Ensemble ecosystem modeling for predicting ecosystem response to predator reintroduction

Introducing a new or extirpated species to an ecosystem is risky, and managers need quantitative methods that can predict the consequences for the recipient ecosystem. Proponents of keystone predator reintroductions commonly argue that the presence of the predator will restore ecosystem function, but this has not always been the case, and mathematical modeling has an important role to play in predicting how reintroductions will likely play out. We devised an ensemble modeling method that integrates species interaction networks and dynamic community simulations and used it to describe the range of plausible consequences of 2 keystone‐predator reintroductions: wolves (Canis lupus) to Yellowstone National Park and dingoes (Canis dingo) to a national park in Australia. Although previous methods for predicting ecosystem responses to such interventions focused on predicting changes around a given equilibrium, we used Lotka–Volterra equations to predict changing abundances through time. We applied our method to interaction networks for wolves in Yellowstone National Park and for dingoes in Australia. Our model replicated the observed dynamics in Yellowstone National Park and produced a larger range of potential outcomes for the dingo network. However, we also found that changes in small vertebrates or invertebrates gave a good indication about the potential future state of the system. Our method allowed us to predict when the systems were far from equilibrium. Our results showed that the method can also be used to predict which species may increase or decrease following a reintroduction and can identify species that are important to monitor (i.e., species whose changes in abundance give extra insight into broad changes in the system). Ensemble ecosystem modeling can also be applied to assess the ecosystem‐wide implications of other types of interventions including assisted migration, biocontrol, and invasive species eradication.     

Accounting for adaptive capacity and uncertainty in assessments of species’ climate‐change vulnerability

Climate‐change vulnerability assessments (CCVAs) are valuable tools for assessing species’ vulnerability to climatic changes, yet failure to include measures of adaptive capacity and to account for sources of uncertainty may limit their effectiveness. We took a more comprehensive approach that incorporates exposure, sensitivity, and capacity to adapt to climate change. We applied our approach to anadromous steelhead trout (Oncorhynchus mykiss) and nonanadromous bull trout (Salvelinus confluentus), threatened salmonids within the Columbia River Basin (U.S.A.). We quantified exposure on the basis of scenarios of future stream temperature and flow, and we represented sensitivity and capacity to adapt to climate change with metrics of habitat quality, demographic condition, and genetic diversity. Both species were found to be highly vulnerable to climate change at low elevations and in their southernmost habitats. However, vulnerability rankings varied widely depending on the factors (climate, habitat, demographic, and genetic) included in the CCVA and often differed for the 2 species at locations where they were sympatric. Our findings illustrate that CCVA results are highly sensitive to data inputs and that spatial differences can complicate multispecies conservation. Based on our results, we suggest that CCVAs be considered within a broader conceptual and computational framework and be used to refine hypotheses, guide research, and compare plausible scenarios of species’ vulnerability to climate change.     

Application of environmental DNA analysis to inform invasive fish eradication operations

Environmental DNA (eDNA) detection of non-native species has considerable potential to inform management decisions, including identifying the need for population control and/or eradication. An invasive species of European concern is the Asian cyprinid fish, topmouth gudgeon (Pseudorasbora parva). Here, eDNA analyses were applied at a commercial angling venue in southern England to inform operations aiming to eradicate P. parva, which had only ever been observed in one of the venue’s seven unconnected angling ponds. Eradication of P. parva was initially attempted by repeated depletion of the population using fish traps (crayfish traps fitted with 5 mm mesh netting) and the introduction of native predators over a 4-year period. The very low number of P. parva captured following these eradication efforts suggested a possible population crash. Conventional PCR analysis of water samples using species-specific primers was applied to all seven ponds to confirm that P. parva was present in only one pond, that the eradication attempt had indeed failed and that the species’ distribution in the pond appeared to be restricted to three bankside locations. The continued presence of P. parva at these locations was confirmed by subsequent trapping. Water samples from an adjacent, unconnected stream were also analysed using the eDNA methodology, but no DNA of P. parva was detected. The results suggest that further management action to eradicate P. parva be focused on the pond shown to contain the isolated P. parva population and thereby eliminate the risk of further dispersal. This study is the first to apply eDNA analysis to assess the efficacy of an eradication attempt and to provide evidence that the species was unlikely to be present in the other ponds, thus reducing the resources needed to control the species.     

