Factors affecting the Coexistence of specialist and generalist Species

The coexistence of specialists and generalists in metacommunity is mediated by species traits and environmental factors

Differences between specialist and generalist species

Generalists such as raccoons are sometimes able to adapt to urban environments.

Animal species reside on a scale with “generalist” on one end and “specialist” on the other. Specialists can live only in a narrow range of conditions: diet, climate, camouflage, etc. Generalists are able to survive a wide variety of conditions and changes in the environment: food, climate, predators, etc.

Specialists thrive when conditions are just right. They fulfill a niche and are very effective at competing with other organisms. They have good mechanisms for coping with “known” risks. But when the specific conditions change, they are much more likely to go extinct. Generalists respond much better to changes/uncertainty.

A specialist animal, the koala only lives in and eats the leaves of eucalyptus trees.

Specialization puts species at extreme risk

Human activities and environmental changes are driving many species to extinction. Species that exhibit a narrow environmental tolerance (specialist species) are particularly vulnerable and are currently declining worldwide. Their extinction strongly modifies the species composition of ecosystems. We can therefore observe the thriving of species with wide environmental tolerance (generalist species). For the maintenance of biodiversity and for the design of adapted management strategies it is crucial to understand which factors drive the maintenance of specialist species in ecosystems.

L. Büchi and S. Vuilleumier of the University of Lausanne in Switzerland have analyzed a model to identify the factors impacting the coexistence of specialist and generalist species. Two key factors have a drastic influence on the species composition of communities: species’ dispersal ability and the number of interacting species. Low dispersal limits the spread of specialist species, as their narrow environmental tolerance creates barriers that prevent them from reaching other favorable habitats. In contrast, it favors generalist species which are able to disperse gradually to neighboring habitats thanks to their higher environmental tolerance. When the number of interacting species is large, more specialist species are found as they have a strong advantage over generalist species in their habitats. Ecosystem loss and fragmentation might then drive specialist species to extinction as these factors limit species dispersal and reduce the number of species in ecosystems.

This work elucidates how species with different environmental tolerances can coexist together. In addition, it provides new insights into the design of conservation and management strategies. In particular, the future survival of specialist species relies on the conservation of whole ecosystems and the maintenance of high connectivity between them.