Ecosphere最新文献

Inanimate surfaces that are contaminated with infectious pathogens are common sources of spread for many communicable diseases. Understanding how ambient temperature alters the ability of pathogens to remain viable on these surfaces is critical for understanding how fomites can contribute to seasonal patterns of disease outbreaks. House finches (Haemorhous mexicanus) experience fall and winter outbreaks of mycoplasmal conjunctivitis, caused by the bacterial pathogen Mycoplasma gallisepticum (MG). Although bird feeder surfaces serve as an indirect route of MG transmission between sick and healthy individuals, the contributions of feeders to MG transmission in the wild will depend on how ambient temperature affects viability and pathogenicity of MG on feeder surfaces over time. Here, we used two experiments, with identical initial design, to assess such temperature effects. For both experiments, we pipetted equal amounts of MG onto replicate feeder ports held at night-day temperatures representing summer (22–27°C) or winter (4–9°C). We allowed MG to incubate on feeders at either temperature and swabbed remaining inocula from surfaces at 0, 1, 2, 4, or 7 days post-inoculation of the feeder, with each replicate feeder port only swabbed at a single time point. In the first study, we analyzed swabs using a culture-based assay and found that MG incubated at colder versus warmer temperatures maintained higher viability on feeder surfaces over time. In the second study, we replicated the same experimental design but used MG swabs from feeder surfaces to inoculate wild-caught, pathogen-naïve birds and measured resulting disease severity and pathogen loads to determine pathogenicity. We found that MG remained pathogenic on feeder surfaces at cold ambient temperatures for up to one week, much longer than previously documented. Further, MG was significantly more pathogenic when incubated on feeders in colder versus warmer temperatures, with the strongest effects of temperature present after at least four days of incubation on feeder surfaces. Overall, cold ambient temperatures appear to alter the role of fomites in the MG transmission process, and temperature likely contributes to seasonal disease dynamics in this system and many others.

The longleaf pine (Pinus palustris) savanna ecosystem is an imperiled, fire-dominated community that supports exceptionally high levels of species richness and endemism. Area of this community has declined by more than 95% due to unsustainable logging, fire suppression, and changes in land-use practices. In recent decades, efforts to restore fire-dominated communities like longleaf pine savanna have gained popularity, especially in light of benefits to charismatic species like the northern bobwhite (Colinus virginianus). Although reptiles are important members of this ecological community, far less information exists as to how this group responds to longleaf pine management, especially when game bird conservation is a primary management focus. Although bobwhite management in these systems is mostly synonymous with longleaf pine restoration, additional conservation practices aimed at game birds (promoting fallow fields, supplemental feeding, meso-carnivore control, cross sectional mowing, etc.) might affect the extent to which squamates benefit from habitat management. To better understand how squamate reptiles may benefit from longleaf pine savanna managed for northern bobwhites, we surveyed for six-lined racerunners (Aspidoscelis sexlineata) across a large, contiguous tract of longleaf pine with varied land cover characteristics, managed to maximize the conservation of northern bobwhites. Racerunner detection probability on transect surveys was low ($��\hat{p}�$ = 0.23); however, occupancy probability was relatively high ($�\widehat{ᴪ}$ = 0.60) across the property and driven by percent open ground (positive; 25-m scale), percent grass cover (negative; 25-m scale), and percent wetland (negative; 100-m scale). Our findings support those of past studies about six-lined racerunners in longleaf pine savannas suggesting the species thrives in the context of a short fire rotation (e.g., 2–3 years), even when game bird management is a primary objective of conservation efforts. Racerunners may also specialize on microhabitats (e.g., upland areas with relatively high bare ground cover) that occur most frequently in recently burned portions of bobwhite management units.

