Spatial covariance of herbivorous and predatory guilds of forest canopy arthropods along a latitudinal gradient

In arthropod community ecology, species richness studies tend to be prioritised over those investigating patterns of abundance. Consequently, the biotic and abiotic drivers of arboreal arthropod abundance are still relatively poorly known. In this cross-continental study, we employ a theoretical framework in order to examine patterns of covariance among herbivorous and predatory arthropod guilds. Leaf-chewing and leaf-mining herbivores, and predatory ants and spiders, were censused on > 1000 trees in nine 0.1 ha forest plots. After controlling for tree size and season, we found no negative pairwise correlations between guild abundances per plot, suggestive of weak signals of both inter-guild competition and top-down regulation of herbivores by predators. Inter-guild interaction strengths did not vary with mean annual temperature, thus opposing the hypothesis that biotic interactions intensify towards the equator. We find evidence for the bottom-up limitation of arthropod abundances via resources and abiotic factors, rather than for competition and predation.publishedVersio

Structure and dynamics of arboreal ant communities along successional gradient in a mountain tropical forest of New Guinea

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 (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

Detection of UV- fluorescent- marked prey in the guts of predators and scavengers, dynamic of scavenging in a model experiment.

Scavenging represents an important ecological process in terms of nutrition circulation and food web interactions. This thesis deals with using of UV-fluorescent dye in a field experiment based on method developed in laboratory to assess whether this method is applicable for identification of scavengers under field conditions. Field experiment was conducted in Mokre, Ceske Budejovice, Czech Republic. This laboratory part has been made at the Faculty of Science, University of South Bohemia, Ceske Budejovice, Czech Republic

Spatial structure and community dynamics of arboreal ants in tropical rainforests

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

Data from: Experiments with artificial nests provide evidence for ant community stratification and nest site limitation in a tropical forest

Ants are dominant in tropical forests and many species nest in hollow cavities. The manner in which species are vertically stratified in these complex habitats is not known, with lack of nest sites being proposed to limit ant populations. Here we assess ant community stratification and nest site limitation in a lowland rainforest in New Guinea using experimental addition of artificial bamboo nests of two cavity sizes (small: ~12 mm. large: ~32 mm diameter) placed at ground level, in the understorey, and in the canopy. We also conducted a pilot experiment to test the utility of nest translocation. Nests were checked for occupancy after 10 weeks and half of the occupied nests were then translocated between forest plots, while keeping same vertical position. Occupancy of small nests was much higher in the understorey and canopy than at ground level (~75% versus ~25%). Translocation was successful, as a majority of nests was inhabited by the same species before and after translocation and there was no impact of translocation to a different plot compared to the control, except for a reduction in colony size at ground level. Our experiment demonstrates a vertical stratification in community composition of ants nesting in hollow dead cavities and shows that these ants are more nest-site limited in the higher strata than at ground level. Use of small artificial cavities has great potential for future experimental studies, especially for those focused on arboreal ants, as occupancy is high and translocation does not negatively affect their colony size

Mottl-Ecosphere-TropicalArborealAnts_TreeFelling_PNG2019

Datafile containing information about arboreal ants from succession series in the montane tropical forest in Papua New Guinea. Data were obtained using felling of all trees with DBH>5 and collection of all foragers and nests. In total, 9 plot of 0.1ha in 3 successional stages were sampled. List AllRecords contains information about all tree and presence/absence information of ant species. In addition, there is information about environmental variables for each tree. List NestRecords contains information about the number of ant nests of each ant species in each tree and environmental variables linked to them

Global acceleration in rates of vegetation change over the past 18,000 years

Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago

Spatial covariance of herbivorous and predatory guilds of forest canopy arthropods along a latitudinal gradient

In arthropod community ecology, species richness studies tend to be prioritised over those investigating patterns of abundance. Consequently, the biotic and abiotic drivers of arboreal arthropod abundance are still relatively poorly known. In this cross-continental study, we employ a theoretical framework in order to examine patterns of covariance among herbivorous and predatory arthropod guilds. Leaf-chewing and leaf-mining herbivores, and predatory ants and spiders, were censused on > 1000 trees in nine 0.1 ha forest plots. After controlling for tree size and season, we found no negative pairwise correlations between guild abundances per plot, suggestive of weak signals of both inter-guild competition and top-down regulation of herbivores by predators. Inter-guild interaction strengths did not vary with mean annual temperature, thus opposing the hypothesis that biotic interactions intensify towards the equator. We find evidence for the bottom-up limitation of arthropod abundances via resources and abiotic factors, rather than for competition and predation

Global acceleration in rates of vegetation change over the past 18,000 years

Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biodiversity change demonstrated in ecological datasets from the past century began millennia ago

Quantitative assessment of plant-arthropod interactions in forest canopies: A plot-based approach.

Research on canopy arthropods has progressed from species inventories to the study of their interactions and networks, enhancing our understanding of how hyper-diverse communities are maintained. Previous studies often focused on sampling individual tree species, individual trees or their parts. We argue that such selective sampling is not ideal when analyzing interaction network structure, and may lead to erroneous conclusions. We developed practical and reproducible sampling guidelines for the plot-based analysis of arthropod interaction networks in forest canopies. Our sampling protocol focused on insect herbivores (leaf-chewing insect larvae, miners and gallers) and non-flying invertebrate predators (spiders and ants). We quantitatively sampled the focal arthropods from felled trees, or from trees accessed by canopy cranes or cherry pickers in 53 0.1 ha forest plots in five biogeographic regions, comprising 6,280 trees in total. All three methods required a similar sampling effort and provided good foliage accessibility. Furthermore, we compared interaction networks derived from plot-based data to interaction networks derived from simulated non-plot-based data focusing either on common tree species or a representative selection of tree families. All types of non-plot-based data showed highly biased network structure towards higher connectance, higher web asymmetry, and higher nestedness temperature when compared with plot-based data. Furthermore, some types of non-plot-based data showed biased diversity of the associated herbivore species and specificity of their interactions. Plot-based sampling thus appears to be the most rigorous approach for reconstructing realistic, quantitative plant-arthropod interaction networks that are comparable across sites and regions. Studies of plant interactions have greatly benefited from a plot-based approach and we argue that studies of arthropod interactions would benefit in the same way. We conclude that plot-based studies on canopy arthropods would yield important insights into the processes of interaction network assembly and dynamics, which could be maximised via a coordinated network of plot-based study sites