Joseph K. Bump

Wolves modulate soil nutrient heterogeneity and foliar nitrogen by configuring the distribution of ungulate carcasses

Mechanistic links between top terrestrial predators and biogeochemical processes remain poorly understood. Here we demonstrate that large carnivores configure landscape heterogeneity through prey carcass distribution. A 50-year record composed of > 3600 moose carcasses from Isle Royale National Park, Michigan, USA, showed that wolves modulate heterogeneity in soil nutrients, soil microbes, and plant quality by clustering prey carcasses over space. Despite being well utilized by predators, moose carcasses resulted in elevated soil macronutrients and microbial biomass, shifts in soil microbial composition, and elevated leaf nitrogen for at least 2-3 years at kill sites. Wolf-killed moose were deposited in some regions of the study landscape at up to 12x the rate of deposition in other regions. Carcass density also varied temporally, changing as much as 19-fold in some locations during the 50-year study period. This variation arises, in part, directly from variation in wolf hunting behavior. This study identifies a top terrestrial predator as a mechanism generating landscape heterogeneity, demonstrating reciprocal links between large carnivore behavior and ecosystem function.

Stable isotopes, ecological integration and environmental change: wolves record atmospheric carbon isotope trend better than tree rings

Large-scale patterns of isotope ratios are detectable in the tissues of organisms, but the variability in these patterns often obscures detection of environmental trends. We show that plants and animals at lower trophic levels are relatively poor indicators of the temporal trend in atmospheric carbon isotope ratios (δ13C) when compared with animals at higher trophic levels. First, we tested how differences in atmospheric δ13C values were transferred across three trophic levels. Second, we compared contemporary δ13C trends (1961–2004) in atmospheric CO2 to δ13C patterns in a tree species (jack pine, Pinus banksiana), large herbivore (moose, Alces alces) and large carnivore (grey wolf, Canis lupus) from North America. Third, we compared palaeontological (approx. 30 000 to 12 000 14C years before present) atmospheric CO2 trends to δ13C patterns in a tree species (Pinus flexilis, Juniperus sp.), a megaherbivore (bison, Bison antiquus) and a large carnivore (dire wolf, Canis dirus) from the La Brea tar pits (southern California, USA) and Great Basin (western USA). Contrary to previous expectations, we found that the environmental isotope pattern is better represented with increasing trophic level. Our results indicate that museum specimens of large carnivores would best reflect large-scale spatial and temporal patterns of carbon isotopes in the palaeontological record because top predators can act as ecological integrators of environmental change.

Ungulate Carcasses Perforate Ecological Filters and Create Biogeochemical Hotspots in Forest Herbaceous Layers Allowing Trees a Competitive Advantage

Ecological filters and nutrient heterogeneity are important in the function of ecosystems. Herbaceous layers alter forest ecosystems by filtering tree species during early stages of tree reproduction and influencing nutrient cycling. Important aspects about how tree species successfully establish below and extend above this ecological filter are unanswered in forest ecology. We experimentally tested the effects of large ungulate carcasses on the filtering function of herbaceous layers. Even well-utilized carcasses created unexpected disturbances that reduced herbaceous cover, which effectively perforated the herbaceous layer filter that can differentially influence tree reproduction. Carcasses also created lasting biogeochemical “hotspots” in forest soils that may help maintain plant biodiversity by creating resource heterogeneity and shifting competitive relationships. Because the spatial distribution of carcasses is influenced by predators, these data establish an unrecognized link between large carnivores, prey carcasses, and ecosystem processes. This link supports a novel understanding of disturbance by large herbivores in forest ecosystems by demonstrating an important interaction between predator–prey functional traits and tree seedling dynamics on either side of a major ecological filter.