Climate-induced shifts in mosquito phenology and population structure have important implications for the health of humans and wildlife. The timing and intensity of mosquito interactions with infected and susceptible hosts are a primary determinant of vector-borne disease dynamics. Like most ectotherms, rates of mosquito development and corresponding phenological patterns are expected to change under shifting climates. However, developing accurate forecasts of mosquito phenology under climate change that can be used to inform management programs remains challenging despite an abundance of available data. As climate change will have variable effects on mosquito demography and phenology across species it is vital that we identify associated traits that may explain the observed variation. Here, we review a suite of modeling approaches that could be applied to generate forecasts of mosquito activity under climate change and evaluate the strengths and weaknesses of the different approaches. We describe four primary life history and physiological traits that can be used to constrain models and demonstrate how this prior information can be harnessed to develop a more general understanding of how mosquito activity will shift under changing climates. Combining a trait-based approach with appropriate modeling techniques can allow for the development of actionable, flexible, and multi-scale forecasts of mosquito population dynamics and phenology for diverse stakeholders.

Facultative anadromous salmonids may alter migratory behavior to mitigate against detrimental infections of aquaculture-derived salmon lice (Lepeophtheirus salmonis); however, this likely incurs negative growth and fitness consequences. This flexibility in migratory behavior also creates analytical challenges in estimating lice infestation levels and the consequences of exposure. We utilized simulated individual migration trajectories of facultatively anadromous brown trout (Salmo trutta) (N = 8049), generated from spatial-temporal fjord-use models fitted to empirical tracking data (N = 517). These trajectories were superimposed with open-access spatial-temporal modeled lice densities. Individual accumulated lice exposure and infestation were simulated over a 6-month period for smolts and annually for veteran migrant life-stages. The degree of lice-induced mortality was estimated according to year (2013–2015), population (N = 5), and life-stage of brown trout, within a semi-enclosed fjord system (Sognefjorden, Norway). A gradient of lice was spatially distributed throughout the fjord. Highest densities were modeled in the outer-fjord at a closer vicinity to aquaculture facilities. Accordingly, estimates of accumulated lice infestation were higher for individuals that underwent long-distance migrations, residing for longer in the outer-fjord, with limited differences observed between years. As most brown trout remained in the inner-fjord, an area protected from aquaculture, individual accumulated levels of lice exposure and infestation were low, resulting in infestation estimates largely below critical-mortality thresholds. The fraction of total mortality attributed to lice during sea-sojourn was greater for long-distance migrants (smolts: 25.3%; veteran migrants: 14.8%) versus those remaining within the inner-fjord (smolts: 14.7%; veteran migrants: 1.7%). This resulted in an unequal contribution of lice to total mortality among populations (range: 3.3%–34.3%). Despite an equal distribution of lice exposure for all populations within the fjord, diverse mortality consequences among populations were estimated, largely resulting from individual selection of migration trajectory. Therefore, generic models of lice effects on facultative anadromous salmonids should be used with caution. Instead, the application of simulated migration trajectories to incorporate flexible behavior at the individual level is suggested. The findings indicate that Sognefjorden brown trout may have reduced their seaward migration extent to avoid direct mortality from salmon lice. This emphasizes the importance of monitoring and management actions to preserve selection for anadromy.

Grazing can impart long-lasting changes in vegetated ecosystems. How ecosystems respond to herbivory depends on the ecological and evolutionary histories of their foundational species. The overall ecosystem functioning and associated biodiversity depend on these responses but there is still little understanding on how the intensity and duration of herbivory interact and impact vegetated ecosystems. We experimentally tested in the field the responses of three seagrass species with distinct life history traits to increasing intensities of herbivory over time. Specifically, we assessed structural responses (i.e., canopy height and shoot density) to reflect the ecosystem state. Additionally, we used mechanistic models to assess induced and constitutive responses in the different seagrass species. Results show that seagrasses coped with herbivory differentially in relation to their life history traits. Posidonia oceanica (persistent species) was resistant and only registered declines in canopy height, whereas both canopy heigh and shoot density rapidly decreased for Cymodocea nodosa (intermediate-colonizing species) and Zostera noltei (colonizing species). Seagrasses also differed in the type of structural response, with the colonizing species experiencing reductions in shoot density, and the persistent P. oceanica registering declines in canopy height. After months of exposure to cumulative herbivory, all three species showed signs of stability. Interestingly, none of the species disappeared completely even when exposed to extreme herbivory. Mechanistic models indicate that herbivory-induced responses are a potential explanation for these patterns. This study suggests that given the long evolutionary history of herbivory, some seagrasses may be remarkably well adapted to both intense and cumulative herbivory.

