Ecological Applications最新文献

Intercorrelated aboveground traits associated with costs and plant growth have been widely used to predict vegetation in response to environmental changes. However, whether underground traits exhibit consistent responses remains unclear, particularly in N-rich subtropical forests. Responses of foliar and root morphological and physiological traits of tree and herb species after 8-year N, P, and combined N and P treatments (50 kg N, P, N and P ha⁻¹ year⁻¹) were examined in leguminous Acacia auriculiformis (AA) and nonleguminous Eucalyptus urophylla (EU) forests in southern China. N addition did not significantly impact all leaf and root traits except root N concentration per root length. Root traits responded to P addition more than leaf traits in trees; however, both traits responded similarly to P addition in herbs. Tree species deviated from the expected leaf economics spectrum; however, all species aligned with the root economics spectrum. The P and combined N and P treatments significantly altered the position of principal components analysis of root functional traits for herb species compared to the control. However, these changes did not reflect a classic shift in nutrient acquisition strategy within the root economics spectrum. As leguminous species experienced greater P limitation, AA responded more to P addition than EU; their understories indicated no significant differences. This study reveals how plant aboveground and underground traits adapt to nutrient-rich environments. These findings highlight the importance of incorporating plant underground traits, which show significant and specific responses to nutrient additions, into Earth system models for accurately predicting plant responses to global change.

Plastic pollution threatens almost every ecosystem in the world. Critically, many animals consume plastic, in part because plastic particles often look or smell like food. Plastic ingestion is thus an evolutionary trap, a phenomenon that occurs when cues are decoupled from their previously associated high fitness outcomes. Theory predicts that dominance hierarchies could dictate individual responses to evolutionary traps across social environments, but the social dimension of evolutionary trap responses has rarely been investigated. We tested how variation in group size influences the formation of dominance relationships and, in turn, how these dominance relationships drive differences in foraging behavior in Western mosquitofish (Gambusia affinis). This included foraging for a variety of familiar and novel food-like items, including microplastics. Overall, dominant individuals were often the first to sample food and had higher bite rates than subordinates, including when foraging for microplastics. Importantly, how dominance affected foraging behavior depended on group size and on whether groups were presented with familiar or novel foods. Furthermore, individuals were consistent in their foraging behavior across trials with different group sizes, indicating the formation of stable social roles. These results suggest that predicting the ecological and evolutionary consequences of evolutionary traps will require an understanding of how social structures influence trap susceptibility.

A central goal of ecosystem restoration is to promote diverse, native-dominated plant communities. However, restoration outcomes can be highly variable. One cause of this variation may be the decisions made during the seed mix design process, such as choosing the number of species to include (sown diversity) or the number of locations each species should be sourced from (source diversity, manipulated to affect genetic diversity). The effects that seed mixes have on plant communities may be further modified by other factors at the restoration site, including edge proximity and consumer pressure. Few studies have evaluated both these seed mix attributes together, and none have done so while accounting for realistic restoration site attributes. To address this research need, we conducted a prairie restoration experiment where two aspects of seed mix design (sown diversity and source diversity) and two restoration site factors (edge proximity and vertebrate granivore/herbivore consumer access) were manipulated across 12 replicate fields. We found that when seed mix design impacted plant community structure, these effects were dependent on consumer access or edge proximity and were more prominent after one versus five growing seasons. Low seed source diversity plots had more sown species than high source diversity ones, but only when consumers had access. Similarly, low species diversity plots had higher richness and cover of species included in both the low and high species diversity mixes, but this effect weakened over time. Additionally, plots with high species diversity were buffered from the typically detrimental effects of edges and consumers, although this did not always result in greater sown species abundance. Unexpectedly, plots with the most sown species were those sown with either low source diversity or low species diversity seed mixes, perhaps due to lower seeding rates of reliably establishing species. Our results illustrate how the influences of seed mix design on restored plant communities can be highly contingent on factors like edges, consumers, and time.

Pathogens that infect multiple host species have an increased capacity to cause extinctions through parasite-mediated apparent competition. Given unprecedented and continuing losses of biodiversity due to Batrachochytrium dendrobatidis (Bd), the causative fungus of the amphibian skin disease chytridiomycosis, a robust understanding of the mechanisms driving cross-species infection dynamics is essential. Here, we used stage-structured, susceptible-infected compartmental models to explore drivers of Bd-mediated apparent competition between two sympatric amphibians, the critically endangered Litoria spenceri and the non-threatened Litoria lesueurii. We additionally simulated the impact of plausible L. spenceri conservation management interventions on competitive outcomes between these two species. Despite being more susceptible to disease than its competitor, a high relative rate of recruitment allowed the non-threatened L. lesueurii to reach substantially higher densities than L. spenceri in our baseline models, applying a strong absolute force of infection on L. spenceri as an amplifying host. However, simulated management interventions which bolstered L. spenceri recruitment (i.e., captive breeding and release, removal of predatory non-native trout) spurred strong recoveries of L. spenceri while simultaneously (1) increasing the force of Bd infection in the environment and (2) reducing L. lesueurii population density. At high and moderate elevations, combined captive breeding/release and non-native trout removal were sufficient to make L. spenceri the most abundant species. Overall, our results demonstrate the importance of recruitment in moderating pathogen dynamics of multi-host amphibian chytridiomycosis systems. While infection-based parameters are undoubtedly important in Bd management, modifying relative rates of recruitment can substantially alter pathogen-mediated competition between species of an amphibian community.

