Also, a mL of seawater is not a niche.

The point was that different types of phytoplankton does occupy the same niche (spatially, food source and all other matters) and they don't cause each other to go extinct.
TheGhostofOtto1923
3 / 5 (22) Sep 01, 2012
Also, a mL of seawater is not a niche.

The point was that different types of phytoplankton does occupy the same niche (spatially, food source and all other matters) and they don't cause each other to go extinct.
The term 'niche' necessarily includes the species which occupies it. Therefore your different types of phytoplankton occupy different niches.

"a niche is a term describing the way of life of a species. Each species is thought to have a separate, unique niche."

-You should be a little more specific. Are these different species consuming the exact same nutrients? Are consuming them at different times? Is their existence complimentary or symbiotic? Do they spawn at different times and different places?

I could do the research but I think you need the practice.
TheGhostofOtto1923
2.8 / 5 (22) Sep 01, 2012
Aw I couldn't resist. Hints of differentiation:

"Thus two kinds of species are described: adapted-to-impoverished-nutrient, broader niched species; adapted-to-improved-nutrient, narrower niched species"

More hints:

"The biogeochemical role of phytoplanktonic organisms strongly varies from one plankton type to another... In situ observations find dominant types often associated to specific physical and chemical water properties."

Und:

"Ecological Niches[pl] of Sympatric phytoplankton Species[pl]" m levandowsky

-und so weiter. I think your knowledge base may need updating.

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