Linking richness, community variability, and invasion resistance with patch size

The influence of community dynamics on the success or failure of an invasion is of considerable interest. What has not been explored is the influence of patch size on the outcomes of invasions for communities with the same species pool. Here we use an empirically validated spatial model of a marine epibenthic community to examine the effects of patch size on community variability, species richness, invasion, and the relationships between these variables. We found that the qualitative form of the relationship between community variability and species richness is determined by the size of the model patch. In small patches, variability decreases with species richness, but beyond a critical patch size, variability increases with increasing richness. This occurs because in large patches large, long-lived colonies attain sufficient size to minimize mortality and dominate the community, leading to decreased species richness and community variability. This mechanism cannot operate on smaller patches where the size of colonies is limited by the patch size and mortality is high irrespective of species identity. Further, invasion resistance is strongly correlated with community variability. Thus, the relationship between species richness and invasion resistance is also determined by patch size. These patterns are generated largely by an inverse relationship between colony size and mortality, and they depend on the spatial nature and patch size of the community. Our results suggest that a continuum of possible relationships can exist between species richness, community variability, invasion resistance, and area. These relationships are emergent behaviors generated by the individual properties of the particular component species of a community.     

Feasibility study of using brine for carbon dioxide capture and storage from fixed sources

A laboratory-scale reactor was developed to evaluate the capture of carbon dioxide (CO2) from a gas into a liquid as an approach to control greenhouse gases emitted from fixed sources. CO2 at 5-50% concentrations was passed through a gas-exchange membrane and transferred into liquid media--tap water or simulated brine. When using water, capture efficiencies exceeded 50% and could be enhanced by adding base (e.g., sodium hydroxide) or the combination of base and carbonic anhydrase, a catalyst that speeds the conversion of CO2 to carbonic acid. The transferred CO2 formed ions, such as bicarbonate or carbonate, depending on the amount of base present. Adding precipitating cations, like Ca++, produced insoluble carbonate salts. Simulated brine proved nearly as efficient as water in absorbing CO2, with less than a 6% reduction in CO2 transferred. The CO2 either dissolved into the brine or formed a mixture of gas and ions. If the chemistry was favorable, carbonate precipitate spontaneously formed. Energy expenditure of pumping brine up and down from subterranean depths was modeled. We conclude that using brine in a gas-exchange membrane system for capturing CO2 from a gas stream to liquid is technically feasible and can be accomplished at a reasonable expenditure of energy.     

Parasite competition hidden by correlated coinfection: using surveys and experiments to understand parasite interactions

Within most free-living species exists a cryptic community of interacting parasites. By combining multiscale field data with manipulative experiments, we evaluated patterns of parasite coinfection in amphibian hosts and their underlying mechanisms. Surveys of 86 wetlands and 1273 hosts revealed positive correlations between two pathogenic trematodes (Ribeiroia ondatrae and Echinostoma trivolvis) both between wetlands and within individual hosts. In infection and coinfection experiments, Ribeiroia caused greater pathology than Echinostoma, including high host mortality (24%) and severe limb malformations (75%). No interactive effects were noted for host pathology, but both parasites decreased the per capita persistence of one another by 17-36%. Thus, in spite of consistently positive associations from field data, these parasites negatively affected the persistence of one another, likely via cross immunity (apparent competition). These findings underscore the danger of inferring parasite interactions from coinfection patterns and emphasize the potential disconnect between within-host processes (e.g., competition) and between-host processes (e.g., exposure and transmission). Here, correlated coinfections likely resulted from similarities in the parasites' host requirements and heterogeneity in host susceptibility or exposure. Understanding complex interactions among parasites depends critically on the scale under consideration, highlighting the importance of combining coinfection field studies with mechanistic experiments.     

