Compositional and functional stability of arthropod communities in the face of ant invasions

There is a general consensus that the diversity of a biotic community can have an influence on its stability, but the strength, ubiquity, and relative importance of this effect is less clear. In the context of biological invasions, diversity has usually been studied in terms of its effect on a community's invasibility, but diversity may also influence stability by affecting the magnitude of compositional or functional changes experienced by a community upon invasion. We examined the impacts of invasive ants on arthropod communities at five natural area sites in the Hawaiian Islands, and assessed whether differences among sites in community diversity and density variables were related to measures of stability. Ant invasion was usually associated with significant changes in overall community composition, as measured by Bray-Curtis distances, particularly among endemic subsets of the communities. Changes in mean species richness were also strong at three of the five sites. Among sites, diversity was negatively related to stability as measured by resistance to overall compositional change, but this effect could not be separated from the strong negative effect of invasive ant density on compositional stability. When compositional stability was measured as proportional change in richness, the best predictor of stability among endemic community subsets was endemic richness, with richer communities losing proportionately more species than species-poor communities. This effect was highly significant even after controlling for differences in invasive ant density and suggested that communities that had already lost many endemic species were resistant to further species loss upon ant invasion, while more intact communities remained vulnerable to species loss. Communities underwent strong but idiosyncratic functional shifts in association with ant invasion, both in terms of trophic structure and total arthropod biomass. There were no apparent relationships, however, between functional stability and community diversity or density measures. Instead, invasive ant density was the best among-site predictor of the magnitude of functional change. Overall, diversity appeared to be a poor predictor of stability in the face of ant invasion in these communities, possibly because any actual diversity effects were overshadowed by community-specific factors and variation in the magnitude of the ant-mediated perturbation.     

A process-based population dynamics model to explore target and non-target impacts of a biological control agent

The risks and benefits associated with efforts to control invasive alien species using classical biological control are being subjected to increasing scrutiny. A process-based population dynamics model was developed to explore the interactions between a folivorous biological control agent, Cleopus japonicus, and its plant host Buddleja davidii. The model revealed that climate could have a significant impact upon the interactions between B. davidii and C. japonicus. At the coolest sites, the impact of C. japonicus on B. davidii was slowed, but it was still eventually capable of controlling populations of B. davidii. At the warmer sites where both B. davidii and C. japonicus grew faster, B. davidii succumbed rapidly to weevil damage. We hypothesise that barring an encounter with a natural enemy, C. japonicus will eventually be able to provide sustained control B. davidii throughout the North Island of New Zealand. The model scenarios illustrate the potential for the C. japonicus population to attain high densities rapidly, and to defoliate patches of B. davidii, creating the potential for spill-over feeding on non-target plants. The potential magnitude of this threat will depend partly on the climate suitability for C. japonicus, the pattern by which it migrates in response to a reduction in the available leaf resource, and the suitability of non-target plants as hosts. In all migration scenarios considered, the pattern of population growth and resource consumption by C. japonicus was exponential, with a strong tendency toward complete utilisation of resource patches more quickly at the warmer compared to colder sites. In addition to providing some useful hypotheses about the effects of climate on the biological control system, and the non-target risks, it also provides some insight into the mechanisms by which climate affects the system.     

Influence of Landscape Elements in Riparian Buffers on the Conservation of Semiaquatic Amphibians

Abstract:  Studies on riparian buffers have usually focused on the amount of land needed as habitat for the terrestrial life stages of semiaquatic species. Nevertheless, the landscape surrounding wetlands is also important for other key processes, such as dispersal and the dynamics of metapopulations. Multiple elements that influence these processes should therefore be considered in the delineation of buffers. We analyzed landscape elements (forest cover, density of roads, and hydrographic network) in concentric buffers to evaluate the scale at which they influence stream amphibians in 77 distinct landscapes. To evaluate whether our results could be generalized to other contexts, we determined whether they were consistent across the study areas. Amphibians required buffers of 100–400 m of suitable terrestrial habitat, but interspecific differences in the amount of habitat were large. The presence of amphibians was related to roads and the hydrographic network at larger spatial scales (300–1500 m), which suggests that wider buffers are needed with these elements. This pattern probably arose because these elements influence dispersal and metapopulation persistence, processes that occur at large spatial scales. Furthermore, in some cases, analyses performed on different sets of landscapes provided different results, which suggests caution should be used when conservation recommendations are applied to disparate areas. Establishment of riparian buffers should not be focused only on riparian habitat, but should take a landscape perspective because semiaquatic species use multiple elements for different functions. This approach can be complex because different landscape elements require different spatial extents. Nevertheless, a shift of attention toward the management of different elements at multiple spatial scales is necessary for the long-term persistence of populations.     