Marginal populations of temperate species at the leading edge of their range will likely play a key role at the boreal-temperate ecotone (BTE) in the face of climate changes. In eastern North America, red maple (Acer rubrum L.) is the most abundant temperate tree species encroaching into the boreal forest. In order to provide useful insights about possible responses to climate change and anticipate the formation of new assemblages, this study relies on long-term Holocene data from forest soil wood macrofossils (charcoal and ligneous remains) and contemporary stand analyses to assess the postglacial origin and modern-day dynamics of red maple at its leading edge within the BTE. We sampled the soils of eight marginal red maple stands. Macroscopic charcoal particles and ligneous remains were identified using microanatomical characteristics. Macrofossils of temperate tree species were radiocarbon dated to reconstruct their long-term stand-scale history. Contemporary dynamics (<200 years) were assessed by analyzing tree size structure of all stems within 400 m² plots, minimal stand age from tree-ring dating, as well as the recent occurrence of fire and logging from published ecoforest data. White pine (Pinus strobus L.), the only other temperate tree species that was identified, was present 6500–4000 years ago, during the mid-Holocene thermal maximum but decreased during the cooler and fire-prone late-Holocene Neoglacial (4000 years ago to present). By contrast, red maple was found at its current northern limit since the last 4000 years. Modern-day marginal red maple stands are self-regenerating populations that established following a recent stand-replacing disturbance (wildfire or clearcut). The present-day increase of anthropogenic disturbances within the BTE could mirror the Neoglacial increase in fire activity that fostered red maple during the Holocene. We thus predict that red maple is poised to increase in abundance within the BTE, which should facilitate the northward establishment of other temperate deciduous species into the boreal forest prompted by the new conditions brought about by anthropogenic or climate change-induced disturbances.

Savannas are the major biome in tropical regions of the globe, defined as sparsely wooded regions with a continuous herbaceous layer of mainly C₄ grasses where rainfall is distinctly seasonal. Fire is a common feature of most savannas. The largest protected areas of savannas are found in sparsely populated monsoonal northcentral Australia with strong annual wet and dry seasons. The most common vegetation type is relatively intact, tall (<15 m), open forests where Eucalyptus canopy trees form the basic structure. Over the past half century, traditional indigenous fire regimes were largely replaced by contemporary fires where individual trees may experience fire as often as 3 out of 5 years. The potential for long-term persistence of the canopy tree populations is an open question. A stage-based population model of the canopy trees was previously developed to address this question, drawing on data from three decades of experimental field studies wherein the survival, growth, and reproduction of individual marked trees were recorded under different seasonal fires and understory types to produce transition matrices among eight life history stages, and used to calculate population growth rates (λ). Here, we apply that model to determine how λ varies across a range of fire return intervals from 1 to 12 years for both early and late dry season fires, in two different understory types. We also explore the sensitivity of λ to two key life history parameters: recruitment and seedling survival. Minimum fire return intervals of 2–5 years were generally required for λ ≥1 that would allow populations to persist; these were shorter with stochastic year-to-year timing of fires and with higher recruitment rates. Uniquely, under certain conditions, there was also a maximum fire return interval above which λ <1, creating a “window” of fire return intervals that allowed canopy tree populations to persist. Mechanisms underpinning results as well as implications for savanna structure, alternate states, cyclical dynamics, future research, and management by fire are discussed.

