Life at the expanding front: Freshwater invasive clams reproduce earlier in populations with reduced per capita rate of increase

FRANCISCO SYLVESTER; NICOLÁS BONEL; LEANDRO HÜNICKEN

Rennes

Congreso; SFECOLOGIE 2018 - International Conference On Ecological Sciences; 2018

French Ecological Society

In newly invaded habitats, individuals are forced to rapidly respond to novel stressful con- ditions at the expanding front of their distribution, where differing selective pressures favor the evolution of life- history traits that increase the rate of population growth. Freshwater clams of the genus Corbicula are successful global invaders, but the ecological and evolutionary factors that drive their range expansion remain poorly understood. We conducted an exhaustive search for peer-reviewed articles providing enough information on Corbicula to estimate population density, population growth rate (per capita rate of increase), individual growth rate, age at first reproduction, and time since population foundation. We retained 16 out of 223 studies, covering 19 invasive populations of Corbicula from different ecosystems worldwide. We tested whether (i) recently established populations (assumed to represent the invasion front) occur at lower densities than older populations, (ii) populations? growth rates are higher at initial low densities and decrease as densities build up, and (iii) populations with reduced per capita rate of increase are constituted by clams exhibiting faster growth, as predicted by theory. We found that newly established populations showed lower abundance compared to long establish ones. This is consistent with front-edge populations occurring at low conspecific densities below the carrying capacity. We also found that Corbicula exhibited a density-independent population growth, which suggest that density of this invasive species is mainly regulated by abiotic factors rather than biotic ones. Populations with a reduced per capita rate of increase were composed by clams with faster growth which, in turn, reach breeding size earlier (i. e., at a younger age) compared to those from higher populations growth rate. Together, these results support theoretical predictions that front-edge populations experience strong r - selection, favoring early reproduction as an effective mechanism to increase population growth rate, prevent stochastic extinction, and accelerate range expansion.