2016 Denslow & Ashton Prizes (Outstanding Papers in @Biotropica)
Every year Biotropica’s Editorial Board selects the recipients of the Denslow and Ashton Prizes, which recognize two outstanding papers published in our journal in the previous calendar year (prior recipients can be found here). Criteria for selecting the papers to receive these awards include clarity of presentation, a strong basis in natural history, well-planned experimental or sampling design, and the novel insights gained into critical processes that influence the structure, functioning, or conservation of tropical systems.
I am pleased to announce the articles selected of the 2016 Denslow and Ashton Prizes are:
Julie S. Denslow Prize (for the Outstanding Paper in Biotropica): Yoshinori Nakazawa and Andrew Townsend Peterson. 2015. Effects of Climate History and Environmental Grain on Species’ Distributions in Africa and South America. Biotropica, 47: 292–299.
Peter Ashton Prize (for the Outstanding Paper in Biotropica by a Student): Franziska Peter, Dana G. Berens, Graham R. Grieve and Nina Farwig. 2015). Forest Fragmentation Drives the Loss of Insectivorous Birds and an Associated Increase in Herbivory. Biotropica, 47: 626–635.
In the following essays, the authors of the award-winning articles describe what captured their attention, what inspired the study, and how they hope the work will inspire other researchers. We hope you enjoy these insights into the process that resulted in such novel and interesting work, and congratulations to our 2016 award winners on behalf of the Editorial Board and The Association for Tropical Biology and Conservation.
Emilio M. Bruna, Editor-in-Chief
University of Florida
2016 Julie Denslow Prize
For the Outstanding Paper in Biotropica
Yoshinori Nakazawa and Andrew Townsend Peterson. 2015. Effects of Climate History and Environmental Grain on Species’ Distributions in Africa and South America. Biotropica, 47: 292–299.
Climate changes during the Pleistocene produced shifts, reductions, and expansions of biomes that, in turn, have been hypothesized to have driven speciation and extinction and shaped patterns of biodiversity. Here, we explore effects of Late Pleistocene climatic changes on environmentally and geographically cohesive areas mimicking species’ distributions. We analyzed persistence of these ‘species’ over the transition from the warm Last Interglacial period to the cool Last Glacial Maximum period to warm present-day conditions, for four levels of environmental restriction (5, 10, 15 and 20% of overall variation; akin to niche breadths). African environments were overall much less conserved over these periods than those of South America, matching diversity contrasts between the two continents. Results thus indicate that biodiversity patterns relate closely to historical patterns of environmental grain and their stability through time; this view is a step toward an integral understanding of the role of environmental and geographic factors in the process of biological diversification.
What Processes Generate Tropical Biodiversity Patterns?
Centers for Disease Control and Prevention
Atlanta, Georgia, USA
Nakazawa and Peterson (2015) presented a series of analyses of how simple sets of processes, such as ecological niche requirements, real-world landscapes, and changing climates, act to generate patterns of biodiversity. This work is predicated on sampling environments across Africa and South America, and assessing their stability through the last two major climate shifts at the end of the Pleistocene. This contribution adds to a growing body of research that gets at how biodiversity patterns may be generated.
The literature regarding biodiversity patterns at global and regional scales frequently invokes or explores diverse biotic and abiotic mechanisms that may generate those patterns, including energy availability, interspecific interactions, species packing, speciation-extinction balance, etc. (Gaston 2000, Willig et al. 2003, Ricklefs 2004, Orme et al. 2006, Storch et al. 2006). Different authors assessing different taxa in different geographic contexts invariably emphasize different causal factors. A recent paper by an impressive list of authors recently sketched a “general simulation model” that would include each of the relevant factors in an overall simulation framework and that would allow exploration of important drivers (Gotelli et al. 2009), although this model has not, apparently, been implemented as of yet.
More generally, this body of work began with novel analyses by Robert Colwell and Thiago Rangel (Rangel et al. 2007), which explored models of biodiversity and biogeography, based on range fragmentation, speciation, and extinction processes, and emphasized abiotic niche characteristics as key drivers of biodiversity patterns. Further recent work (Kleidon et al. 2009, Reu et al. 2011) explored the survivability of ‘species’ using a diversity of niche characteristics, and again discovered a crucial role of tolerances of abiotic conditions in determining how much biological diversity can be maintained at a site. These initial steps laid a foundation of insights that suggested that realistic biodiversity patterns could be generated from simple processes not requiring complex explanations based on community interactions.
Nakazawa (2013) explored suites of factors that could explain the present-day biodiversity pattern across South America. This study supported climate, seasonal variability, and river barriers as jointly required to approximate present-day patterns. Nakazawa and Peterson (2015) added a further dimension to these questions: global-scale climate changes over the end of the Pleistocene, from the warm Last Interglacial period, through the cool Last Glacial Maximum, to the warm present-day conditions. Based on simple assumptions about dispersal potential and persistence of species, they developed a subtractive view (i.e., if species existed at a place, would they survive the last glacial cycle of the Pleistocene?) of biodiversity patterns across South America and Africa. That is, stability in environments in Africa in this period was markedly lower than that in South America. These differences created marked contrasts between the two continents in simulated extinction rates that approximate real-world differences in forest biodiversity.
