Ecology最新文献

The importance of trait variation has long been recognized in ecological and evolutionary research. The divergence of sexually dimorphic traits (e.g., body size, morphology, behavior, etc.) is primarily attributed to sexual selection, and sexual dimorphism can have consequences for diets and habitat use. Recent evidence for one aquatic predator species (adult newts; Notophthalmus viridescens) suggests that trait differences and habitat partitioning between the sexes may be important in structuring zooplankton communities. However, newts are known to increase amphibian diversity within pond communities via keystone predation. Yet, no data are available on differentiating potentially sexually dimorphic effects of newts on larval amphibian communities. Thus, we conducted a series of mesocosm experiments to determine the effects of sexual dimorphism of adult newts on larval amphibian communities. Based on previous work with newts and zooplankton, we hypothesized that male and female newts would have differing effects on prey communities. We found that female newts consumed one prey species more than male newts did and no newt treatments. There were no differences between the sexes in prey consumption of another prey species. Size at metamorphosis was greater in the presence of newts (either male or female) for wood frogs and in the presence of female newts for spotted salamanders in comparison with no newt treatments. Our findings indicate that sexual dimorphism within a known keystone predator can have differential effects on prey. Indeed, our results indicate that while the effects of predators on one response (survival) can differ between sexes, the impacts on another response (prey fitness; measured as size at metamorphosis) were similar. Our research to understand the effects of sexual dimorphism is timely as sex ratios of predators may become skewed in nature due to anthropogenic change. If intraspecific differences exist via top-down effects, then downstream impacts on prey communities may go unnoticed.

Phenotypic plasticity in body growth enables organisms to cope with unpredictable paucities in resource availability. Growth traits influence survival and reproductive success, and thereby, population persistence, and early-life resource availability may govern lifetime patterns in growth, reproductive success, and survival. The influence of early-life environment is decidedly consequential for indeterminately growing ectotherms, which rely on available resources and ambient temperatures to maximize fitness throughout life. Using 17 years of mark–recapture data, we evaluate the effects of resource availability on patterns in growth for populations of western terrestrial garter snakes (Thamnophis elegans), which differ along pace-of-life continuums into fast- and slow-living ecotypes. We use an adaptation of the von Bertalanffy estimator to fit structural growth models and linear predictors for body condition to analyze the consequences of annual and early-life prey availability. Snakes from resource-poor early-life environments are primed to exploit conditions in high-prey environments later in life. Slow pace-of-live animals exhibit a greater capacity for compensatory strategies in structural growth, while body condition was best explained by a complex interaction across males and non-gravid females between prey availability and ecotype. Our findings highlight the importance of accounting for context-dependent early-life environments as well as sex-specific reproductive demands when evaluating population traits.

Seasonal variations in foliar nutrient concentrations are an important strategy of plants to adapt to different climates and availabilities of soil nutrients. Gaps in our knowledge, however, remain in both the seasonality of the concentrations of multiple nutrients in plant leaves and their spatial pattern on a large scale. We compiled data on foliar concentrations of nine essential nutrients (N, P, K, Ca, Mg, Fe, Mn, Zn, and Cu) in woody plants in China and evaluated the characteristics and latitudinal patterns of their seasonal variability (i.e., seasonality). Foliar concentrations of mobile nutrients (N, P, K, and Zn) in deciduous broadleaf woody plants decreased significantly during the growing season, but nonmobile nutrients (Ca and Mn) continued to accumulate. In contrast, the foliar nutrient concentrations in evergreen broadleaves and conifers generally showed no significant seasonal trend. The seasonality of foliar nutrient concentration was weaker for the nutrients with higher foliar concentrations, supporting the hypothesis of seasonal stability of high-demand nutrients. The seasonality of foliar nutrient concentration was stronger for deciduous than evergreen plants, while the effect of plant phylogeny was not statistically significant. The seasonality of foliar N and P concentrations increased with latitude in the deciduous broadleaf woody plants, but evergreen plants showed no significant latitudinal trend. The spatial patterns of seasonality for foliar N and P concentrations were significantly explained by climate and foliar habit. These findings improve our understanding of the seasonality of plant foliar concentrations of multiple nutrients as a strategy to adapt to varying climatic conditions.