Subsidy–stress gradients offer a useful framework for understanding ecological responses to perturbation and may help inform ecological metrics in highly modified systems. Historic, region-wide shifts from bottomland hardwood forest to row crop agriculture can cause positively skewed impact gradients in alluvial plain ecoregions, resulting in tolerant organisms that typically exhibit a subsidy response (increased abundance in response to environmental stressors) shifting to a stress response (declining abundance at higher concentrations). As a result, observed biological tolerance in modified ecosystems may differ from less modified regions, creating significant challenges for detecting biological responses to restoration efforts. Using the agriculturally dominated Mississippi Alluvial Plain (MAP) ecoregion in Mississippi, USA, as a case study, we tested the hypothesis that macroinvertebrate taxa that typically display a subsidy response to nutrient enrichment in less modified ecoregions (i.e., nutrient-tolerance) shift to a stress response to increasing nutrients in highly modified watersheds with elevated baseline nutrient conditions (i.e., nutrient intolerance). The abundance and diversity of MAP-specific intolerant taxa identified with threshold indicator taxa analysis were either unresponsive or exhibited a subsidy response to increasing nutrients in less modified ecoregions in Mississippi with less land alteration and lower nutrient concentrations, but declined at higher concentrations, providing evidence for a stress response to elevated nutrients in the MAP. Additionally, MAP-specific tolerant and intolerant taxa richness responded to increased nutrients predictably and consistently across space and time within the MAP. However, in MAP streams, elevated specific conductance was predicted to dampen the response of tolerant and intolerant taxa richness to increasing nutrient concentrations, highlighting the importance of considering multistressor interactions when interpreting biological data. Lastly, we demonstrate the efficacy of this approach with sediment bacterial communities characterized with amplicon sequencing, which lack sufficient life history characteristics necessary for the development of multimetric indices. Both macroinvertebrate and bacterial communities responded similarly to increasing nutrient concentrations, suggesting DNA-based approaches may provide an efficient biological assessment tool for monitoring water quality improvements in highly modified watersheds.

Fire shapes biodiversity in many forested ecosystems, but historical management practices and anthropogenic climate change have led to larger, more severe fires that threaten many animal species where such disturbances do not occur naturally. As predators, owls can play important ecological roles in biological communities, but how changing fire regimes affect individual species and species assemblages is largely unknown. Here, we examined the impact of fire severity, history, and configuration over the past 35 years on an assemblage of six forest owl species in the Sierra Nevada, California, using ecosystem-scale passive acoustic monitoring. While the negative impacts of fire on this assemblage appeared to be ephemeral (1–4 years in duration), spotted owls avoided sites burned at high-severity for up to two decades after a fire. Low- to moderate-severity fire benefited small cavity-nesting species and great horned owls. Most forest owl species in this study appeared adapted to fire within the region's natural range of variation, characterized by higher proportions of low- to moderate-severity fire and relatively less high-severity fire. While some species in this assemblage may be more resilient to severe wildfire than others, novel “megafires” that are larger, more frequent, and contiguously severe may limit the distribution of this assemblage by reducing the prevalence of low- to moderate-severity fire and eliminating habitat for a closed-canopy species for multiple decades. Management strategies that restore historical low- to moderate-severity fire with small patches of high-severity fire and promote a mosaic of forest conditions will likely facilitate the conservation of this assemblage of forest predators.

Human-caused conversion of natural habitat areas to developed land cover represents a major driver of habitat loss and fragmentation, leading to reorganization of biological communities. Although protected areas and urban greenspaces can preserve natural systems in fragmented landscapes, their efficacy has been stymied by the complexity and scale-dependency underlying biological communities. While migratory bird communities are easy to-study and particularly responsive to anthropogenic habitat alterations, prior studies have documented substantial variation in habitat sensitivity across species and migratory groups. This may make approaches that explicitly consider the hierarchical nature of ecological organization useful for planning and decision-making, particularly in developed landscapes. Herein, we leverage regional vegetation and breeding bird monitoring efforts to investigate the influences of spatial scale, urbanization, and migratory habit on breeding bird occupancy across Cleveland Metroparks, a large urban park system in Ohio. Using multispecies occupancy models, we found that fine-scale vegetation covariates were more predictive of bird community dynamics than landscape-level covariates, suggesting positive benefits of vegetation management activities for breeding bird communities. We also found that short-distance migrants were positively associated with plants that have broad ecological tolerances and that tropical migrants were more negatively associated with human development than other migratory groups. While local vegetation management may be effective for protecting sensitive breeding bird communities, many tropical migrants required intact forests with low human development and may require targeted habitat management for continued breeding-season occupancy. More broadly, this study emphasizes how avian management strategies in developed landscapes should consider features at multiple spatial scales—as well as species-specific migratory behaviors.

