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ScienceWeek
EVOLUTIONARY BIOLOGY: ON THE NICHE-CONSTRUCTION CONTROVERSY
The following points are made by Kevin N. Laland et al (Nature 2004 429:609):
1) Evolutionary biology has always generated vigorous debate, from the arguments about lamarckian inheritance during the 1900s, to the more recent disputes over punctuated equilibria and group selection. The latest spat -- a storm in a teacup compared with these earlier controversies -- concerns the seemingly prosaic observation that the activities of organisms bring about changes in their environments -- a process known as "niche construction". In January 2004, ecologist John Vandermeer described the niche-construction perspective as "a major breakthrough", yet an earlier review by Laurent Keller (Nature 2003 425:769) dismissed the niche construction perspective as hyperbole, and evolutionary biologist Richard Dawkins warns of its "pernicious" reasoning in a forthcoming article. It is a subject that typically provokes strong and polarized responses. What is the fuss about?
2) At the heart of the controversy lies the nature of causality in evolution. Adaptation is conventionally seen as a process by which natural selection shapes organisms to fit pre-established environmental "templates". The causal arrow points in one direction only: it is environments, the source of selection, that determine the features of living creatures.
3) Yet it is also obvious that organisms bring about changes in environments. Numerous animals manufacture nests, burrows, holes, webs and pupal cases. Plants change the levels of atmospheric gases and modify nutrient cycles. Fungi decompose organic matter, and bacteria engage in decomposition and nutrient fixation. The standard view of evolution does not deny this, but treats niche construction as no more than the product of selection.
4) Conversely, from the niche-construction perspective, evolution is based on networks of causation and feedback. Organisms drive environmental change and organism-modified environments subsequently select organisms. The argument that niche construction does not play a causal role in evolution because it is partly a product of natural selection, makes no more sense than would the counter-proposal that natural selection can be disregarded because it is partly a product of niche construction.(1-4)
References (abridged):
1. Jones, C. G. et al. Ecology 78, 1946-1957 (1997)
2. Laland, K. N., Odling-Smee, J. & Feldman, M. W. Proc. Natl Acad. Sci. USA 96, 10242-10247 (1999)
3. Odling-Smee, J., Laland, K. N. & Feldman, M. W. Niche Construction. The Neglected Process in Evolution. Monographs in Population Biology 37 (Princeton Univ. Press, Princeton, 2003)
4. Vandermeer, J. Science 303, 472-474 (2004)
Nature http://www.nature.com/nature
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Related Material:
EVOLUTIONARY CONSEQUENCES OF NICHE CONSTRUCTION
Notes by ScienceWeek
In ecology, the term "ecosystem" refers to a functioning unit of nature that combines biotic communities and the abiotic environment with which they interact, and the term "niche" refers to the physical location of an organism and the function of an organism within an ecosystem.
There is an increasing recognition that all organisms modify their environments, a process called "niche construction" (also called "ecosystem engineering"). Such modifications can have profound effects on the distribution and abundance of organisms, the influence of *keystone species, the control of energy and material flows, migrating species residence and return times, *ecosystem resilience, and specific *trophic relationships. But the consequences of environmental modification by organisms are not restricted to ecology, and organisms can affect both their own and each other's evolution by modifying sources of natural selection in their environments.
The following points are made by K.N. Laland et al (Proc. Natl. Acad. Sci. 1999 96:10242):
1) The authors present an analysis of the evolutionary consequences of niche construction using a *population genetics model that extends earlier analyses by allowing resource distributions to be influenced both by niche construction and by independent processes of renewal and depletion.
2) The authors report their analysis confirms that niche construction can be a potent evolutionary agent by generating selection that leads to the fixation of otherwise deleterious *alleles, supporting stable *polymorphisms where none are expected, eliminating what would otherwise be stable polymorphisms, and generating unusual evolutionary dynamics.
3) The authors suggest that even small amounts of niche construction, or niche construction that only weakly affects resource dynamics, can significantly alter both ecological and evolutionary patterns.
4) The authors conclude: "Unlike standard evolutionary theory, the present approach is equally applicable to both population-community ecology and ecosystem-level ecology, which may eventually make it easier to reconcile these two ecological subdisciplines under the rubric of an extended evolutionary theory that includes niche construction."
Proc. Nat. Acad. Sci. http://www.pnas.org
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Notes by ScienceWeek:
keystone species: In this context, the term "keystone species" refers to organisms that play dominant roles in an ecosystem, affecting many other organisms. For example, the removal of a keystone predator from an ecosystem usually causes a reduction of species diversity among its former prey.
ecosystem resilience: The "resilience" of an ecosystem is the ability of the ecosystem to return to its original or steady-state condition after a disturbance.
trophic relationships: In general, the term "trophic" refers to nutrition or food. (The term should not be confused with "tropic" [from "tropism"; e.g., a "tropic" response], which refers to an involuntary or reflex turning by a cell, plant, or animal in response to a stimulus.)
population genetics model: In general, "population genetics" is the study of the genetic composition of populations. Population geneticists attempt to estimate gene frequencies and detect the selective influences that determine these gene frequencies in natural populations. Mathematical models in population genetics examine the interaction of factors such as selection, population size, mutation, and migration on the fixation and loss of linked and unlinked genes.
alleles: (allelomorph) An "allele" is one of two or more forms of a given gene that control a particular characteristic, with the alternative forms occupying corresponding loci on homologous chromosomes. Different alleles usually produce different characteristics in an organism, e.g., brown versus blue eyes.
polymorphisms: In this context, the term "polymorphism" refers to the existence of more than one form or type in a species, beyond simple gender differences. For example, social insects such as honeybees (with queens, drones, and workers) demonstrate polymorphisms.
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Related Material:
EVOLUTION: ADAPTIVE RADIATION IN A HETEROGENEOUS ENVIRONMENT
Notes by ScienceWeek
The term "adaptive radiation" refers to the rapid evolution of one or a few forms into many different species that occupy different habitats within a new geographical area. The marsupial radiation in Australia illustrates the process: when marsupials were protected from competition with placental mammals by the isolation of the continent, the process led to an entire array of species with widely divergent functions, from herbivores to carnivores.
The following points are made by Rainey and Travisano (Nature 1998 394:69):
1) The authors report an investigation of the role of ecological opportunity and competition in driving the genetic diversification associated with adaptive radiation. The form studied was the common aerobic bacterium Pseudomonas fluorescens, which evolves rapidly under novel environmental conditions to generate a large repertoire of mutants.
2) As bacteria reproduce asexually, identical populations can be established from a single genotype, and all subsequent variation is therefore generated de novo by mutation.
3) The authors report that when provided with ecological opportunity, identical populations of P. fluorescens diversify morphologically, but when ecological opportunity is restricted, there is no such divergence.
4) In spatially structured environments, the evolution of variant forms follows a predictable sequence, with competition among the newly evolved niche-specialists apparently maintaining this variation.
5) The authors suggest their results demonstrate that the elementary processes of mutation and selection alone are sufficient to promote rapid proliferation of new designs, and that their results support the theory that trade-offs in competitive ability drive adaptive radiation.
Nature http://www.nature.com/nature
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