Julian Resasco

Potential Negative Ecological Effects of Corridors

Despite many studies showing that landscape corridors increase dispersal and species richness for disparate taxa, concerns persist that corridors can have unintended negative effects. In particular, some of the same mechanisms that underlie positive effects of corridors on species of conservation interest may also increase the spread and impact of antagonistic species (e.g., predators and pathogens), foster negative effects of edges, increase invasion by exotic species, increase the spread of unwanted disturbances such as fire, or increase population synchrony and thus reduce persistence. We conducted a literature review and meta-analysis to evaluate the prevalence of each of these negative effects. We found no evidence that corridors increase unwanted disturbance or non-native species invasion; however, these have not been well-studied concerns (1 and 6 studies, respectively). Other effects of corridors were more often studied and yielded inconsistent results; mean effect sizes were indistinguishable from zero. The effect of edges on abundances of target species was as likely to be positive as negative. Corridors were as likely to have no effect on antagonists or population synchrony as they were to increase those negative effects. We found 3 deficiencies in the literature. First, despite studies on how corridors affect predators, there are few studies of related consequences for prey population size and persistence. Second, properly designed studies of negative corridor effects are needed in natural corridors at scales larger than those achievable in experimental systems. Third, studies are needed to test more targeted hypotheses about when corridor-mediated effects on invasive species or disturbance may be negative for species of management concern. Overall, we found no overarching support for concerns that construction and maintenance of habitat corridors may result in unintended negative consequences. Negative edge effects may be mitigated by widening corridors or softening edges between corridors and the matrix. Other negative effects are relatively small and manageable compared with the large positive effects of facilitating dispersal and increasing diversity of native species.

Improving Wikipedia: educational opportunity and professional responsibility.

The rise of user-generated Internet content (i.e. ‘Web 2.0’) has resulted in dramatic changes in the way that scientific information is collected and disseminated. One notable example is Wikipedia (http://www.wikipedia.org), the user-written online encyclopedia with millions of users worldwide. In the 7 years since its inception it has become a staple of the academic community, increasingly used by faculty and students to develop lectures and study aids, research topics for papers and as a source of background information while studying or conducting research.

Evaluating conceptual models of landscape change

&NA; A variety of landscape models are used to conceptualize and interpret human impacts on ecosystems and their biodiversity. The simplest, a ‘patch‐matrix’ model, is rooted in island biogeography theory and assumes a dichotomy between generic, easily‐defined habitat patches and a surrounding matrix that is completely inhospitable. This dichotomy between patch and matrix habitats has been recently relaxed, with the ‘continuum’ model taking this relaxation to its extreme and logical endpoint – a species‐based model with no a priori definition of habitat or matrix, but rather focusing on ecological gradients. Yet, because few empirical comparisons of these bookending models exist, we lack understanding of their relative utility or the merits of hybrid approaches that combine attributes of patch‐matrix and continuum models. To guide such considerations, we first develop a decision‐making framework for the application of patch‐matrix, continuum, and hybrid models. The framework takes into account study objectives, attributes of the landscape, and species traits. We then evaluate this framework by empirically comparing how continuum, patch‐matrix, and hybrid models explain beetle distributions across two contrasting fragmented landscapes, for species differing in trophic level and habitat specificity. Within the Hope River Forest Fragmentation Project, a system with strong landscape contrast and distinct (‘hard’) structural edges between forest fragments and grassland, we find broad support for hybrid models, particularly those incorporating surrounding landscape structure. Conversely, within the Wog Wog Habitat Fragmentation Experiment, a system with weak landscape contrast and ‘soft’ structural edges between natural and plantation forest, we find co‐support for continuum and hybrid models. We find no support in either system for patch‐matrix, relative to continuum and hybrid models. We conclude by considering key questions and areas of research for advancing the application of models to understand species responses and biodiversity patterns associated with land‐use change.

Using Historical and Experimental Data to Reveal Warming Effects on Ant Assemblages

Historical records of species are compared with current records to elucidate effects of recent climate change. However, confounding variables such as succession, land-use change, and species invasions make it difficult to demonstrate a causal link between changes in biota and changes in climate. Experiments that manipulate temperature can overcome this issue of attribution, but long-term impacts of warming are difficult to test directly. Here we combine historical and experimental data to explore effects of warming on ant assemblages in southeastern US. Observational data span a 35-year period (1976–2011), during which mean annual temperatures had an increasing trend. Mean summer temperatures in 2010–2011 were ∼2.7°C warmer than in 1976. Experimental data come from an ongoing study in the same region, for which temperatures have been increased ∼1.5–5.5°C above ambient from 2010 to 2012. Ant species richness and evenness decreased with warming under natural but not experimental warming. These discrepancies could have resulted from differences in timescales of warming, abiotic or biotic factors, or initial species pools. Species turnover tended to increase with temperature in observational and experimental datasets. At the species level, the observational and experimental datasets had four species in common, two of which exhibited consistent patterns between datasets. With natural and experimental warming, collections of the numerically dominant, thermophilic species, Crematogaster lineolata, increased roughly two-fold. Myrmecina americana, a relatively heat intolerant species, decreased with temperature in natural and experimental warming. In contrast, species in the Solenopsis molesta group did not show consistent responses to warming, and Temenothorax pergandei was rare across temperatures. Our results highlight the difficulty of interpreting community responses to warming based on historical records or experiments alone. Because some species showed consistent responses to warming based on thermal tolerances, understanding functional traits may prove useful in explaining responses of species to warming.