Pastoralists' responses to variation of rangeland resources in time and space.

We explore the response of pastoralists to rangeland resource variation in time and space, focusing on regions where high variation makes it unlikely that an economically viable herd can be maintained on a single management unit. In such regions, the need to move stock to find forage in at least some years has led to the evolution of nomadism and transhumance, and reciprocal grazing agreements among the holders of common-property rangeland. The role of such informal institutions in buffering resource variation is well documented in some Asian and African rangelands, but in societies with formally established private-property regimes, where we focus, such institutions have received little attention. We examine agistment networks, which play an important role in buffering resource variation in modern-day Australia. Agistment is a commercial arrangement between pastoralists who have less forage than they believe they require and pastoralists who believe they have more. Agistment facilitates the movement of livestock via a network based largely on trust. We are concerned exclusively with the link between the characteristics of biophysical variation and human aspects of agistment networks, and we developed a model to test the hypothesis that such a link could exist. Our model builds on game theory literature, which explains cooperation between strangers based on the ability of players to learn whom they can trust. Our game is played on a highly stylized landscape that allows us to control and isolate the degree of spatial variation and spatial covariation. We found that agistment networks are more effective where spatial variation in resource availability is high, and generally more effective when spatial covariation is low. Policy design that seeks to work with existing social networks in rangelands has potential, but this potential varies depending on localized characteristics of the biophysical variability.     

Deep-sea bottom-living fishes at two repeat stations at 2 200 and 2 900 m in the Rockall Trough,northeastern Atlantic Ocean

Repeated sampling of deep-sea bottom-living fishes was conducted at two stations in the Rockall Trough at depths of 2 200 and 2 900 m. The 2 200 m station (M) was sampled 16 times by an Agassiz trawl between April 1978 and April 1985 and yielded 473 fish belonging to 17 species. The 2 900 m permanent station (PS) yielded 781 fish belonging to 11 species from 9 Agassiz trawls, 2 small box otter trawls, 4 semi-balloon otter trawls and 7 epibenthic sledges between March 1975 and April 1985. Macrourid fishes were numerically dominant at both stations with Coryphaenoides guentheri and Coryphaenoides (Nematonurus) armatus being the most abundant species at M and PS, respectively. In terms of biomass the morid, Antimora rostrata, was dominant at M but C. (N.) armatus was dominant at PS. The only species that showed clear evidence of a seasonal reproductive cycle was C. guentheri. Many species showed no indication of reproducing in the Rockall Trough. The diets of almost all the species are described and considered in relation to the food resources exploited. Investigations on the pelagic and benthic invertebrate faunas at these stations should reveal the extent to which the bottom-living fishes exploit the available resources.     

Parasite faunas,testosterone and secondary sexual traits in male red-winged blackbirds

Summary We examined associations among parasite infections, secondary sexual traits and testosterone in male red-winged blackbirds sampled at the start of the breeding season. Parasites quantified included ectoparasitic lice and mites and endoparasitic blood protozoans, nematodes, trematodes and cestodes. Secondary sexual traits that we quantified included body size, epaulet size and color, song repertoire size and song switching rate, and behavioral responses to male and female models. Overall we found few significant associations between parasites and secondary sexual traits, between secondary sexual traits and testosterone, or between parasites and testosterone. In addition, most parasite taxa appeared to infect birds independently, although the low prevalence (<50%) of many of the parasites meant that our sample sizes were too small to detect weak associations. Our most promising results were obtained for ectoparasitic mites, which tended to occur on birds uninfected with other parasites, on birds with longer epaulets, and on birds with higher levels of testosterone. Epaulet length and testosterone are both probable correlates of dominance in this species. Further research will be required to determine whether there is a causal link between the immunosuppressive effects of testosterone and the mite infections, and between testosterone, epaulet length and male mating success. Correspondence to: P. Weatherhead     

