Selectively Logging Old Growth Rain Forest Twice Changes Canopy Ant Species Composition, While Conversion to Oil Palm Changes Composition and Reduces Species Richness and Diversity

Tropical forests around the world, and particularly in Southeast Asia, are being affected by anthropogenic habitat conversion and degradation. Ants, an ecologically important group in the rainforest canopy, have previously been demonstrated to be robust to a single round of selective logging, but are strongly affected by conversion to oil palm. However, the impacts of multiple rounds of selective logging on canopy ants remain unexplored. We studied the ant assemblages across a habitat gradient comprising old growth forest, twice-logged forest and oil palm plantation in Sabah, Malaysian Borneo. Canopy ants were collected using insecticide fogging across 36 sampling sites. Old growth forest and twice-logged forest had similar species richness and Shannon species diversity. These two forest habitats were significantly higher in species richness and Shannon diversity than oil palm plantation. Abundance of canopy ants was similar across all three habitats. There was a significant difference in species composition between all pairs of habitats. Leaf litter depth on the ground was positively related to ant species richness, while canopy cover was positively related to ant abundance. Hence, multiple rounds of logging cause shifts in ant species composition, while forest conversion to oil palm additionally causes reductions in ant diversity. This is of concern, since forests in Sabah and elsewhere are becoming increasingly degraded. Our results indicate that both old growth and twice-logged rain forests can be useful for conservation of canopy ants

Ant mosaics in Bornean primary rain forest high canopy depend on spatial scale, time of day, and sampling method.

Background: Competitive interactions in biological communities can be thought of as giving rise to "assembly rules" that dictate the species that are able to co-exist. Ant communities in tropical canopies often display a particular pattern, an "ant mosaic", in which competition between dominant ant species results in a patchwork of mutually exclusive territories. Although ant mosaics have been well-documented in plantation landscapes, their presence in pristine tropical forests remained contentious until recently. Here we assess presence of ant mosaics in a hitherto under-investigated forest stratum, the emergent trees of the high canopy in primary tropical rain forest, and explore how the strength of any ant mosaics is affected by spatial scale, time of day, and sampling method. Methods: To test whether these factors might impact the detection of ant mosaics in pristine habitats, we sampled ant communities from emergent trees, which rise above the highest canopy layers in lowland dipterocarp rain forests in North Borneo (38.8-60.2 m), using both baiting and insecticide fogging. Critically, we restricted sampling to only the canopy of each focal tree. For baiting, we carried out sampling during both the day and the night. We used null models of species co-occurrence to assess patterns of segregation at within-tree and between-tree scales. Results: The numerically dominant ant species on the emergent trees sampled formed a diverse community, with differences in the identity of dominant species between times of day and sampling methods. Between trees, we found patterns of ant species segregation consistent with the existence of ant mosaics using both methods. Within trees, fogged ants were segregated, while baited ants were segregated only at night. Discussion: We conclude that ant mosaics are present within the emergent trees of the high canopy of tropical rain forest in Malaysian Borneo, and that sampling technique, spatial scale, and time of day interact to determine observed patterns of segregation. Restricting sampling to only emergent trees reveals segregatory patterns not observed in ground-based studies, confirming previous observations of stronger segregation with increasing height in the canopy.Kalsum M. Yusah was funded by the South East Asia Rainforest Research Partnership (SEARRP), a Malaysian Ministry of Higher Education Fundamental Research Grant (FRG0373- STWN- 1/ 2014), and a Universiti Malaysia Sabah New Lecturer Grant Scheme grant (SLB0071- STWN- 2013). Tom M. Fayle was funded by a Czech Science Foundation standard grant (16-09427S)

Reported climate change impacts on cloud forest ants are driven by sampling bias : a critical evaluation of Warne et al. (2020)

We present a reanalysis of the study by Warne et al. (2020), where authors reported substantial changes through time in a cloud forest ant assemblage in response to climate change after a decade. We show that these changes are due to major differences between the sampling periods in terms of sampling methods and effort. We stress the need for a fully standardized methodology to distinguish true climate change effects on communities from sampling bias.Czech Science Foundation and Leverhulme Trust.http://www.wileyonlinelibrary.com/journal/btphj2022Zoology and Entomolog

Whole-ecosystem experimental manipulations of tropical forests.