Large herbivores and aquatic–terrestrial links in southern boreal forests

1. Concurrent measurement of population dynamics and associated spatio-temporal patterns of resource flow across aquatic-terrestrial boundaries are rare, yet necessary to understand the consequences of cross-habitat resource flux. Long-term study of the moose Alces alces (L.) population in Isle Royale National Park (Lake Superior, USA) provides an opportunity to examine the patterns of resource flux from aquatic to terrestrial habitats over approximately50 years. 2. We analysed the spatio-temporal dynamics of aquatic-derived nitrogen (N) that moose transfer to terrestrial systems by using excretion models, foraging parameters, moose densities, and moose carcass locations (n = 3616) collected from 1958-2005. 3. Results suggest that moose transfer significant amounts of aquatic-derived N to terrestrial systems, which likely increases terrestrial N availability in riparian zones. A seasonal increase in terrestrial N availability when moose are foraging on N-rich aquatic macrophytes would contrast with the depression of soil N mineralization previously attributed indirectly to moose. 4. Aquatic foraging by moose and moose carcass locations are significantly clustered at multiple scales, indicating that grey wolves Canis lupus (L.) and moose can create concentrated areas of resource transfer due to clustered predation and foraging patterns. 5. This study shows that patterns of faunal-mediated resource transfer can depend significantly on predator-prey dynamics, and that large predators in this system influence herbivore-controlled resource transfer between ecosystems. Given the circumpolar extent of moose, they constitute an important, unquantified aquatic-terrestrial resource vector in boreal systems.

Broadening the ecological context of ungulate–ecosystem interactions: the importance of space, seasonality, and nitrogen

Spatial heterogeneity of soil resources, particularly nitrogen availability, affects herbaceous-layer cover and diversity in temperate forest ecosystems. Current hypotheses predict that ungulate herbivores influence nitrogen availability at the stand scale, but how ungulates affect nitrogen availability at finer spatial scales that are relevant to the herb layer is less understood. We tested the hypothesis that ungulate exclusion reduces the spatial complexity of nitrogen availability at neighborhood scales (1-26 m) apart from mean stand scale effects. This outcome was expected due to a lack of ungulate nitrogenous waste deposition within exclosures and seasonally variable ungulate habitat use. To test this hypothesis we examined spatial patterning of ammonium and nitrate availability, herb-layer cover and diversity, and under-canopy solar radiation using geostatistical models. Our study sites included six stands of eastern hemlock (Tsuga canadensis) forest: three where white-tailed deer (Odocoileus virginianus) were excluded and three that were accessible to deer. Where deer were present, patch sizes of ammonium availability, cover, and diversity were smaller compared to deer exclosures, whereas mean site-level effects were not significant. Within deer exclosures cover and solar radiation were more similar in patch size than were cover and nitrogen availability. Our results suggest that browsing ungulates affect spatial patterns of herb-layer cover and diversity through the excretion of nitrogenous wastes in small, discrete patches. Ungulate-excreted nitrogen deposition and herbivory were concentrated in the dormant season, allowing herb-layer plants a greater opportunity to benefit from nitrogen additions. Therefore, the impact of ungulates on nitrogen cycling in forest ecosystems varies with spatial scale and the seasonal timing of ungulate impacts. In this way, ungulates may function as a seasonally dependent link between fine-scale and landscape-level ecological processes.

Bat-cave catchment areas: using stable isotopes (δD) to determine the probable origins of hibernating bats

The application of stable hydrogen isotope (deltaD) techniques has swiftly advanced our understanding of animal movements, but this progression is dominated by studies of birds and relatively long-distance, north-south migrants. This dominance reflects the challenge of incorporating multiple sources of error into geographic assignments and the nature of spatially explicit deltaD models, which possess greater latitudinal than longitudinal resolution. However, recent progress in likelihood-based assignments that incorporate multiple sources of isotopic error and Bayesian approaches that include additional sources of information may advance finer-scale understanding of animal movements. We develop a stable-isotope method for determining probable origins of bats within hibernacula and show that this method produces spatially explicit, continuous assignments with regional resolution. We outline how these assignments can be used to infer hibernacula connectivity, an application that could inform spatial modeling of white-nose syndrome. Additionally, estimates of seasonal and annual flight distances for many cave-dwelling bat species can be derived from this approach. We also discuss how this application can be used in general to provide insights into variable migratory and foraging strategies within bat populations.

