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

NICOLÁS BONEL; LEANDRO HÜNICKEN; FRANCISCO SYLVESTER

Rennes

Conferencia; International Conference on Ecological Sciences of the French Society of Ecology and Evolution; 2018

Société Française d'Écologie et d'Évolution

In newly invaded habitats, individuals are forced to rapidly respond to novel stressful con- ditions atthe expanding front of their distribution, where differing selective pressures favor the evolution of lifehistorytraits that increase the rate of population growth. Freshwater clams of the genus Corbicula aresuccessful global invaders, but the ecological and evolutionary factors that drive their range expansionremain poorly understood. We conducted an exhaustive search for peer-reviewed articles providingenough information on Corbicula to estimate population density, population growth rate (per capitarate of increase), individual growth rate, age at first reproduction, and time since populationfoundation. We retained 16 out of 223 studies, covering 19 invasive populations of Corbicula fromdifferent ecosystems worldwide. We tested whether (i) recently established populations (assumed torepresent the invasion front) occur at lower densities than older populations, (ii) populations? growthrates are higher at initial low densities and decrease as densities build up, and (iii) populations withreduced per capita rate of increase are constituted by clams exhibiting faster growth, as predicted bytheory. We found that newly established populations showed lower abundance compared to longestablish ones. This is consistent with front-edge populations occurring at low conspecific densitiesbelow the carrying capacity. We also found that Corbicula exhibited a density-independentpopulation growth, which suggest that density of this invasive species is mainly regulated byabiotic factors rather than biotic ones. Populations with a reduced per capita rate of increasewere 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, theseresults support theoretical predictions that front-edge populations experience strong r -selection, favoring early reproduction as an effective mechanism to increase populationgrowth rate, prevent stochastic extinction, and accelerate range expansion.