Negative Frequency-dependent Mimicry Governs Seasonal Population Dynamics of Batesian Mimics

Abstract

Seasonal changes in climate, resources, and trophic interactions jointly shape prey population dynamics in ecological systems. In monsoon-driven tropical and subtropical landscapes, prey populations cycle between cool, wet, favourable periods during the rainy seasons and hot/cold, dry and sub-optimal conditions outside the rainy seasons, with resource availability and predation risk changing across seasons of the year. Defensive strategies and species interactions such as aposematism and Batesian mimicry are expected to interact with seasonal changes in resource availability and predation risk in determining population dynamics of prey species. Here we study population dynamics of mimetic butterfly community members using a 12-year long-term dataset from a subtropical urban forest in peninsular India. Our results show that climate and species interactions differentially influence population dynamics of different functional categories in mimetic butterfly communities, i.e., of aposematic species, mimetic and non-mimetic forms of mimetic species, and close relatives treated as ecological and phylogenetic contrasts. Population dynamics of non-mimetic species and forms were predominantly influenced by climate parameters such as temperature and precipitation, whereas population dynamics of mimics were more deeply impacted by mimetic interactions. Population dynamics of non-mimetic and mimetic forms of the same species showed distinct decoupling, with population dynamics of non-mimetic forms being similar to their non-mimetic relatives (phylogenetic contrasts). On the other hand, population dynamics of aposematic species and mimetic forms/species followed the predictions of negative frequency dependence and phase-shifting in mimicry theory: (a) mimetic forms/species were less abundant than their Batesian models, (b) the harmonic mean of populations of Batesian models influenced the upper limit of relative frequency of mimetic forms/species to a greater degree in these continuously breeding, seasonally fluctuating populations, and (c) populations of Batesian mimics peaked after population peaks of their Batesian models. These results reveal that climate and species interactions differentially determine population dynamics of prey species by functional categories at the community level, rather than by species identity and individual species attributes and resource demands.