Testing mating systems theory in a polygynous model system: the reindeer/caribou (Rangifer tarandus)

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Over the past several decades, many models have attempted to develop a predictive framework for mating systems. However, quantifying sexual selection and testing mating systems theory in the field have proven difficult. My aim is to use an experimental approach to test the key predictions of mating systems theory. I will manipulate female density, food dispersion, and operational sex ratio (OSR) to assess how they influence mating group dynamics and mating tactics. Ungulates are excellent model systems to study the evolution of mating systems because they have the highest variability in sexual dimorphism, and because of their minimal paternal care and great variability in mating systems. I use reindeer (Rangifer tarandus) from an exceptional population where all individuals will be fitted GPS collars and manipulation is possible as my model system. Specifically we will test whether : (i) the average group size, the rate of fission, the rate of fusion, and patchiness (a measure of the degree to which females are clumped in space), increase with density; (ii) females aggregate at food patches, leading to higher average group size and patchiness in clumped than dispersed treatments; (iii) males mating strategy differs between the clumped and dispersed treatments, with resource defense in the clumped treatment and monopolization in the dispersed treatment, underlying the plasticity of mating strategies; (iv) the correlation between patchiness and the opportunity for sexual selection is positive; and whether (v) male-male aggression increases with OSR whereas female-female aggression decreases; and courtship rate decreases with OSR, because of increased male-male competition. By using a fully-controlled GPS-based population, my research will rigorously test key predictions of mating systems theory on reindeer and show whether the intensity of competition can be minimized by manipulating the local environment. The research has management implications by showing density-dependent influence on the distribution of male mating success and population productivity, and by providing information necessary for long term conservation. The work, therefore, provides insight into the mechanisms of population regulation.