Coordinating Environmental Protection and Climate Change Adaptation Policy in Resource-Dependent Communities: A Case Study from the Tibetan Plateau

Resource-dependent communities are likely to be disproportionately affected by climate change. Yet, natural resource management policies continue to be developed and implemented without considering climate change adaptation. We highlight that this lack of coordination is potentially harmful to natural resources and resource-dependent communities with an example from the Tibetan Plateau, a region where climate is changing rapidly. Tibetan pastoralists inhabit rangelands that are the focus of recent development and management policies that promote fencing, sedentarization, individual rangeland use rights, and the elimination of grazing in some areas. These policies may have a negative effect on herders’ ability to adapt to climate change. China’s National Climate Change Programme lists controlling or eliminating grazing in some areas as key for adaptation to climate change, but experimental results indicate that grazing may buffer the rangelands from the negative effects of warming. These findings indicate that policies that support the well-developed strategies of resource-dependent communities for living in uncertain and variable environments can also enhance adaptation of these social and ecological systems to climate change. We conclude that management and environmental protection policies developed separately from climate change policy face increased failure potential and may decrease the ability of natural resources and the communities that depend upon them to successfully adapt to climate change.

Climate Change and Water Use Partitioning by Different Plant Functional Groups in a Grassland on the Tibetan Plateau

The Tibetan Plateau (TP) is predicted to experience increases in air temperature, increases in snowfall, and decreases in monsoon rains; however, there is currently a paucity of data that examine the ecological responses to such climate changes. In this study, we examined the effects of increased air temperature and snowfall on: 1) water use partitioning by different plant functional groups, and 2) ecosystem CO2 fluxes throughout the growing season. At the individual plant scale, we used stable hydrogen isotopes (δD) to partition water use between shallow- and deep-rooted species. Prior to the arrival of summer precipitation (typically mid-July), snowmelt was the main water source in the soils. During this time, shallow and deep-rooted species partitioned water use by accessing water from shallow and deep soils, respectively. However, once the monsoon rains arrived, all plants used rainwater from the upper soils as the main water source. Snow addition did not result in increased snowmelt use throughout the growing season; instead, snowmelt water was pushed down into deeper soils when the rains arrived. At the larger plot scale, CO2 flux measurements demonstrated that rain was the main driver for net ecosystem productivity (NEP). NEP rates were low during June and July and reached a maximum during the monsoon season in August. Warming decreased NEP through a reduction in gross primary productivity (GPP), and snow additions did not mitigate the negative effects of warming by increasing NEP or GPP. Both the isotope and CO2 flux results suggest that rain drives productivity in the Nam Tso region on the TP. This also suggests that the effects of warming-induced drought on the TP may not be mitigated by increased snowfall. Further decreases in summer monsoon rains may affect ecosystem productivity, with large implications for livestock-based livelihoods.

Where wolves kill moose: the influence of prey life history dynamics on the landscape ecology of predation.

The landscape ecology of predation is well studied and known to be influenced by habitat heterogeneity. Little attention has been given to how the influence of habitat heterogeneity on the landscape ecology of predation might be modulated by life history dynamics of prey in mammalian systems. We demonstrate how life history dynamics of moose (Alces alces) contribute to landscape patterns in predation by wolves (Canis lupus) in Isle Royale National Park, Lake Superior, USA. We use pattern analysis and kernel density estimates of moose kill sites to demonstrate that moose in senescent condition and moose in prime condition tend to be wolf-killed in different regions of Isle Royale in winter. Predation on senescent moose was clustered in one kill zone in the northeast portion of the island, whereas predation on prime moose was clustered in 13 separate kill zones distributed throughout the full extent of the island. Moreover, the probability of kill occurrence for senescent moose, in comparison to prime moose, increased in high elevation habitat with patches of dense coniferous trees. These differences can be attributed, at least in part, to senescent moose being more vulnerable to predation and making different risk-sensitive habitat decisions than prime moose. Landscape patterns emerging from prey life history dynamics and habitat heterogeneity have been observed in the predation ecology of fish and insects, but this is the first mammalian system for which such observations have been made.

Combining citizen science species distribution models and stable isotopes reveals migratory connectivity in the secretive Virginia rail

1. Stable hydrogen isotope (delta D) methods for tracking animal movement are widely used yet often produce low resolution assignments. Incorporating prior knowledge of abundance, distribution or m ...