Association of body mass with price of bushmeat in Nigeria and Cameroon

Spatially extensive patterns of bushmeat extraction (and the processes underlying these patterns) have not been explored. We used data from a large sample (n= 87) of bushmeat trading points in urban and rural localities in Nigeria and Cameroon to explore extraction patterns at a regional level. In 7,594 sample days, we observed 61,267 transactions involving whole carcasses. Rural and urban trading points differed in species for sale and in meat condition (fresh or smoked). Carcass price was principally associated with body mass, with little evidence that taxonomic group (primate, rodent, ungulate, or mammalian carnivore) affected price. Moreover, meat condition was not consistently associated with price. However, some individual species were more expensive throughout the region than would be expected for their size. Prices were weakly positively correlated with human settlement size and were highest in urban areas. Supply did not increase proportionally as human settlement size increased, such that per capita supply was significantly lower in urban centers than in rural areas. Policy options, including banning hunting of more vulnerable species (those that have low reproductive rates), may help to conserve some species consumed as bushmeat because carcass prices indicate that faster breeding, and therefore the more sustainable species, may be substituted and readily accepted by consumers.     

Monitoring seasonal bat activity on a coastal barrier island in Maryland, USA

Research on effects of wind turbines on bats has increased dramatically in recent years because of significant numbers of bats killed by rotating wind turbine blades. Whereas most research has focused on the Midwest and inland portions of eastern North America, bat activity and migration on the Atlantic Coast has largely been unexamined. We used three long-term acoustic monitoring stations to determine seasonal bat activity patterns on the Assateague Island National Seashore, a barrier island off the coast of Maryland, from 2005 to 2006. We recorded five species, including eastern red bats (Lasiurus borealis), big brown bats (Eptesicus fuscus), hoary bats (Lasiurus cinereus), tri-colored bats (Perimyotis subflavus), and silver-haired bats (Lasionycteris noctivagans). Seasonal bat activity (number of bat passes recorded) followed a cosine function and gradually increased beginning in April, peaked in August, and declined gradually until cessation in December. Based on autoregressive models, inter-night bat activity was autocorrelated for lags of seven nights or fewer but varied among acoustic monitoring stations. Higher nightly temperatures and lower wind speeds positively affected bat activity. When autoregressive model predictions were fitted to the observed nightly bat pass totals, model residuals >2 standard deviations from the mean existed only during migration periods, indicating that periodic increases in bat activity could not be accounted for by seasonal trends and weather variables alone. Rather, the additional bat passes were attributable to migrating bats. We conclude that bats, specifically eastern red, hoary, and silver-haired bats, use this barrier island during migration and that this phenomenon may have implications for the development of near and offshore wind energy.     

Hazards from carbon dioxide capture, transport and storage

Carbon capture and storage (CCS) is a developing technology which raises a number of issues in terms of safety. CCS involves a chain of processes comprising capture of carbon dioxide, transport and injection into underground storage. In work carried out for the IEA Greenhouse Gas R&D Programme, a number of high-level hazard identification (HAZID) studies have been performed with the help of industry experts. The HAZIDs considered a carbon capture and storage chain involving capture, pipeline transport and injection. HAZID has been performed at a high-level for such a CCS chain with three types of capture technology and using pipeline transport. It is hoped that the results of the HAZID studies will be of use to those carrying out CCS projects, but should not be a substitute for them carrying out a full suite of integrated hazard management processes. A number of example hazards have been described to raise awareness of the range of hazards in a CCS process and to identify barriers which could prevent, minimise, control or mitigate CCS hazards. Bow-tie diagrams have been produced to record the information from this study and to organise it in a systematic way so that it is far less likely that contributors to and mitigators of hazards will be missed. The diagrams are available in Excel spreadsheet format so that they can be used as the starting point for development by specific CCS projects. CCS technology is still advancing and a number of knowledge gaps in terms of safety have been identified which require further development.     

Alternative stable states and phase shifts in coral reefs under anthropogenic stress

