Abstract
Anthropogenic disturbance and the spread of non-native species disrupt natural communities, but also create novel interactions between species. By-product mutualisms, in which benefits accrue as side effects of partner behaviour or morphology, are often non-specific and hence may persist in novel ecosystems. We tested this hypothesis for a two-way by-product mutualism between epiphytic ferns and their ant inhabitants in the Bornean rain forest, in which ants gain housing in root-masses while ferns gain protection from herbivores. Specifically, we assessed how the specificity (overlap between fern and ground-dwelling ants) and the benefits of this interaction are altered by selective logging and conversion to an oil palm plantation habitat. We found that despite the high turnover of ant species, ant protection against herbivores persisted in modified habitats. However, in ferns growing in the oil palm plantation, ant occupancy, abundance and species richness declined, potentially due to the harsher microclimate. The specificity of the fern–ant interactions was also lower in the oil palm plantation habitat than in the forest habitats. We found no correlations between colony size and fern size in modified habitats, and hence no evidence for partner fidelity feedbacks, in which ants are incentivised to protect fern hosts. Per species, non-native ant species in the oil palm plantation habitat (18 % of occurrences) were as important as native ones in terms of fern protection and contributed to an increase in ant abundance and species richness with fern size. We conclude that this by-product mutualism persists in logged forest and oil palm plantation habitats, with no detectable shift in partner benefits. Such persistence of generalist interactions in novel ecosystems may be important for driving ecosystem functioning.Electronic supplementary materialThe online version of this article (doi:10.1007/s00442-014-3208-z) contains supplementary material, which is available to authorized users.
Highlights
When humans severely alter the environment, ecologically stable, novel ecosystems can be created (Hobbs et al 2009)
Community similarity between fern and litter ants was significantly higher in oil palm plantation [t tests: primary forest–oil palm plantation: N = 20, For common ant species (≥5 colonies in a habitat), there was no relationship between colony size and fern size, larger ferns supported higher total abundances of ants (Fig. 4a)
Larger ferns were inhabited by more species of ant (Linear model: t3,56 = 5.60, P < 0.001; Fig. 4b), and ferns in primary forest did not differ from those in logged forest or oil palm plantation in this relationship
Summary
When humans severely alter the environment, ecologically stable, novel ecosystems can be created (Hobbs et al 2009). The network of interactions between species can be significantly altered (Tylianakis et al 2010), with the loss of individual species leading either to co-extinctions of species reliant on each other (Koh et al 2004) or increases in abundance of species whose competitors or natural enemies disappear (Ritchie and Johnson 2009). These processes are expected to change the adaptive landscape in newly formed ecosystems, with shifts in the costs and benefits of associations between specific partner species (Aslan et al 2013). The interaction could persist under two scenarios: (1) a subset of the remaining partners continue to interact, or (2) invading non-natives fill the roles vacated by locally extinct partners
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