Livestock grazing and trampling have been shown to reduce arthropod populations. Among arthropods, defoliating lepidopterans are particularly important for their impact on trees, the keystone structures of agroforestry systems. This study investigates the impact of livestock on the community of defoliating lepidopterans in agroforestry systems. We conducted both experimental and observational studies in the mid-west and western regions of the Iberian Peninsula. In our field experiment, we sampled lepidopteran caterpillars in areas with livestock and in areas where livestock had been excluded for short and long periods. To validate our experimental results, we conducted a field survey across seven areas with and without livestock in the western Iberian Peninsula. Our findings revealed that after 2 years from the start of the experiment, the exclusion of livestock led to an increase in the abundance and species richness of lepidopterans, as well as shifts in their community composition. Our experimental findings were corroborated by our field survey. Interestingly, we found that the differences in community composition among exclusions were primarily due to species nestedness. Livestock exclusion consistently favored species that pupate in the ground, suggesting that livestock can alter the lepidopteran community by predating or accidentally trampling these species. This study underscores the significant role livestock play in modifying the community of defoliating lepidopterans in Mediterranean agroforestry systems (oak savannahs), with important implications for food webs and species interactions.

Plant vendors generate a commercial species pool, the subset of species in a regional flora that is purchasable. The availability of plant species from commercial vendors can influence the composition and outcomes of conservation, landscaping, and restoration plantings. Although previous research suggests that most plant species are unavailable, there is little information that identifies the plant characteristics associated with commercial availability. We studied the composition of the commercial species pool by examining the ecology, phylogeny, and phenology of a regional flora in the Midwestern United States. We used a database of native plant species sold by 557 vendors throughout the Midwest (USA) to characterize species' availability. We compiled ecological characteristics of all plant species, including range size, growth form, moisture requirements, and conservatism—meaning fidelity to high-quality natural areas. We characterized phenological (bloom time) data for a subset of the regional flora. Finally, we constructed a regional phylogeny to assess the phylogenetic signal of plant availability. We expected that commercially unavailable species would be niche specialists or short-lived (often nonconservative “weedy”) species, and that they would bloom earlier in the season and for a shorter time. We found that commercially available species were more long-lived, had larger range sizes, had intermediate fidelities to wetlands and high-quality or disturbed natural areas, and were associated with certain plant types, especially shrubs and trees. In contrast, ferns and graminoids were underrepresented in the commercial trade. There was a strong phylogenetic signal associated with commercial availability; some plant families had nearly all or none of their species commercially available. Example families with low representation included Orchidaceae, Potamogetonaceae, Cyperaceae, and fern families. Longer bloomed species were more commercially available, but we did not find differences in availability between early- and late-blooming species. Despite the diversity of the commercial pool in the Midwest, it is an unrepresentative, nonrandom subset of the regional species pool. This finding may promote the mismatch in species diversity and composition between remnant natural habitats and restorations because many specialized species are commercially unavailable to conservation and restoration practitioners. We encourage strategies to promote the availability of underrepresented plant diversity in the commercial species pool.

Although agriculture and plantation forestry have decreased natural open habitats and old-growth forests, conservation in managed lands is considered essential for achieving “nature-positive” goals that reverse biodiversity trends from negative to positive. From subboreal to temperate regions, mature conifer plantations with broadleaved trees (BLTs) offer suitable habitats for species preferring mature natural BLT forests, whereas young plantations harbor species depending on early successional (ES) habitats. However, the functional forms of stand age and BLT, and their context dependency, remain unknown. We quantified the effects of stand age (3–98 years), BLT proportion (0%–97.5%), and their interaction on ES and BLT bird species in plantations, as well as the dependency of these effects on regional/seasonal climates. For both groups, we also explored whether plantations could be comparable habitats to BLT-dominated natural forests (stand age: 6–134 years) across Hokkaido (78,420 km²), northern Japan. ES bird species' richness and abundance decreased exponentially with stand age in plantations. This pattern was not evident in natural forests although only two ES stands were surveyed due to the rarity of natural forest harvesting. ES plantations in cooler regions showed higher habitat values, reflecting a climate-dependent species composition. No ES species occurred in winter. Both stand age and BLT proportion increased BLT bird species richness and abundance in a concave manner, except for age in stands with few BLTs. The positive effects of BLT were more evident in younger stands with fewer BLTs. Mature plantations with 25% BLTs supported 62% of breeding BLT bird abundance in old natural forests. In winter, lower regional temperatures weakened the positive effects of stand age and strengthened the positive effects of BLT proportion, reflecting temperature-dependent habitat selection across species. Our results suggest that regular plantation harvesting can play a critical role in restoring ES bird species across Hokkaido. To conserve BLT bird species, retaining even small amounts of BLTs within plantations may be more cost-effective than long-rotation plantation forestry or only protecting existing natural old-growth forests. Our study shows that on-site conservation within plantations across regions and seasons, when coupled with nature reserve management, can contribute to restoring biodiversity.