A global database of ant species abundances

What forces structure ecological assemblages? A key limitation to general insights about assemblage structure is the availability of data that are collected at a small spatial grain (local assemblages) and a large spatial extent (global coverage). Here, we present published and unpublished data from 51 ,388 ant abundance and occurrence records of more than 2,693 species and 7,953 morphospecies from local assemblages collected at 4,212 locations around the world. Ants were selected because they are diverse and abundant globally, comprise a large fraction of animal biomass in most terrestrial communities, and are key contributors to a range of ecosystem functions. Data were collected between 1949 and 2014, and include, for each geo-referenced sampling site, both the identity of the ants collected and details of sampling design, habitat type, and degree of disturbance. The aim of compiling this data set was to provide comprehensive species abundance data in order to test relationships between assemblage structure and environmental and biogeographic factors. Data were collected using a variety of standardized methods, such as pitfall and Winkler traps, and will be valuable for studies investigating large-scale forces structuring local assemblages. Understanding such relationships is particularly critical under current rates of global change. We encourage authors holding additional data on systematically collected ant assemblages, especially those in dry and cold, and remote areas, to contact us and contribute their data to this growing data set.

Assessing the effects of sodium on fire ant foraging in the field and colony growth in the laboratory

Sodium is an essential dietary element and preferential foraging for high concentrations of sodium by inland herbivorous and omnivorous ants suggests it may be limiting. If so, increased sodium availability through altered deposition and anthropogenic sources may lead to increased colony and population growth and cascading ecological impacts. For red imported fire ants, Solenopsis invicta Buren, the present study tests: (i) whether colonies from coastal and inland sites differ in their responses to NaCl baits; and (ii) whether supplemental NaCl increases growth of fire ant colonies in the laboratory. Fire ants in inland sites with low sodium deposition responded roughly an order of magnitude more strongly to high concentrations of NaCl baits than did fire ants in coastal sites with high sodium deposition. Laboratory colonies of fire ants, however, showed no signs of sodium limitation or benefits of increased sodium. The link between behavioural responses to baits in the field and effects on colony growth deserves further investigation to assess the ecological impacts of altered sodium availability.

Interaction frequency, network position, and the temporal persistence of interactions in a plant–pollinator network

Ecological interactions are highly dynamic in time and space. Previous studies of plant-animal mutualistic networks have shown that the occurrence of interactions varies substantially across years. We analyzed interannual variation of a quantitative mutualistic network, in which links are weighted by interaction frequency. The network was sampled over six consecutive years, representing one of the longest time series for a community-wide mutualistic network. We estimated the interannual similarity in interactions and assessed the determinants of their persistence. The occurrence of interactions varied greatly among years, with most interactions seen in only one year (64%) and few (20%) in more than two years. This variation was associated with the frequency and position of interactions relative to the network core, so that the network consisted of a persistent core of frequent interactions and many peripheral, infrequent interactions. Null model analyses suggest that species abundances play a substantial role in generating these patterns. Our study represents an important step in the study of ecological networks, furthering our mechanistic understanding of the ecological processes driving the temporal persistence of interactions.

Invasive Ants Generate Heterogeneity in Patterns of Seed Survival

Abstract Although studies often focus on the direct effects of invasive species on native taxa, invasive species may also alter interactions among native species. For example Solenopsis invicta, the red imported fire ant, may directly alter native seed survival by consuming seeds, but also indirectly alter seed survival, by altering the abundance and/or behavior of native granivores. We tested the effects of invasive S. invicta on rodent and arthropod granivory by quantifying seed removal from seed depots that differed in granivore access (arthropods and rodents or arthropods only) and distance from an S. invicta mound (0.1 m or 4.0 m). We hypothesized the effect of S. invicta on native granivores would be stronger at depots located near (0.1 m) a mound than at depots located 4.0 m from a mound. Use of two different seed species (Rubus cuneifolius and Prunus serotina) allowed us to evaluate the consequences of S. invicta for small-seeded plant species consumed by both arthropods and rodents (R. cuneifolius) as well as for large-seeded species that can only be consumed by rodents (P. serotina). We found overall removal of P. serotina was low, regardless of seed depot location or exclosure type. Near S. invicta mounds, the removal of R. cuneifolius was also low, with no difference between depots that allowed or excluded rodents. In contrast, removal of R. cuneifolius by arthropods 4.0 m from a mound was nearly twice that of removal next to a mound but only when rodents were excluded. Our results indicate S. invicta may create hotspots of granivory by native arthropods in the areas between S. invicta mounds, but these effects may not extend to large-seeded plants that are consumed by rodents. By influencing seed survival as a function of plant species and proximity to a mound, nonnative S. invicta generates heterogeneity in native seed survival, which may affect plant community composition.

Generalist predator's niche shifts reveal ecosystem changes in an experimentally fragmented landscape

Habitat fragmentation can alter the trophic structure of communities and environmental conditions, thus driving changes in biodiversity and ecosystem functions. Quantifying niches of generalist predators can reveal how fragmentation alters ecosystems. In a habitat fragmentation experiment, we used stable isotopes of a generalist predator skink to test predictions from spatial theory on trophic structure and to quantify abiotic changes associated with fragmentation among continuous forest, fragments, and matrix habitats. We predicted that in fragments and the matrix, isotopic niches would shift due to decreases in skink trophic positions (δ15N) from reductions in trophic structure of arthropod food webs and abiotic changes over time (δ13C) relative to continuous forest. Contrary to theoretical predictions, we did not find evidence of reductions in trophic structure with fragmentation. In fact, skink δ15N values were higher in the matrix and fragments than continuous forest, likely due to changes in distributions of a detritivorous prey species. In addition, δ13C values in the matrix decreased over years since fragmentation due to abiotic changes associated with matrix tree maturation. We show how isotopic niches are influenced by fragmentation via shifts in biotic and abiotic processes. The potential for either or both spatial and abiotic effects of fragmentation present a challenge for theory to better predict ecological changes in fragmented landscapes.