Scientists challenge current theories about natural habitats and species diversity

December 27, 2012, Hebrew University of Jerusalem
Preserving biodiversity: A typical tropical rainforest scene in Daintree National Park, Queensland, Australia. Credit: WikiMedia Commons

(—How can a square meter of meadow contain tens of species of plants? And what factors determine the number of species that live in an ecosystem? Science journal has defined this as one of the 25 most important unresolved questions in science, both for its importance in understanding nature and due to the value of natural ecosystems for mankind. The value of goods and services provided by natural ecosystems is estimated to exceed the GDP of our planet.

For over 50 years, conventional ecological theories have predicted that the number of species that can coexist in a given area increases with the heterogeneity of the environmental conditions in the habitat. This premise was examined in a study conducted by research students Omri Allouche and Michael Kalyuzhny, guided by Prof. Ronen Kadmon from the Alexander Silberman Institute of Life Sciences at the Hebrew University of Jerusalem, in collaboration with Prof. Gregorio Moreno-Rueda and Prof. Manuel Pizarro from Universidad de Granada.

The researchers claim that in a heterogeneous environment—where there are many different types of habitats—there are fewer resources and less suitable area available to each species, making them more vulnerable to local extinction. This leads to the hypothesis that excessive habitat heterogeneity may actually reduce the number of species.

This hypothesis was examined using mathematical models and of . Its predictions were examined with a meta-analysis of tens of datasets of plant and animal species from various localities worldwide.

Both the theoretical results and the data analyses supported the researchers' hypothesis that habitat heterogeneity may increase the rate of and therefore reduce the number of species that inhabit the ecosystem.

These findings are very important for the conservation of biodiversity, since the current practice is to conserve areas of maximal habitat heterogeneity and even to take measures to increase habitat . The study shows that this conventional approach may lead to negative results, especially in the case of landscapes of limited size, which is typical of nature reserves.

Ecosystems and the they consist of are under increasing pressure of human activity. In these conditions, skillful and intelligent management of natural landscapes is vital. This study provides scientists and policy makers with important insights for the selection and management of areas for conservation.

The study, Area–heterogeneity tradeoff and the diversity of ecological communities, was published in the Proceedings of the National Academy of Science. It was funded by the Israel Science Foundation and by Israel's Ministry of Science and Technology.

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2.5 / 5 (2) Dec 27, 2012
Habitat heterogeneity at one instant is not the same as habitat heterogeneity over a longer time period.
3 / 5 (2) Dec 27, 2012

You are certainly right. However, if environmental conditions are fluctuating, it will only further destabilize the local populations and make them more extinction prone. And so the number of species at sites with higher AVERAGE heterogeneity will decrease even further.
not rated yet Dec 27, 2012
Food forest gardening and permaculture. Start there. You'll understand everything you need to know about sustaining biodiversity and polyculture systems. A great place to start would be
1 / 5 (1) Dec 30, 2012
One word: fractals. The fractal nature of nature itself has not been anywhere nearly adequately studied by our species, because in modern society - say, the past 50 to 500 years (hey! a somewhat fractal time scale...) - we have chosen unwisely to surround ourselves with every system linear, and squared-off, and man-made, and un-natural and un-fractal (yes, I know that that is not a word). We're drowning in systems of a low fractal dimension, so nature seems foreign to us, being that nature is of a high fractal dimension. Nature doesn't have perfect 90-degree tree branches or perfect 60-cycle lake surface shimmers, or things like that. This series of decisions down a non-fractal lifestyle that our society is precariously perched on top of, leads directly to our loss of imaginative thought, so here we are asking questions that should've been answered long ago, like the questions posed at the beginning of this article. Study fractals, irrational systems, analog in dominance of digital,etc
not rated yet Dec 30, 2012
One word: fractals.

One word: wrong

There are things that look fractal in nature but not to many levels (3 or 4 at most - then you run into other things like irreducible sizes of cells towards the small and structural/nutritional/resource problems on the larger end)

Fractals are a nice buzzword for the 'esoteric crowd' and they have a number of uses (I actually used them in a small part of my thesis for the characterisation of artrhitic processes because the bone structure is fractal to a very limited degree)

But by and large they aren't particularly useful in describing biology accross a wide range of scales (which is what fractals are meant to do).

Fractals have an unspoken assumption which is that forces that shapes them are scale invariant. But forces in nature aren't size invariant. At small scales other forces dominate/are relevant to a cell, an animal (or a species) than at larger scales.
not rated yet Jan 01, 2013
Intriguing, since I assume it means there is some sort of balance where habitat heterogeneity is balanced in terms of number of species and their clustering.
not rated yet Jan 01, 2013
"Fractals". Indeed wrong. Just throwing an ad hoc term out there is pseudoscience, and that is in this case tested by having the generic pattern search plea inserted.

As a matter of fact we know that many systems are *not* fractals, since they would follow power laws. But people do a similar sloppy job of not testing for power laws when they just make such fits instead of statistical tests. Unfortunately in this case it is 'within the biz', math fools many and you yourself is the easiest person to fool, and many such papers are published through peer review even.

Statistician Cosma Shalizi et al tested predicted power laws made from fits, and they were about as often generic exponentials distributions of classically dimensionalized dynamic processes. (Googleable from this info.)

Yes, in many cases it may be a fractal range of 1-2 order of magnitude behind, but too puny to be statistically significant, either fit (model) will do. So you have to find out from context (re antialias).

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