This suite of explorations by various researchers has suggested a set of ‘next steps’: a simulation environment that permits assessment of the number of processes necessary to explain the major features of global biodiversity pattern. A general simulation model similar to that envisioned by Gotelli et al. (2009) has been developed and implemented across Eurasia, to assess the relative roles of niche breadth, dispersal, and rates of environmental change, in driving speciation and extinction (Qiao et al. 2016). This model is now being extended to include more realistic climate dynamics, and landscapes and environments worldwide. The goal is to assess the degree to which global biodiversity patterns are explained without the need to appeal to biotic interactions—for example, what is the balance of historical versus current ecological factors in driving diversity patterns? The answers to such questions must await considerable additional exploration and testing, but, positively, frameworks to answer them with appropriate spatiotemporal scales and extents are now being explored.
Gaston, K. J. 2000. Global patterns in biodiversity. Nature 405: 220-227.
Gotelli, N. J., M. J. Anderson, H. T. Arita, A. Chao, R. K. Colwell, S. R. Connolly, D. J. Currie, R. R. Dunn, G. R. Graves, J. L. Green, J. Arvid, Y.-H. J. Grytnes, W. Jetz, S. K. Lyons, C. M. McCain, A. E. Magurran, C. Rahbek, T. F. L. V. B. Rangel, J. Soberón, C. O. Webb, and M. R. Willig. 2009. Patterns and causes of species richness: A general simulation model for macroecology. Ecology Letters 12: 873-886.
Kleidon, A., J. Adams, R. Pavlick, and B. Reu. 2009. Simulated geographic variations of plant species richness, evenness and abundance using climatic constraints on plant functional diversity. Environmental Research Letters 4: 014007.
Nakazawa, Y. 2013. Niche breadth, environmental landscape, and physical barriers: Their importance as determinants of species distributions. Biological Journal of the Linnean Society 108: 241-250.
Nakazawa, Y., and A. T. Peterson. 2015. Effects of climate history and environmental grain on species’ distributions in Africa and South America. Biotropica 47: 292-299.
Orme, C. D. L., R. G. Davies, V. A. Olson, G. H. Thomas, T.-S. Ding, P. C. Rasmussen, R. S. Ridgely, A. J. Stattersfield, P. M. Bennett, and I. P. Owens. 2006. Global patterns of geographic range size in birds. PLoS Biology 4: e208.
Qiao, H., E. E. Saupe, J. Soberón, A. T. Peterson, C. E. Myers, D. C. Collar, and J. L. Bronstein. 2016. Impacts of niche breadth and dispersal ability on macroevolutionary patterns. American Naturalist 188.
Rangel, T. F. L. V. B., J. A. F. Diniz-Filho, and R. K. Colwell. 2007. Species richness and evolutionary niche dynamics: A spatial pattern-oriented simulation experiment. American Naturalist 170: 602-616.
Reu, B., R. Proulx, K. Bohn, J. G. Dyke, A. Kleidon, R. Pavlick, and S. Schmidtlein. 2011. The role of climate and plant functional trade‐offs in shaping global biome and biodiversity patterns. Global Ecology and Biogeography 20: 570-581.
Ricklefs, R. E. 2004. A comprehensive framework for global patterns in biodiversity. Ecology Letters 7: 1-15.
Storch, D., R. G. Davies, S. Zajíček, C. D. L. Orme, V. Olson, G. H. Thomas, T. S. Ding, P. C. Rasmussen, R. S. Ridgely, and P. M. Bennett. 2006. Energy, range dynamics and global species richness patterns: Reconciling mid‐domain effects and environmental determinants of avian diversity. Ecology Letters 9: 1308-1320.
Willig, M. R., D. M. Kaufman, and R. D. Stevens. 2003. Latitudinal gradients of biodiversity: Pattern, process, scale, and synthesis. Annual Review of Ecology, Evolution, and Systematics 34: 273-309.
2016 Peter Ashton Prize
For the Outstanding Paper in Biotropica by a Student
Franziska Peter, Dana G. Berens, Graham R. Grieve and Nina Farwig. 2015). Forest Fragmentation Drives the Loss of Insectivorous Birds and an Associated Increase in Herbivory. Biotropica, 47: 626–635.
Insectivorous birds are known to play a decisive role for the natural control of herbivorous insects. Thus, they enhance the growth, reproduction, and survival of plant individuals and in the long-term benefit plant regeneration. However, particularly in the tropics, forest fragmentation has been suggested to cause a loss of insectivorous birds. Yet, it is unclear whether this hampers the trophic control of herbivorous insects with potential consequences for plants. Therefore, we investigated the effect of increasing forest fragmentation on tritrophic interactions between insectivorous birds, herbivorous insects, and plants in a subtropical forest landscape, South Africa. We monitored the community composition of birds and estimated insectivorous bird abundances along a gradient of forest fragmentation. In the same sites, we installed bird exclosures on a common plant species (Englerophytum natalense) to assess effects of the trophic control of insectivorous birds on herbivorous insects and leaf area loss (LAL). Forest fragmentation strongly shaped the functional composition of bird communities, particularly through a loss of forest-dependent insectivorous birds. Moreover, LAL was higher within bird exclosures than on control branches and increased with increasing forest fragmentation on the control branches. Altogether, forest fragmentation seems to hamper the trophic control of herbivorous insects by insectivorous birds through changes in the community composition. This, in turn, may interfere with tritrophic interactions and ecological processes. Thus, conservation efforts aiming at enhancing the natural control of herbivorous insects should focus on the maintenance of continuous indigenous forests that are well-connected to smaller forest fragments on the landscape scale.
