How well do predators adjust to climate-mediated shifts in prey distribution? A study on Australian water pythons

Climate change can move the spatial location of resources critical for population viability, and a species' resilience to such changes will depend upon its ability to flexibly shift its activities away from no-longer-suitable sites to exploit new opportunities. Intuition suggests that vagile predators should be able to track spatial shifts in prey availability, but our data on water pythons (Liasisfuscus) in tropical Australia suggest a less encouraging scenario. These pythons undergo regular long-range (to >10 kmin) seasonal migrations to follow flooding-induced migrations by their prey (native dusky rats, Rattus colletti). However, when an extreme flooding event virtually eliminated rats for a three-year period, the local pythons did not disperse despite the presence of abundant rats only 8 km away; instead, many pythons starved to death. This inflexibility suggests that some vagile species that track seasonally migrating prey may do so by responding to habitat attributes that have consistently predicted prey availability over evolutionary time, rather than reacting to proximate cues that signal the presence of prey per se. A species' vulnerability to climate change will be increased by an inability to shift its activities away from historical sites toward newly favorable areas.     

River network structure shapes interannual feedbacks between adult sea lamprey migration and larval habitation

Adult sea lampreys (Petromyzon marinus) migrating upstream to spawn follow a pheromone released by instream larvae. The size (i.e. flow) of a tributary dilutes the concentration of this pheromone, such that the downstream propagation pattern of larval pheromone must be influenced by patterns in the relative sizes and numbers of confluent tributaries. We developed an individual-based model to explicitly test the resulting hypothesis that river network structure influences the migration decisions of adult lampreys following the larval pheromone, and in turn the distribution of larvae. First, we initialized the model using randomly generated river networks, and found a strong positive relationship between network diameter and larval aggregation. Larvae aggregated over time, and the degree and rate of this aggregation depended on network diameter. Second, we initialized the model using a river network based on the Muskegon River, Michigan, and compared model-generated larval distribution to available field survey data. We found a significant correlation between model-generated larval abundance and field-measured larval densities (r₂ = 0.54; p < 0.0001). We also found an inverse relationship between subwatershed area and the degree to which path-dependent effects influenced larval abundance in that subwatershed. Our results overall suggest that larval distribution across a watershed results from a system of context-dependent interannual feedbacks shaped by network structure and the past migratory and spawning behavior of adults.     

Modelling landscape effects on density-contact rate relationships of deer in eastern Alberta: Implications for chronic wasting disease

Managing wildlife diseases requires an understanding of disease transmission, which may be strongly affected by host population density and landscape features. Transmission models are typically fit from time-series disease prevalence data and modelled based on how the contact rate among hosts is affected by density, which is often assumed to be a linear (density-dependent transmission) or constant (frequency-dependent transmission) relationship. However, long-term time-series data is unavailable for emerging diseases, and this approach cannot account for independent effects of landscape. We developed a mechanistic model based on ecological data to empirically derive the contact rate-density relationship in white-tailed and mule deer in an enzootic region of chronic wasting disease (CWD) in Alberta, Canada and to determine whether it was affected by landscape. Using data collected from aerial surveys and GPS-telemetry, we developed empirical relationships predicting deer group size, home range size, and habitat selection to iteratively simulate deer distributions across a range of densities and landscapes. We calculated a relative measure of total per-capita contact rate, which is proportional to the number of other deer contacted per individual per unit time, for each distribution as the sum of pairwise contact rates between a target deer and all other individuals. Each pairwise contact rate was estimated from an empirical relationship developed from GPS-telemetry data predicting pairwise contact rates as a function of home range overlap and landscape structure. Total per-capita contact rates increased as a saturating function of density, supporting a transmission model intermediate between density- and frequency-dependent transmission. This pattern resulted from group sizes that reached an asymptote with increasing deer density, although this relationship was mediated by tree and shrub coverage in the landscape, such that in heavily wooded areas, the contact rate saturated at much lower densities. These results suggest that CWD management based on herd reductions, which require a density-dependent contact rate to be effective, may have variable effects on disease across a single management region. The novel mechanistic approach we employed for estimating effects of density and landscape on transmission is a powerful complement to typical data-fitting approaches for modelling disease transmission.     

