Allee effects and evolution of mate search
Theoretical ecologists at the Institute of Entomology develop mathematical models to understand patterns of biodiversity as well as predict eco-evolutionary dynamics of populations exposed to a variety of environmental pressures, including diverse extinction threats. Recently published papers aim to reveal how evolution shapes mate search patterns in populations subject to Allee effects.
Figure: Population extinction probability (left) and evolution of the mate search rate (right) for some modeled ecological scenarios.
Allee effects occur in a population if individuals profit from the presence of conspecifics. They affect many applied aspects of population dynamics, including chances of invading populations to establish and spread, risk of small and threatened populations to go extinct, and risk of economically important populations to get overharvested. The enhanced difficulty of finding mates in low-density populations is the best documented pathway through which Allee effects might arise.
By means of an eco-genetic model in which populations were allowed to adapt to several density regimes, we studied the evolution of mate search. We established a mechanistic link between the mate search rate and the Allee effect, manifested by a critical population density (commonly referred to as the Allee threshold) below which the risk of population extinction abruptly increased. Density-dependent selection commonly occurred, leading to mate search rates that resulted in higher Allee thresholds in populations kept at higher densities, especially when fecundity costs were imposed on elevated mate search. This provides the first quantitative explanation for why most of the species demonstrated to possess an Allee effect are anthropogenically rare. Other model outcomes included optimizing selection, runaway selection and evolutionary suicide. Trade-offs between mate search, survival and reproductive output are key for understanding mate search strategies and their fitness consequences.
Mate search is often accompanied with behavior that can attract predators. Therefore, we also studied evolution of the rate at which male prey searched for mates under a trade-off between mate acquisition and predation risk. Contrasting two different life histories, male prey were found to either evolve the maximal mate search rate (showing no adaptive response in mating behavior to predation risk) or evolutionary bi-stability occurred. In the latter case, males evolved a relatively low mate search rate (showing an adaptive response to predation) or the maximal mate search rate. Disruptive selection was also possible. The dimorphic phase, in which fast and conspicuous male prey coexisted with slow and cryptic ones, was however but a transient in evolutionary dynamics as one branch went extinct while the other evolved towards the maximal mate search rate.
Berec L., Kramer A. M., Bernhauerová V., Drake J. M. (2018) Density-dependent selection on mate search and evolution of Allee effects. Journal of Animal Ecology 87: 24-35; doi: 10.1111/1365-2656.12662
Kramer A. M., Berec L., Drake J. M. (2018) Allee effects in ecology and evolution. Journal of Animal Ecology 87: 7-10; doi: 10.1111/1365-2656.12777
Kuparinen A. (2018) The mechanistic basis of demographic Allee effects: the search for mates. Journal of Animal Ecology 87: 4-6; doi: 10.1111/1365-2656.12774
Berec L., Bernhauerová V., Boldin B. (2018) Evolution of mate-finding Allee effect in prey. Journal of Theoretical Biology 441: 9-18; doi: 10.1016/j.jtbi.2017.12.024
