Picky Females Promote Diversity
M/'Gonigle, L. K., R. Mazzucco, et al. (2012). "Sexual selection enables long-term coexistence despite ecological equivalence." Nature advance online publication.
Picky Females Promote Diversity
The new Nature study on "picky females" may explain how cichlids, a fish found in Lake Victoria in Africa, can coexist in high diversity in the same habitat. (Credit: Ole Seehausen, Fish Ecology and Evolution, Eawag, Switzerland)
ScienceDaily (Apr. 1, 2012) — Picky females play a critical role in the survival and diversity of species, according to a Nature study by researchers from the University of British Columbia and the International Institute for Applied Systems Analysis (IIASA) in Austria.
To date, biodiversity theories have focused on the role played by adaptations to the environment: the species best equipped to cope with a habitat would win out, while others would gradually go extinct. The new study presents the first theoretical model demonstrating that selective mating alone can promote the long-term coexistence of species -- such as frogs, crickets, grasshoppers and fish -- that share the same ecological adaptations and readily interbreed.
"The focus on ecological adaptation has failed to explain much of the biodiversity we see right before our eyes," says the study's first author Leithen M'Gonigle, a postdoctoral fellow at the University of California at Berkeley, who developed this work while a PhD candidate at UBC.
"Our model shows that species can stably coexist in the same habitat as long as two simple conditions are met. First, the distribution of resources they use must not be uniform, so that groups of females with different mate preferences can occupy different resource hotspots. Second, females must pay a cost for being choosy, through reduced survival or fecundity," says M'Gonigle.
"Resource distributions are never uniform over space, even in seemingly homogeneous habitats like grasslands and lakes," says co-author Ulf Dieckmann, leader of the Evolution and Ecology Program at IIASA.
"By being picky, females almost always suffer a cost, because they spend energy either to find a preferred mate or to avoid an undesirable one," says UBC zoologist and co-author Sarah Otto, Canada Research Chair in Theoretical and Experimental Evolution and a 2011 fellow of the John D. and Catherine T. MacArthur Foundation.
"These costs turn out to be crucial for reinforcing species boundaries," says IIASA scholar and co-author Rupert Mazzucco. "Because they prevent females with a particular preference from invading areas dominated by males they find unattractive."
Overcoming the long-held belief that species can stably coexist only if they differ in their ecological adaptations, this study is opening up new vistas on understanding and protecting the grandeur of biological diversity, according to the authors.
Empirical data indicate that sexual preferences are critical for maintaining species boundaries1, 2, 3, 4, yet theoretical work has suggested that, on their own, they can have only a minimal role in maintaining biodiversity5, 6, 7, 8, 9. This is because long-term coexistence within overlapping ranges is thought to be unlikely in the absence of ecological differentiation9. Here we challenge this widely held view by generalizing a standard model of sexual selection to include two ubiquitous features of populations with sexual selection: spatial variation in local carrying capacity, and mate-search costs in females. We show that, when these two features are combined, sexual preferences can single-handedly maintain coexistence, even when spatial variation in local carrying capacity is so slight that it might go unnoticed empirically. This theoretical study demonstrates that sexual selection alone can promote the long-term coexistence of ecologically equivalent species with overlapping ranges, and it thus provides a novel explanation for the maintenance of species diversity.
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