The relevance of ants as seed rescuers of a primarily bird-dispersed tree in the Neotropical cerrado savanna |
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Authors: | Alexander V Christianini Paulo S Oliveira |
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Institution: | (1) Redpath Museum, McGill University, 859 Sherbrooke Street West, Montreal, QC, H3A 2K6, Canada;(2) Present address: Department of Biology, Queen’s University, Kingston, ON, K7L 3N6, Canada;(3) Department of Biology, University of California, 900 University Avenue, Riverside, CA 92521, USA |
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Abstract: | Sex ratios can influence mating behaviour, population dynamics and evolutionary trajectories; yet the causes of natural sex
ratio variation are often uncertain. Although secondary (birth) sex ratios in guppies (Poecilia reticulata) are typically 1:1, we recorded female-biased tertiary (adult) sex ratios in about half of our 48 samples and male-biased
sex ratios in none of them. This pattern implies that some populations experience male-biased mortality, perhaps owing to
variation in predation or resource limitation. We assessed the effects of predation and/or inter-specific resource competition
(intraguild predation) by measuring the local catch-per-unit-effort (CPUE) of species (Rivulus killifish and Macrobrachium prawns) that may differentially prey on male guppies. We assessed the effects of resource levels by measuring canopy openness
and algal biomass (chlorophyll a concentration). We found that guppy sex ratios were increasingly female-biased with increasing CPUE of Macrobrachium, and perhaps also Rivulus, and with decreasing canopy openness. We also found an interaction between predators and resource levels in that the effect
of canopy openness was greatest when Macrobrachium CPUE was highest. Our study thus also reveals the value of simultaneously testing multiple environmental factors that may
drive tertiary sex ratio variation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Life history Male-biased sex ratio Predation Resource limitation Sex-biased mortality |
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