A general approach to the analysis of habitat selection

The investigation of animal habitat selection aims at the detection of selective usage of habitat types and the identification of covariates influencing their selection. The results not only allow for a better understanding of the habitat selection process but are also intended to help improve the conservation of animals. Usually, habitat selection by larger animals is assessed by radio-tracking or visual observation studies, where the chosen habitat is determined for some animals at a set of specific points in time. Hence the resulting data often have the following structure: a categorical variable indicating the habitat type selected by an animal at a specific point in time is repeatedly observed and will be explained by covariates. These may either describe properties of the habitat types currently available and/or properties of the animal. In this paper, we present a general approach to the analysis of such data in a categorical regression setup. The proposed model generalizes and improves upon several of the approaches previously discussed in the literature. In particular, it accounts for changing habitat availability due to the movement of animals within the observation area. It incorporates both habitat- and animal-specific covariates, and includes individual-specific random effects to account for correlations introduced by the repeated measurements on single animals. Furthermore, the assumption that the effects are linear can be dropped by including the effects in nonparametric manner based on a penalized spline approach. The methodology is implemented in a freely available software package. We demonstrate the general applicability and the potential of the proposed approach in two case studies: The analysis of a songbird community in South-America and a study on brown bears in Central Europe.     

Leaf ontogeny interacts with Bt modification to affect innate resistance in GM aspens

Bioassays with a non-target slug (Deroceras spp.) and chemical analyses were conducted using leaf tissue from already existing genetically modified insect-resistant aspen trees to examine whether genetic modifications to produce Bacillus thuringiensis (Bt) toxins could affect plant phytochemistry, which in turn might influence plant–herbivore interactions. Three major patterns emerged. First, two independent modifications for Bt resistance affected the phytochemical profiles of leaves such that both were different from the isogenic wild-type (Wt) control leaves, but also different from each other. Among the contributors to these differences are substances with a presumed involvement in resistance, such as salicortin and soluble condensed tannins. Second, bioassays with one Bt line suggest that the modification somehow affected innate resistance (“Innate” is used here in opposition to the “acquired” Bt resistance) in ways such that slugs preferred Bt over Wt leaves. Third, the preference test suggests that the innate resistance in Bt relative to Wt plants may not be uniformly expressed throughout the whole plant and that leaf ontogeny interacts with the modification to affect resistance. This was manifested through an ontogenetic determined increase in leaf consumption that was more than four times higher in Bt compared to Wt leaves. Our result are of principal importance, as these indicate that genetic modifications can affect innate resistance and thus non-target herbivores in ways that may have commercial and/or environmental consequences. The finding of a modification–ontogeny interaction effect on innate resistance may be especially important in assessments of GM plants with a long lifespan such as trees.     

A uniform fish consumption advisory protocol for the Ohio River

ORSANCO and the six Ohio River main stem states have been working to align states' fish consumption advisories (FCAs) to enhance the value of advice issued to the public. To achieve this goal, ORSANCO worked closely with a panel consisting of state and USEPA representatives. The result of this effort is the Ohio River Fish Consumption Advisory Protocol (ORFCAP). The ORFCAP represents a single set of variables agreed upon by the panel that allows for a standardized protocol to create advisory thresholds to which states can defer to issue consumption advice for the Ohio River. The ORFCAP identifies ORSANCO as a clearinghouse for data which will be distributed to the panel for decision making. Other components include identifying primary contaminants of concern (PCBs and mercury) and dividing the river into four reporting units. The protocol was developed to issue FCAs for the protection of sensitive populations using five advisory groupings for PCBs and four for mercury. Specific variables used in the calculation of advisory thresholds such as health protection values, cooking reductions, average meal sizes, etc., were selected by the panel. Lastly, the protocol calls for FCA decisions to be based on analysis of the most recent 10?years of data for each species in each reporting unit to determine size class needs and advisory groupings. Upon pending implementation of the protocol by the main stem states, these decisions will be made annually through a series of discussions involving ORSANCO, the panel, and other appropriate state personnel.     