Many vector-borne diseases are sensitive to changes in land use and climate; hence, it is important to understand the factors that govern the vector populations. Ixodid ticks, which serve as vectors for multiple diseases, have a slow life cycle compared with many of their hosts. The observable questing population represents only a fraction of the total tick population and may include overlapping cohorts in each stage. The duration of each life stage (larvae, nymph, and adult) is variable and depends on factors such as the seasonal timing of questing, development, and host availability. Mathematical models are therefore essential to mediate how complex life cycle transitions and host interactions underpin the seasonal dynamics of the questing tick population. In this study, we develop a seasonal matrix population model for ixodid ticks feeding on a small and large host. The model has 17 stages representing the main life history stages (eggs, larvae, nymphs, and adults) combined with status of feeding, seasonal timing of feeding, and overwintering. The probability of finding a host depends on tick instar and host type, and density regulation is incorporated through limited host capacity. Using a life history representing Ixodes ricinus in Northern Europe as a baseline, we extract seasonal numbers of different parts of the tick population and calculate life history outcomes such as generation time and mean and variance of lifespan and of lifetime reproductive output. These results are compared with an alternative scenario of a southern life history. Secondly, we investigate (1) effects of seasonality in the small host availability on the seasonal numbers of tick stages and (2) effects of varying host availability and utilization of small versus large hosts by larvae and nymphs, on the seasonal numbers of questing ticks. Our results suggest that the small host availability is an important regulating factor through the feeding of larvae. Our model incorporates complex mechanisms underlying the seasonal composition of the tick population. It can be applied to different ixodid tick species and provides a framework for future investigations into intra- and interspecific variation in life history and population dynamics.

Understanding the patterns and drivers of species range shifts is essential to disentangle mechanisms driving species' responses to global change. Here, we quantified local extinction and colonization dynamics of giant pandas (Ailuropoda melanoleuca) using occurrence data collected by harnessing the labor of >1000 workers and >60,000 worker days for each of the three periods (TP1: 1985–1988, TP2: 1998–2002, and TP3: 2011–2014), and evaluated how these patterns were associated with (1) protected area, (2) local rarity/abundance, and (3) abiotic factors (i.e., climate, land-use, and topography). We documented a decreased rate (from 0.433 during TP1–TP2 to 0.317 during TP2–TP3) of local extinction and a relatively stable rate (from 0.060 during TP1–TP2 to 0.056 during TP2–TP3) of local colonization through time. Furthermore, the occupancy gains have exceeded losses by a ratio of approximately 1.5 to 1, illustrating an expansion of panda's range at a rate of 1408.3 km²/decade. We also found that pandas were more likely to become locally extinct outside of protected areas, when locally rare in surrounding areas, and when certain biotic conditions were not met (e.g., increased forest cover). Local colonization was less likely in areas with high local rarity, challenging biotic conditions and unprotected area status. As the network of panda reserves expanded and the forest matured, the relative importance of other factors such as climate, biotic factors, and land-use became more influential in determining patterns of local extinction and colonization. Our findings provide insights into the factors governing the expansion of panda's range and illustrate how the relative influence of biotic and abiotic factors can change over time, indicating that effective conservation intervention may be able to mitigate some of the negative impacts of climate change and habitat degradation. This insight extends beyond pandas and highlights the role of conservation interventions can play in building resilience under a changing climate.

Shifting community assembly dynamics are an underappreciated mechanism by which warming will alter plant community composition. Germination timing (which can determine the order in which seedlings emerge within a community) will likely shift unevenly across species in response to warming. In seasonal environments where communities reassemble at the beginning of each growing season, changes in germination timing could lead to changes in seasonal priority effects, and ultimately community composition. We test this expectation by assembling mesocosms of 15 species in one of two orders—“ambient” assembly order or “warmed” assembly order—based on the order in which the constituent species germinated under ambient and warmed conditions. Community composition differed significantly between mesocosms assembled in ambient versus warmed orders. The impact of assembly order on species mean biomass was largely explained by how much earlier (or later) a species arrived in the warmed-order treatment relative to the ambient-order treatment. Species whose germination phenology advanced more under warmed conditions relative to ambient conditions showed greater relative increases in biomass under the warmed assembly treatment. These findings demonstrate that warming can drive community assembly and shape community composition by reordering the relative timing of germination among species. These findings enhance our ability to predict which species are likely to benefit from warming and which may decline based on how warming may shift assembly order, ultimately informing how warming may alter plant communities.

