Sex difference and Allee effects shape the dynamics of sex-structured invasions

• Published in: The Journal of animal ecology 2018-01, Vol.87 (1), p.36-46
• Main Authors: Shaw, Allison K., Kokko, Hanna, Neubert, Michael G.
• Format: Article
• Language: English
• Subjects: Complications; Demographics; Dispersal; Dispersion; Females; Gender aspects; Gender differences; integrodifference equations; invasion speed; Invasions; Life history; Males; mate‐finding Allee effect; Mating behavior; mating functions; Modelling; Population; Population density; Populations; Reproduction (biology); Sex; Sex differences; Sex ratio; Sexes; sex‐biased dispersal; spatial spread; Special Feature: Allee effects in ecology and evolution
• ISSN: 0021-8790; 1365-2656
• DOI: 10.1111/1365-2656.12658

1. The rate at which a population grows and spreads can depend on individual behaviour and interaction with others. In many spwcies with two sexes, males and femeal differ in key life-history traits (e.g. growth, survival and dispersal), which can scale up to affect population rates of growth and spread. In sexually reproducing species, the mechanics of locating mates and reproducing successfully introduce further complications for predicting the invasion speed (spread rate), as both can change nonlinearly with density. 2. Most models of population spread are based on one sex, or include limited aspects of sex differences. Here we ask whether and how the dynamics of finding mates interact with sex-specific life-history traits to influence the rate of population spread. 3. We present a hybrid approach for modelling invasions of populations with two sexes that links individual-level mating behaviour (in an individual-based model) to population-level dynamics (in an integrodifference equation model). 4. We find that limiting the amount of time during which individuals can search for mates causes a demographic Allee effect which can slow, delay, or even prevent an invasion. Furthermore, any sex-based asymmetries in life history or behaviour (skewed sex ratio, sex-biased dispersal, and sex-specific mating behaviours) amplify these effects. In contrast, allowing individuals to mate more than once ameliorates these effects, enabling polygynandrous populations to invade under conditions where monogamously mating populations would fail to establish. 5. We show that details of individuals' mating behaviour can impact the rate of population spread. Based on our results, we propose a stricter definition of a matefinding Allee effect, which is not met by the commonly used minimum mating function. Our modelling approach, which links individual- and population-level dynamics in a single model, may be useful for exploring other aspects of individual behaviour that are thought to impact the rate of population spread.