Assessing possible visitor-use impacts on water quality in Yosemite National Park, California

There is concern that visitor-use associated activities, such as bathing, dish washing, wastewater production, and stock animal use near lakes and streams, could cause degradation of water quality in Yosemite National Park. A study was conducted during 2004-2007 to assess patterns in nutrient and Escherichia coli (E. coli) concentrations in the Merced and Tuolumne Rivers and characterize natural background concentrations of nutrients in the park. Results indicated that nutrient and E. coli concentrations were low, even compared to other undeveloped sites in the United States. A multiple linear regression approach was used to model natural background concentrations of nutrients, with basin characteristics as explanatory variables. Modeled nitrogen concentrations increased with elevation, and modeled phosphorus concentrations increased with basin size. Observed concentrations (±uncertainty) were compared to modeled concentrations (±uncertainty) to identify sites that might be impacted by point sources of nutrients, as indicated by large model residuals. Statistically significant differences in observed and modeled concentrations were observed at only a few locations, indicating that most sites were representative of natural background conditions. The empirical modeling approach used in this study can be used to estimate natural background conditions at any point along a study reach in areas minimally impacted by development, and may be useful for setting water-quality standards in many national parks.     

Fire history and tree recruitment in the Colorado Front Range upper montane zone: implications for forest restoration

Forests experiencing moderate- or mixed-severity fire regimes are presumed to be widespread across the western United States, but few studies have characterized these complex disturbance regimes and their effects on contemporary forest structure. Restoration of pre-fire-suppression open-forest structure to reduce the risk of uncharacteristic stand-replacing fires is a guiding principle in forest management policy, but identifying which forests are clear candidates for restoration remains a challenge. We conducted dendroecological reconstructions of fire history and stand structure at 40 sites in the upper montane zone of the Colorado Front Range (2400-2800 m), sampled in proportion to the distribution of forest types in that zone (50% dominated by ponderosa pine, 28% by lodgepole pine, 12% by aspen, 10% by Douglas-fir). We characterized past fire severity based on remnant criteria at each site in order to assess the effect of fire history on tree establishment patterns, and we also evaluated the influence of fire suppression and climate. We found that 62% of the sites experienced predominantly moderate-severity fire, 38% burned at high severity, and no sites burned exclusively at low severity. The proportion of total tree and sapling establishment was significantly different among equal time periods based on a chi-square test, with highest tree and sapling establishment during the pre-fire-suppression period (1835-1919). Superposed epoch analysis revealed that fires burned during years of extreme drought (95% CI). The major pulse of tree establishment in the upper montane zone occurred during a multidecadal period of extreme drought conditions in the Colorado Front Range (1850-1889), during which 53% of the fires from the 1750-1989 period burned. In the upper montane zone of the Colorado Front Range, historical evidence suggests that these forests are resilient to prolonged periods of severe drought and associated severe fires.     

Provenance, life span, and phylogeny do not affect grass species' responses to nitrogen and phosphorus

Successful conservation management requires an understanding of how species respond to intervention. Native and exotic species may respond differently to management interventions due to differences arising directly from their origin (i.e., provenance) or indirectly due to biased representations of different life history types (e.g., annual vs. perennial life span) or phylogenetic lineages among provenance (i.e., native or exotic origin) groups. Thus, selection of a successful management regime requires knowledge of the life history and provenance-bias in the local flora and an understanding of the interplay between species characteristics across existing environmental gradients in the landscape. Here we tested whether provenance, phylogeny, and life span interact to determine species distributions along natural gradients of soil chemistry (e.g., soil nitrogen and phosphorus) in 10 upland prairie sites along a 600-km latitudinal transect running from southern Vancouver Island in British Columbia, Canada, to the Willamette Valley in Oregon, USA. We found that soil nitrate, phosphorus, and pH exerted strong control over community composition. However, species distributions along environmental gradients were unrelated to provenance, life span, or phylogenetic groupings. We then used a greenhouse experiment to more precisely measure the response of common grass species to nitrogen and phosphorus supply. As with the field data, species responses to nutrient additions did not vary as a function of provenance, life span, or phylogeny. Native and exotic species differed strongly in the relationship between greenhouse-measured tolerance of low nutrients and field abundance. Native species with the greatest ability to maintain biomass production at low nutrient supply rates were most abundant in field surveys, as predicted by resource competition theory. In contrast, there was no relationship between exotic-species biomass at low nutrient levels and field abundance. The implications of these findings for management of invasive species are substantial in that they overturn a general belief that reduction of nutrient supplies favors native species. The idiosyncratic nature of species response to nutrients in this study suggests that manipulation of nutrient supplies is unlikely to alter the overall balance between native and exotic species, although it may well be useful to control specific exotic species.