A field test of processed oil shale reclamation strategies designed for minimal use of limited resources

Reclamation of processed oil shale disposal areas in the arid and semi-arid regions of Utah, Colorado and Wyoming faces several challenging problems. Shallow topsoil, harsh climate and limited water supply and low suitability of processed oil shale as a plant growth medium must be addressed if any reclamation plan is to be successful.A prototype reclamation plan that addressed the harsh environmental conditions was proposed early in the development of oil shale in eastern Utah. Studies to validate the reclamation plan were initiated in 1978 on a simulated oil shale disposal area at Anvil Points, Colorado.Four native shrubs, one forb and a grass, were successfully established by planting container-grown transplants into a topsoil-filled V-shaped trench. Supplemental water was provided from an adjacent water harvesting slope. The roots of the transplanted species grew into the adjacent shale from the soil trench, thus indicating their adaptability to the adverse oil shale conditions.Support for this research was provided by the White River Shale Corporation, Salt Lake City, Utah.     

Site fidelity and territorial movements of males in a rapidly declining population of yellow-headed blackbirds

We tested several hypotheses to explain low between-year territory fidelity in a breeding population of yellow-headed blackbirds (Xanthocephalus xanthocephalus). During a 5-year study the population of territorial males declined by two-thirds and some of the marshes that supported territories significantly deteriorated. Individual males held territories and bred for an average of 1.9 years. Of males that bred for at least 2 years, 30% skipped owning a territory in the study area during at least 1 year of their breeding lifetimes. Our information suggests that they may have bred outside of the area in those years. Of males with territories in two or more breeding seasons, 60% changed breeding marshes at least once. Males changed territories during 42.9% of between-year opportunities to do so. We found no support for the hypotheses that male yellow-headed blackbirds: (1) are more likely to move when territory density is low; (2) are likely to abandon territories that are deteriorating; or (3) change territories to improve their reproductive success. We suggest three non-mutually exclusive explanations for the yellow-headed blackbird's weak site fidelity: (1) it is a response to habitat deterioration and to other factors that may be causing the population's decline; (2) the males, being migratory, make fresh settlement decisions each year after they arrive on the breeding grounds in the general vicinity of their previous year's breeding; (3) yellow-headed blackbirds may have evolved in, and be adapted to, highly unstable habitats, moving frequently in response to changes in local breeding site conditions. Correspondence to: L.D. Beletsky     

Comparative studies on the metabolism of shallow-water and deep-sea marine fishes. V. Effects of temperature and hydrostatic pressure on oxygen consumption in the mesopelagic zoarcid Melanostigma pammelas

Measurements have been made of routine oxygen consumption rates ( ) of the mesopelagic deep-sea zoarcid fish Melanostigma pammelas. Determinations were made over ecologically relevant ranges of 3 variables; temperature (3° to 10°C), hydrostatic pressure (1 to 170 atm), and oxygen partial pressure (1 to 160 mm Hg). Weight-specific s were uniformly low. Of the 3 test variables, only temperature had significant metabolic effects within the ranges studied. Q₁₀'s were 6.75 between 3° and 5°C. 1.47 between 5° and 7°C, and 17.4 between 7° and 10°C. These Q₁₀'s were constant over the hydrostatic pressure range studied. Between 3° and 7°C the fish regulated their rates of oxygen consumption down to PO₂'s comparable to those occurring in their natural environments (6 to 12 mm Hg). The showed no capacity to tolerate anoxic conditions. The physiological and ecological significance of these results is discussed, particularly with reference to thermal effects and to the basis of survival of this fish in the oxygen minimum layers of the eastern Pacific Ocean. Since it is possible to maintain M. pammelas in the laboratory for extended periods of time (over 12 months) it could serve as the basis for many interesting studies of deep-sea fish biology.