PARENT SESSION
Oral Session # 90: Ecological Theory III: Modeling: Populations; Disease.
Presiding: K Dixon
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 102.
Lost in time, lonely and single: Reproductive asynchrony as a mechanism of the Allee effect.
Calabrese, Justin*,1, Fagan, William1, 1 Department of Biology, University of Maryland, College Park, MD
ABSTRACT- Identifying linkages between life history traits and small population processes is essential to the effective conservation of threatened and endangered species. Reproductive asynchrony, which occurs when individuals are reproductively active for only a portion of the population-level breeding period, has not yet been analyzed in this manner. Though asynchrony has generally been considered an advantageous bet-hedging strategy in a temporally unpredictable environment, we explored the dynamic consequences of reproductive asynchrony as a density-dependent life history trait. We first compiled empirical data on reproductive timing for a variety of insects and dioecious annual plants to restrict our mathematical analyses to realistic levels of asynchrony. We then used a general model of reproductive timing to quantify the temporal overlap of opposite-sex individuals and to simulate the dynamics of theoretical populations over a range of initial population densities and levels of asynchrony. This approach allowed us to examine quantitatively how asynchrony affects extinction risk. Finally, we considered how protandry, a life history strategy that often accompanies asynchrony, modulates the population-level effects of reproductive asynchrony. We found that asynchrony reduces a female's probability of mating by: 1) decreasing the number of males a female overlaps with, 2) decreasing the average probability of mating per male/female pair that do overlap, and 3) leaving some females completely isolated in time. This loss of reproductive potential leads to extinction via an Allee effect at low population density. In all cases, protandry exacerbates the loss of reproductive potential, making populations exhibiting both asynchrony and protandry more susceptible to extinction. Reproductive asynchrony, acting either alone or in concert with protandry, should therefore be recognized as a mechanism of the Allee effect and be included among the suite of life history characters analyzed when determining a species' extinction risk at low population density.
Key words: protandry, extinction risk, reproductive asynchrony, Allee effect