Ecological Applications最新文献

Tidal marshes can contribute to nature-based shoreline protection by reducing the wave load onto the shore and reducing the erosion of the sediment bed. To implement such nature-based shoreline erosion protection requires the ability to quickly restore or create highly stable and erosion-resistant tidal marshes at places where they currently do not yet occur. Therefore, we aim to identify the drivers controlling the rate by which sediment stability builds up in young pioneer marshes. Sediment stability proxies were measured over age gradients spanning 18 years in six tidal marsh sites in the Western Scheldt estuary (SW Netherlands): Three were dominated by Spartina anglica, a densely growing pioneer species, and three by Scirpus maritimus, a less densely growing pioneer species. Our results showed that the presence of densely growing Spartina anglica increased sediment shear strength compared to the unvegetated tidal flat, while less densely growing Scirpus maritimus did not. This difference may be related to the contrasting clonal expansion strategies and related root densities of these two pioneer species. Sediment stability did not increase further beyond 6 years of coverage by Spartina anglica, implying that the observed effect of Spartina anglica on sediment stability occurs fast (<6 years). Furthermore, sediment stability often increased with decreasing inundation duration and sediment water content. This study shows that in order to create erosion-resistant sediment beds in future marsh restoration projects, the aim should be to create densely vegetated tidal marshes with well-draining, cohesive sediments at relatively high intertidal elevation. Although the development of erosion resistance takes time, our study demonstrates that in the case of densely growing Spartina anglica marshes, increased sediment bed stability can already be reached after 6 years. The ability of Spartina anglica marshes to increase sediment bed stability within 6 years, in combination with wave attenuation and sediment accretion, offers promising perspectives to implement marsh restoration projects as a nature-based shoreline protection strategy that can start to deliver its protective service within a reasonable amount of time.

Wild solitary bees face a host of challenges from the simplification of landscapes and biodiversity loss to invasive species and urbanization. Pollinator researchers and restoration workers thus far gave much attention to increase flower cover to reduce the impact of these anthropogenic pressures. Over 30% of bee species need nonfloral resources such as leaves and resin for their survival and reproduction. However, the importance of leaves in bee ecology, particularly for leafcutter bees, has received very little attention. Leafcutter bees have global distribution and cut leaves for constructing brood chambers. We have very little information for (a) what bees use and do not use for foraging leaves and (b) what leaf and plant traits and plant community traits drive plant preference and plant usage. To fill this gap and recommend plants for leafcutter bee conservation, we examined 13,062 plants of 612 species and 107 families distributed in 165 plant communities of nine towns/cities of four south Indian states. The plant community of nine locations and four states was quite dissimilar, but had similar proportion of native and exotic plants. The probability of a plant foraged for leaf is governed by its clade, family, nativity, and leaf dimension, particularly the leaf width. Bees have a clear preference for plants of common families, such as Fabaceae, Phyllanthaceae, and Meliaceae for foraging leaves, but bees going to plants of distant lineages, including rare species and families is not rare. At the same time, bees also avoided plants of several cosmopolitan families, such as Apocynaceae, Moraceae, Sapotaceae, and Asteraceae, among others. Bees preferred exotic plants more to native plants. The plant usage in communities is predicted by species richness, proportion of Fabaceae plants in communities, and proportion of herbs; plant diversity and abundance are not crucial drivers. Our study suggests that the bees' preference for leaf-foraging plants is not random, but governed by leaf, plant, and plant community traits. The preference for exotic plants is helpful for planning urban and homestead greening projects as they are dominated by exotics.

Large-scale restoration projects are an exciting and often untapped opportunity to use an experimental approach to inform ecosystem management and test ecological theory. In our $10M tidal marsh restoration project, we installed over 17,000 high marsh plants to increase cover and diversity, using these plantings in a large-scale experiment to test the benefits of clustering and soil amendments across a stress gradient. Clustered plantings have the potential to outperform widely spaced ones if plants alter conditions in ways that decrease stress for close neighbors. Here, we test whether intraspecific facilitation improves restoration outcomes using a suite of seven high marsh species native to central California salt marshes. We also applied a biochar treatment to test whether soil amendment boosts restoration success. We compared the performance of clustered and uniform plantings across the high marsh elevation gradient for 3 years. There was a strong effect of elevation on plant performance and clear signs of plant stress related to soil conditions. Clustering slightly improved the survival of one species out of seven, although clustering did not benefit that species in a follow-up experiment under more stressful conditions. By contrast, clustering had strong negative effects on the growth and/or cover of all species tested. The stressors in this system—likely related to compaction and soil salinity—were not mitigated by neighbors or biochar. The prevailing negative effect on seven species from distinct evolutionary lineages lends strong generality to our findings. We therefore conclude that for this and similar high marsh systems, intraspecific facilitation confers no benefits and practitioners should space plants widely to minimize competition. To take full advantage of the learning opportunities provided by large-scale restoration projects, we recommend including experimental treatments and monitoring the response of multiple species across years to refine best practices and inform adaptive management.

Grassland restoration is an important conservation intervention supporting declining insect pollinators in threatened calcareous grassland landscapes. While the success of restoration is often quantified using simple measures of diversity or similarity to target communities, these measures do not capture all fundamental aspects of community reconstruction. Here, we develop species–habitat networks that aim to define habitat-level foraging dependencies of pollinators across restored grassland landscapes and compare their value to these more conventional measures of community restoration. We assessed this across Salisbury Plain (UK), which represents the largest area of chalk grassland in northwestern Europe, encompassing six distinct management types aimed at the restoration and maintenance of species-rich calcareous grassland. Sites that were previously disturbed or reverting from arable agriculture were comparable with those of ancient grasslands in terms of pollinator abundance and species richness. However, intensively managed grasslands exhibited notably lower values across nearly all measured indicators, including flower and pollinator richness and abundance, than ancient grasslands, with unmanaged grasslands following closely behind. This underscores the need for caution with both long-term neglect and highly intensive management. Applying our species–habitat network approach, we found that pollinator communities in grasslands recovering from past military disturbance showed stronger modular associations with those in ancient grasslands than areas recovering from intensive agriculture. This highlights the importance of habitat history in shaping restoration trajectories. We propose that species–habitat networks should be part of the standard analytical toolkit assessing the effectiveness of restoration at landscape scale, particularly for mobile species such as insects.

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.