Increased primary production shifts the structure and composition of a terrestrial arthropod community

Numerous studies have examined relationships between primary production and biodiversity at higher trophic levels. However, altered production in plant communities is often tightly linked with concomitant shifts in diversity and composition, and most studies have not disentangled the direct effects of production on consumers. Furthermore, when studies do examine the effects of plant production on animals in terrestrial systems, they are primarily confined to a subset of taxonomic or functional groups instead of investigating the responses of the entire community. Using natural monocultures of the salt marsh cordgrass Spartina alterniflora, we were able to examine the impacts of increased plant production, independent of changes in plant composition and/or diversity, on the trophic structure, composition, and diversity of the entire arthropod community. If arthropod species richness increased with greater plant production, we predicted that it would be driven by: (1) an increase in the number of rare species, and/or (2) an increase in arthropod abundance. Our results largely supported our predictions: species richness of herbivores, detritivores, predators, and parasitoids increased monotonically with increasing levels of plant production, and the diversity of rare species also increased with plant production. However, rare species that accounted for this difference were predators, parasitoids, and detritivores, not herbivores. Herbivore species richness could be simply explained by the relationship between abundance and diversity. Using nonmetric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM), we also found significant changes in arthropod species composition with increasing levels of production. Our findings have important implications in the intertidal salt marsh, where human activities have increased nitrogen runoff into the marsh, and demonstrate that such nitrogen inputs cascade to affect community structure, diversity, and abundance in higher trophic levels.     

Lake to land subsidies: experimental addition of aquatic insects increases terrestrial arthropod densities

Aquatic insects are a common and important subsidy to terrestrial systems, yet little is known about how these inputs affect terrestrial food webs, especially around lakes. Myvatn, a lake in northern Iceland, has extraordinary midge (Chironomidae) emergences that result in large inputs of biomass and nutrients to terrestrial arthropod communities. We simulated this lake-to-land resource pulse by collecting midges from Myvatn and spreading their dried carcasses on 1-m2 plots at a nearby site that receives very little midge deposition. We hypothesized a positive bottom-up response of detritivores that would be transmitted to their predators and would persist into the following year. We sampled the arthropod community once per month for two consecutive summers. Midge addition resulted in significantly different arthropod communities and increased densities of some taxa in both years. Detritivores, specifically Diptera larvae, Collembola, and Acari increased in midge-addition plots, and so did some predators and parasitoids. Arthropod densities were still elevated a year after midge addition, and two years of midge addition further increased the density of higher-order consumers (e.g., Coleoptera and Hymenoptera). Midge addition increased arthropod biomass by 68% after one year and 108% after two years. By manipulating the nutrient pulse delivered by midges we were able to elucidate food web consequences of midge deposition and spatial and temporal dynamics that are difficult to determine based on comparative approaches alone. Resources cross ecosystem boundaries and are assimilated over time because of life-history strategies that connect aquatic and terrestrial food webs and these systems cannot be fully understood in isolation from each other.     

Effects of Drainage‐Basin Geomorphology on Insectivorous Bird Abundance in Temperate Forests

Abstract: Interfaces between terrestrial and stream ecosystems often enhance species diversity and population abundance of ecological communities beyond levels that would be expected separately from both the ecosystems. Nevertheless, no study has examined how stream configuration within a watershed influences the population of terrestrial predators at the drainage‐basin scale. We examined the habitat and abundance relationships of forest insectivorous birds in eight drainage basins in a cool temperate forest of Japan during spring and summer. Each basin has different drainage‐basin geomorphology, such as the density and frequency of stream channels. In spring, when terrestrial arthropod prey biomass is limited, insectivorous birds aggregated in habitats closer to streams, where emerging aquatic prey was abundant. Nevertheless, birds ceased to aggregate around streams in summer because terrestrial prey became plentiful. Watershed‐scale analyses showed that drainage basins with longer stream channels per unit area sustained higher densities of insectivorous birds. Moreover, such effects of streams on birds continued from spring through summer, even though birds dispersed out of riparian areas in the summer. Although our data are from only a single year, our findings imply that physical modifications of stream channels may reduce populations of forest birds; thus, they emphasize the importance of landscape‐based management approaches that consider both stream and forest ecosystems for watershed biodiversity conservation.     