Forests sequester a substantial portion of anthropogenic carbon emissions. Many open questions concern how. We address two of these questions. Has leaf and fine litter production changed? And what is the contribution of old-growth forests? We address these questions with long-term records (≥10 years) of total, reproductive, and especially foliar fine litter production from 32 old-growth forests. We expect increases in forest productivity associated with rising atmospheric carbon dioxide concentrations and, in cold climates, with rising temperatures. We evaluate the statistical power of our analysis using simulations of known temporal trends parameterized with sample sizes (in number of years) and levels of interannual variation observed for each record. Statistical power is inadequate to detect biologically plausible trends for records lasting less than 20 years. Modest interannual variation characterizes fine litter production, and more variable phenomena will require even longer records to evaluate global change responses with sufficient statistical power. Just four old-growth forests have records of fine litter production lasting longer than 20 years, and these four provide no evidence for increases. Three of the four forests are in central Panama, also have long-term records of wood production, and both components of aboveground production are unchanged over 21–38 years. The possibility that recent increases in forest productivity are limited for old-growth forests deserves more attention.

Global warming increases the risk of wildfire and insect outbreaks, potentially reducing the carbon storage function of coarse woody debris (CWD). There is an increasing focus on the interactive effects of wildfire and insect infestation on forest carbon, but the impact of wood-boring beetle tunnels via their effect on the flammability of deadwood remains unexplored. We hypothesized that the presence of beetle holes, at natural densities, can affect its flammability positively through increased surface area and enhanced oxygen availability in the wood. To test this, wood-boring beetle holes were mimicked experimentally in decaying logs of two coniferous species, and flammability variables of these treated logs were compared. We found that wood-boring beetles partly increased the flammability of CWD of both species (via promoting deadwood smoldering combustion) when their holes were parallel with the airflow. Even when accounting for the influences of wood density and cracks, these radial holes continued to have a notable impact on deadwood flammability. While these holes did not make the wildfire more intense, they significantly increased carbon loss during combustion. This suggests that wood-boring beetles will enhance carbon release from deadwood into the atmosphere during wildfire.

A growing body of theoretical studies and laboratory experiments has focused attention on reciprocal feedbacks between ecological and evolutionary processes. However, uncertainty remains about whether such eco-evolutionary feedbacks have an important or negligible influence on natural communities. Thus, recent discussions call for field experiments that explore whether selection on phenotypic variation within populations leads to contemporaneous effects on community dynamics. To help fill this gap, in this study, we test the hypothesis that selection on consumer traits in a population of predatory drilling snails can drive eco-evolutionary dynamics in a rocky intertidal community in California, USA. We first conducted a laboratory selection experiment to raise newly hatched dogwhelks (Nucella canaliculata) on four diet treatments encompassing a range of prey species and shell thicknesses. Snails that survived to adulthood under these diet treatments differed in their capacity to drill thick-shelled mussels. Dogwhelks from these treatment groups were then outplanted to intertidal field cages for 1 year to test whether groups experiencing selection differed in their effects on mussel bed succession. As expected, succession proceeded most rapidly in the reference treatment with dogwhelks excluded. However, successional patterns differed minimally among dogwhelks raised under the different diet treatments. Thus, although our laboratory results suggest that prey can impose selection that leads to rapid adaptation and divergent consumer traits, these feedbacks were not strong enough to result in clear community effects in the field. We propose that a limited range of variation in functional traits within populations, moderate strengths of selection, and a background of substantial abiotic and biotic variation may all act to dampen the potential for strong eco-evolutionary dynamics in this and many other natural communities.

Fungi play a crucial role in aquatic leaf litter decomposition. Aquatic fungi have long been thought to spend the majority of their lives in the water. Here, we explore the possibility of an amphibious life cycle, where phyllosphere fungi spend part of their life cycle in aquatic systems. We used internal transcribed spacer (ITS) fungal sequencing to follow phyllosphere fungi onto submerged litter, and quantitative stable isotope probing (qSIP) to differentiate active and inactive fungi. We found that around 30% of fungi active on aquatic litter entered the stream with the leaf and that these phyllosphere fungi were as active, if not more active than, as the fungi colonizing from the water column. These results demonstrate that phyllosphere fungi are an important part of aquatic fungal communities.