Grassland bird populations are declining steeply, reflecting the degradation and loss of native grassland habitats. To assess how grazing management affects declining grassland bird populations, we compared breeding avifaunal communities in adaptive multi-paddock (AMP) grazed and continuously grazed (CG) pastures in the Southeastern United States. AMP grazing involves alternating very short grazing periods at high animal densities with prolonged recovery periods across many small paddocks. Both the AMP and CG paddocks attracted obligate grassland birds during the breeding season; however, AMP-grazed paddocks supported significantly higher detection of four obligate grassland breeding bird species. We used distance sampling techniques to account for differences in detectability for each species. The resulting densities for the grassland guild and Eastern Meadowlark as a species both revealed significantly higher densities within the AMP versus CG paddocks. Despite significantly more unadjusted detections of confirmed breeding ecotonal species, such as Blue Grosbeak, Eastern Bluebird, Brown Thrasher, Yellow-breasted Chat, Eastern Towhee, Loggerhead Shrike, and Field Sparrow in AMP versus CG paddocks, no significant difference was found in the ecotonal guild after adjusting densities using effective detection radii. The CG paddocks supported fewer obligate grassland and ecotonal birds, with some exceptions (e.g., higher adjusted density of Eastern Bluebirds in CG) but supported comparable overall bird species richness. AMP grazing practices offer a viable strategy for increasing the diversity and abundance of obligate grassland and ecotonal breeding birds within existing cattle-grazed landscapes in the Southeastern United States.

Rapid urbanization is drastically altering ecosystem processes in landscapes around the world. In particular, suburban residential neighborhoods comprise novel ecosystems with water and nutrient inputs that differ greatly from the surrounding land area. These impacts generate concern over the sustainability of urban ecosystems, especially whether they will be characterized by net carbon gain or loss over time. To address this knowledge gap, we established a chronosequence of residential yards in Southern California to test how urban soils change after development. We predicted that urbanized soils would experience shifts in physical characteristics and microbial function over time consistent with ecological succession theory, but residential soils would maintain novel moisture and nutrient regimes compared to undeveloped soils, never “recovering” to a pre-developed state. We compared different vegetation types to quantify impacts of homeowner landscaping choices and characterized yard soils and their microbial communities. We found that yard soils were nutrient- and moisture-enriched compared to an adjacent undeveloped ecosystem, and turfgrass was associated with higher levels of water and nitrogen. Despite high respiration rates, yard soils accumulated carbon and nitrogen over time. We conclude that suburban residential soils comprise dynamic and heterogeneous ecosystems that are highly influenced by landscaping choices and management practices, and warrant closer study at small management-relevant scales.

Habitat loss and fragmentation are a growing threat to wildlife, and a better understanding of these landscape processes is needed to mitigate their effects on species populations. Grassland biomes are among the most imperiled ecosystems in the world, and grassland birds are experiencing significant population declines in North America. Understanding how species respond to differences in resource availabilities across spatiotemporal extents is critical to determining animals' distributions. Here, we investigated the relationship of landscape attributes to spatiotemporal distribution of a grassland bird, the ring-necked pheasant (Phasianus colchicus), which has experienced population declines in the Midwest, USA. Pheasant declines have been attributed to two anthropogenic stressors, land use change and climate change. In this study, we evaluated the effect of landscape attributes (composition and configuration) on the home-range size and resource selection of pheasants. We used a 95% fixed kernel estimator to estimate home-range size and identified scales at which landscape features influenced home-range sizes. We quantified landscape features within radii of 250, 500, and 1000 m (i.e., local to broader spatial scales) from the home-range center. We also used resource selection functions to predict the home-range placement (second order) and resource selection within home ranges (third order) of pheasants during winter, pre-nesting, and nesting seasons. We developed multi-scale predictions of pheasant resource selection and identified wetlands, grasslands, Conservation Reserve Program (CRP) grasslands, and small grains as land cover types used by pheasants to fulfill their life requirements. Our results indicated home ranges were more likely to be in a landscape with more CRP, wetlands, and grasslands; more connected grasslands; and a greater number of grassland patches. Pheasants also selected heterogeneous landscape and avoided row crops at both orders of selection. Maintaining habitat heterogeneity, by managing landscapes composed of a high proportion of grasslands and CRP surrounded by small grains and wetlands, could enhance the benefits of local management practices for pheasants. Collectively, insights obtained from our study can advance habitat conservation efforts for similar grassland birds and consequently are of broad utility to biologists and wildlife managers.