Tropical forests are highly diverse systems involving extraordinary numbers of interactions between species, with each species responding in a different way to the abiotic environment. Understanding how these systems function and predicting how they respond to anthropogenic global change is extremely challenging. We argue for the necessity of 'whole-ecosystem' experimental manipulations, in which the entire ecosystem is targeted, either to reveal the functioning of the system in its natural state or to understand responses to anthropogenic impacts. We survey the current range of whole-ecosystem manipulations, which include those targeting weather and climate, nutrients, biotic interactions, human impacts, and habitat restoration. Finally we describe the unique challenges and opportunities presented by such projects and suggest directions for future experiments.This review was initiated during a symposium on ‘The effects of large scale manipulations of tropical forests on arthropod assemblages’ at the INTECOL 2013 congress, London 18–23 August 2013. T.M.F. is funded by the Australian Research Council (DP140101541), T.M.F. and R.M.E. by Yayasan Sime Darby, TMF and Y.B. by the project Biodiversity of Forest Ecosystems (CZ.1.07/2.3.00/20.0064) co-financed by the European Social Fund and the state budget of the Czech Republic, and T.M.F. Y.B. and V.N. by the Czech Science Foundation (GACR 14-32302S, 14-36098G, 14-04258S respectively). Y.B. is also supported by the Sistema Nacional de Investigacio´n of Panama. E.C.T. is supported by funds from PT SMART Research Institute and the Isaac Newton Trust, Cambridge. R.M.E. is supported by European Research Council Project number 281986. We are grateful to Maureen Fayle, Andrew Hector, Jan Leps, Scott Miller, Kalsum M. Yusah, Paul Craze, and two anonymous reviewers for advice during the drafting of the manuscript, and Jennifer Balch for additional information regarding her burning experiments.This is the final published version. It first appeared at http://www.cell.com/trends/ecology-evolution/abstract/S0169-5347%2815%2900069-5

Pairwise interactions in tropical ant communities

Ecological communities are structured by competitive, predatory, mutualistic and parasitic interactions combined with chance events. Separating deterministic from stochastic processes is possible, but finding statistical evidence for specific biological interactions is challenging. We attempt to solve this problem for ant communities nesting in epiphytic bird’s nest ferns (Asplenium nidus) in Borneo’s lowland rainforest. By recording the frequencies with which each and every single ant species occurred together, we were able to test statistically for patterns associated with interspecific competition. We found evidence for competition, but the resulting co-occurrence pattern was the opposite of what we expected. Rather than detecting species segregation—the classical hallmark of competition—we found species aggregation. Moreover, our approach of testing individual pairwise interactions mostly revealed spatially positive rather than negative associations. Significant negative interactions were only detected among large ants, and among species of the subfamily Ponerinae. Remarkably, the results from this study, and from a corroborating analysis of ant communities known to be structured by competition, suggest that competition within the ants leads to species aggregation rather than segregation. We believe this unexpected result is linked with the displacement of species following asymmetric competition. We conclude that analysing co-occurrence frequencies across complete species assemblages, separately for each species, and for each unique pairwise combination of species, represents a subtle yet powerful way of detecting structure and compartmentalisation in ecological communities.We acknowledge support from the University of Cambridge, NERC, The Royal Society South East Asia Rainforest Research Programme, Yayasan Sabah, Danum Valley Management Committee, and the Economic Planning Unit in Kuala Lumpur. TMF was supported by the Czech Science Foundation (14-32302S, 16-09427S), and the Australian Research Council (DP140101541).This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Elsevie

Living together in novel habitats: a review of land-use change impacts on mutualistic ant-plant symbioses in tropical forests

Symbiotic mutualisms between ants and plants are those in which ants provide protection from herbivory and competition from other plants, while plants provide living space in specially adapted structures, and sometimes also food. Critically, the ants inhabit the plant (symbiosis) and hence reproductive interests are often (but not always) more strongly tied than in non-symbiotic mutualisms. Ant-plant symbioses are particularly diverse in tropical forests, a habitat under severe threat from human exploitation around the world. Understanding responses of ant-plant symbiotic mutualisms to tropical habitat change is important, because both ants and their plant hosts can play key roles in the wider ecosystem. Here we summarise the current state of knowledge of the impacts of habitat change on ant-plant symbioses in tropical forests. We take as a case study the two-way by-product mutualism between bird’s nest ferns and their ant symbionts in SE Asian rain forest, and the response of this system to logging and conversion to oil palm plantation. We conclude that ant-plant symbioses are surprisingly robust to habitat change, although while the interaction often persists, some partners from pristine habitats may not survive, with their roles being filled by non-native species

Network reorganization and breakdown of an ant-plant protection mutualism with elevation.

Both the abiotic environment and the composition of animal and plant communities change with elevation. For mutualistic species, these changes are expected to result in altered partner availability, and shifts in context-dependent benefits for partners. To test these predictions, we assessed the network structure of terrestrial ant-plant mutualists and how the benefits to plants of ant inhabitation changed with elevation in tropical forest in Papua New Guinea. At higher elevations, ant-plants were rarer, species richness of both ants and plants decreased, and the average ant or plant species interacted with fewer partners. However, networks became increasingly connected and less specialized, more than could be accounted for by reductions in ant-plant abundance. On the most common ant-plant, ants recruited less and spent less time attacking a surrogate herbivore at higher elevations, and herbivory damage increased. These changes were driven by turnover of ant species rather than by within-species shifts in protective behaviour. We speculate that reduced partner availability at higher elevations results in less specialized networks, while lower temperatures mean that even for ant-inhabited plants, benefits are reduced. Under increased abiotic stress, mutualistic networks can break down, owing to a combination of lower population sizes, and a reduction in context-dependent mutualistic benefits