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Spatial structure and community dynamics of arboreal ants in tropical rainforests
MOTTL, Ondřej
This thesis explores the drivers of distribution patterns and community structure of ant communities in tropical rainforest. The aim is to test how diverse arboreal ant communities are shaped by ecological gradients such as latitude, succession or forest strata, on both small and large spatial scales. This work represents a compilation of studies based on observational patterns as well as field experiments. Plot-based sampling and advanced statistics (e.g. multivariate analyses, rarefactions, and null-models) are used throughout the thesis to explore ant distribution in tropical forests. Manipulative experiments with artificial nests, and inter- and intra-behavioural trials, are used to test the hypotheses of non-random vertical species distribution (community stratification) and segregation within- and across- individual trees (ant mosaics). The effect of secondary succession on canopy ants is disentangled using unique montane forest datasets and the results are compared with previous lowland-based studies. On large geographical scale, general patterns of ant abundances are described along a latitudinal gradient and used to test the hypothesis of spatial segregation of ants with other arthropods on individual trees. The thesis results suggest that the behaviour of individual species and microhabitats are more important factors at a local scale, while forest structure and climate influence ants over larger scales.
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Structure and dynamics of arboreal ant communities along successional gradient in a mountain tropical forest of New Guinea
MOTTL, Ondřej
I analysed the structure and dynamics of a community of tropical arboreal mountain ants in Papua New Guinea over a succession gradient. There were 9 plots divided into 3 successional stages of forest (old (<50 years), middle-aged (20-30 years) and young (>13 years)). I found 24 species of arboreal ants in total. Gamma and alpha diversity differed over the successional gradient, and alpha diversity was correlated with tree size (DBH). Unexpectedly, beta diversity (number of ant species per tree) was low in middle-aged forest, i.e. it had the greatest ant species similarity between trees, probably due to forest structure (stem density and canopy connection). In contrast, the species composition of ant communities did not differ over a succession gradient, because most of the species were abundant in all forest stages. Similarly, there was also relatively little difference in composition of nest types between different successional stages. Here I have shown that succession had little impact on the structure and dynamics of tropical arboreal ant communities in high elevation, probably as a result of ants' adaptation to lower temperatures and ecological change to trophic generalists. But other factors such as absence of invasive species, food supply, and forest structure may play a significant role. In summary, local logging and shifted agriculture have relatively little impact on ant communities in mountain tropical forests. This is in contrast to similar studies from lowland rainforests and my results hence have a positive implication for tropical forest conservation of ants in mountain regions.
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