Ecosystems with alternative stable states (ASS) may shift discontinuously from one stable state to another as environmental parameters cross a threshold. Reversal can then be difficult due to hysteresis effects. This contrasts with continuous state changes in response to changing environmental parameters, which are less difficult to reverse. Worldwide degradation of coral reefs, involving "phase shifts" from coral to algal dominance, highlights the pressing need to determine the likelihood of discontinuous phase shifts in coral reefs, in contrast to continuous shifts with no ASS. However, there is little evidence either for or against the existence of ASS for coral reefs. We use dynamic models to investigate the likelihood of continuous and discontinuous phase shifts in coral reefs subject to sustained environmental perturbation by fishing, nutrification, and sedimentation. Our modeling results suggest that coral reefs with or without anthropogenic stress can exhibit ASS, such that discontinuous phase shifts can occur. We also find evidence to support the view that high macroalgal growth rates and low grazing rates on macroalgae favor ASS in coral reefs. Further, our results suggest that the three stressors studied, either alone or in combination, can increase the likelihood of both continuous and discontinuous phase shifts by altering the competitive balance between corals and algae. However, in contrast to continuous phase shifts, we find that discontinuous shifts occur only in model coral reefs with parameter values near the extremes of their empirically determined ranges. This suggests that continuous shifts are more likely than discontinuous shifts in coral reefs. Our results also suggest that, for ecosystems in general, tackling multiple human stressors simultaneously maximizes resilience to phase shifts, ASS, and hysteresis, leading to improvements in ecosystem health and functioning.     

Disentangling the drivers of reduced long-distance seed dispersal by birds in an experimentally fragmented landscape

Seed dispersal is a crucial component of plant population dynamics. Human landscape modifications, such as habitat destruction and fragmentation, can alter the abundance of fruiting plants and animal dispersers, foraging rates, vector movement, and the composition of the disperser community, all of which can singly or in concert affect seed dispersal. Here, we quantify and tease apart the effects of landscape configuration, namely, fragmentation of primary forest and the composition of the surrounding forest matrix, on individual components of seed dispersal of Heliconia acuminata, an Amazonian understory herb. First we identified the effects of landscape configuration on the abundance of fruiting plants and six bird disperser species. Although highly variable in space and time, densities of fruiting plants were similar in continuous forest and fragments. However, the two largest-bodied avian dispersers were less common or absent in small fragments. Second, we determined whether fragmentation affected foraging rates. Fruit removal rates were similar and very high across the landscape, suggesting that Heliconia fruits are a key resource for small frugivores in this landscape. Third, we used radiotelemetry and statistical models to quantify how landscape configuration influences vector movement patterns. Bird dispersers flew farther and faster, and perched longer in primary relative to secondary forests. One species also altered its movement direction in response to habitat boundaries between primary and secondary forests. Finally, we parameterized a simulation model linking data on fruit density and disperser abundance and behavior with empirical estimates of seed retention times to generate seed dispersal patterns in two hypothetical landscapes. Despite clear changes in bird movement in response to landscape configuration, our simulations demonstrate that these differences had negligible effects on dispersal distances. However, small fragments had reduced densities of Turdus albicollis, the largest-bodied disperser and the only one to both regurgitate and defecate seeds. This change in Turdus abundance acted together with lower numbers of fruiting plants in small fragments to decrease the probability of long-distance dispersal events from small patches. These findings emphasize the importance of foraging style for seed dispersal and highlight the primacy of habitat size relative to spatial configuration in preserving biotic interactions.     

Nestmate recognition in social insects: overcoming physiological constraints with collective decision making

Social insects rank among the most abundant and influential terrestrial organisms. The key to their success is their ability to form tightly knit social groups that perform work cooperatively, and effectively exclude non-members from the colony. An extensive body of research, both empirical and theoretical, has explored how optimal acceptance thresholds could evolve in individuals, driven by the twin costs of inappropriately rejecting true nestmates and erroneously accepting individuals from foreign colonies. Here, in contrast, we use agent-based modeling to show that strong nestmate recognition by individuals is often unnecessary. Instead, highly effective nestmate recognition can arise as a colony-level property from a collective of individually poor recognizers. Essentially, although an intruder can get by one defender when their odor cues are similar, it is nearly impossible to get past many defenders if there is the slightest difference in cues. The results of our models match observed rejection rates in studies of ants, wasps, and bees. We also show that previous research in support of the optimal threshold theory approach to the problem of nestmate recognition can be alternatively viewed as evidence in favor of the collective formation of a selectively permeable barrier that allows in nestmates (at a significant cost) while rejecting non-nestmates. Finally, this work shows that nestmate recognition has a stronger task allocation component than previously thought, as colonies can nearly always achieve perfect nestmate recognition if it is cost effective for them to do so at the colony level.