Does Forest Fragmentation Trigger Ecological Cascades?
My first experience with comprehensive ecological field studies was during my diploma thesis. Under the supervision of Prof. Dr. Tim Diekötter and Dr. Frank Jauker I studied the effects of oilseed rape and semi-natural habitats on pollinator communities and related ecosystem services in a temperate agricultural landscape matrix. Findings were highly complex as pollinator responses were species-specific (with respect to social and nesting behaviour as well as morphological traits) and showed temporal and spatial variability. Furthermore, I became aware of the strong and multifaceted consequences of human-driven land-use changes – ranging from the sheer loss of species and shifts in the composition of pollinator communities to cruel things such as “nectar robbing” as well as reduced reproductive success of wild bees and associated wild plants.
Following my diploma thesis I was excited when Prof. Dr. Nina Farwig welcomed me in her working group. With the PhD position I was given the opportunity to complement my knowledge on effects of human-driven land-use changes on trophic interactions by adding antagonistic plant-herbivore and predator-prey interactions in diverse and structurally complex subtropical forest ecosystems. Being part of a keen research team (supported by the Robert Bosch Stiftung) focussing on the impact of numerous anthropogenic drivers on biotic communities and related ecological processes and ecosystem functioning I could not await the following years. My excitement grew when I first visited South Africa and the previously established study region located at the Oribi Gorge Nature Reserve in southern KwaZulu-Natal. I was astonished by the overwhelming diversity of animal and plant species. Having no experience with subtropical ecosystems it took me a few weeks to be able to identify the majority of tree species within unmanaged rather indigenous forests. However, particularly the fascination about the infinite biodiversity drove me to improve species knowledge, grow expertise for complex trophic interactions in highly diverse forests and fuelled my enthusiasm for field work. As a result, field work, broadening my knowledge in landscape and conservation ecology, daily encounters with wildlife, being integrated in a highly motivated research group as well as the local South African community created an unforgettable experience.
I did two subsequent field studies and the nomination of the latter study for Biotropica‘s Ashton Prize is of great honor to me and my co-authors. The first study focussed on main and interactive effects of forest fragmentation and tree diversity on plant-herbivore interactions. In brief, findings of this study revealed that effects of local tree diversity on plant-herbivore interactions diminished with increasing forest fragmentation on the landscape scale. With the second study I aimed to build on previous research that investigated effects of habitat fragmentation on either plant-herbivore or predator-prey interactions. In particular, I was curious whether forest fragmentation triggers cascades across multitrophic interactions and changes patterns in ecosystem functioning. Hence, I simultaneously monitored bird communities, insect herbivore abundances as well as leaf area loss along an increasing degree of forest fragmentation. I quantified the trophic control of herbivorous insects by insectivorous birds through bird exclosures attached to the common tree species Englerophytum natalensis. Installing the bird exclosure and the control at the same plant individual enabled me to exclude confounding effects of the microhabitat and the individual plant history and thus, to focus on the impact of forest fragmentation on plant-herbivore interactions through changes in the local bird community. Findings offered insights into complex effects of forest fragmentation on multitrophic interactions. Both forest fragmentation and vegetation heterogeneity structured the functional composition of bird communities as a result of species-specific forest-dependency and resource requirements as well as preferences for structural forest habitat features. As a consequence, open-habitat omnivorous birds seemed to benefit from forest fragmentation while abundances of forest-dependent insectivorous birds decreased with increasing forest fragmentation. However, I found no significant difference in the abundance of herbivorous insects within the bird exclosure relative to the control which may be explained by the restriction to a rather seasonal “snapshot” of the insect herbivore community. In fact, leaf area loss which accumulated during the study period was higher when birds were excluded supporting the functional role of insectivorous birds for the natural control of herbivorous insects. Finally, the increase of leaf area loss for the control branches with increasing forest fragmentation implies that increasing forest fragmentation diminished the natural control of herbivorous insects by insectivorous birds.
Overall, findings of my study show that forest fragmentation in fact seems to trigger cascades across multitrophic interactions and ultimately, may hamper ecosystem functioning. Therefore, the application of multitrophic approaches offers new insights into the comprehensive impact of anthropogenic drivers and enables to discover changes in ecological processes and thus, ecosystem functioning. In addition, results support previous studies that concluded that the protection and connectivity of preferably large forest habitats benefits ecosystem functioning.
Peter et al. 2015 was a chapter in Dr. Peter’s doctoral dissertation, completed at the Faculty of Biology, Philipps-Universität Marburg (Marburg, Germany).