农药对陆生生物的生态毒性及风险评估

农药的使用会对非靶标生物造成影响,由此世界各国都采取了风险控制手段以预防农药造成的生态危害。本文综述了欧洲、美国和日本针对农药开展的陆生生态系统风险评估方法,包括陆生非靶标生物、风险评估模型、风险评估的基本方法及生态毒性的评价指标。同时分析了农药登记管理对陆生生生物的生态毒性及风险评估中存在的科学问题,且提出了方法学的发展方向。     

Simulation of herbicide impacts on a plant community: comparing model predictions of the plant community model IBC-grass to empirical data

Background

Semi-natural plant communities such as field boundaries play an important ecological role in agricultural landscapes, e.g., provision of refuge for plant and other species, food web support or habitat connectivity. To prevent undesired effects of herbicide applications on these communities and their structure, the registration and application are regulated by risk assessment schemes in many industrialized countries. Standardized individual-level greenhouse experiments are conducted on a selection of crop and wild plant species to characterize the effects of herbicide loads potentially reaching off-field areas on non-target plants. Uncertainties regarding the protectiveness of such approaches to risk assessment might be addressed by assessment factors that are often under discussion. As an alternative approach, plant community models can be used to predict potential effects on plant communities of interest based on extrapolation of the individual-level effects measured in the standardized greenhouse experiments. In this study, we analyzed the reliability and adequacy of the plant community model IBC-grass (individual-based plant community model for grasslands) by comparing model predictions with empirically measured effects at the plant community level.

Results

We showed that the effects predicted by the model IBC-grass were in accordance with the empirical data. Based on the species-specific dose responses (calculated from empirical effects in monocultures measured 4 weeks after application), the model was able to realistically predict short-term herbicide impacts on communities when compared to empirical data.

Conclusion

The results presented in this study demonstrate an approach how the current standard greenhouse experiments—measuring herbicide impacts on individual-level—can be coupled with the model IBC-grass to estimate effects on plant community level. In this way, it can be used as a tool in ecological risk assessment.

     

Plant genes link forests and streams

Although it is understood that the composition of riparian trees can affect stream function through leaf litter fall, the potential effects of genetic variation within species are less understood. Using a naturally hybridizing cottonwood system, we examined the hypothesis that genetic differences among two parental species (Populus fremontii and P. angustifolia) and two groups of their hybrids (F1 and backcrosses to P. angustifolia) would affect litter decomposition rates and the composition of the aquatic invertebrate community that colonizes leaves. Three major findings emerged: (1) parental and hybrid types differ in litter quality, (2) decomposition differs between two groups, a fast group (P. fremontii and F1 hybrid), and a slow group (P. angustifolia and backcross hybrids), and (3) aquatic invertebrate communities colonizing P. fremontii litter differed significantly in composition from all other cross types, even though P. fremontii and the F1 hybrid decomposed at similar rates. These findings are in agreement with terrestrial arthropod studies in the same cottonwood system. However, the effects are less pronounced aquatically than those observed in the adjacent terrestrial community, which supports a genetic diffusion hypothesis. Importantly, these findings argue that genetic interactions link terrestrial and aquatic communities and may have significant evolutionary and conservation implications.     

Shrubsteppe Bird Response to Habitat and Landscape Variables in Eastern Washington, U.S.A.

Abstract: The landscape of the intermountain west has changed dramatically in the last 150 years, particularly in the state of Washington, where over half the native shrubsteppe ecosystem has been converted to agricultural lands, resulting in a fragmented landscape with few extensive tracts of shrubsteppe. We examined the historical and current distribution of shrubsteppe on different soil types in eastern Washington, and we censused bird communities at 78 sites in shrubsteppe from 1991 to 1993. We compared abundance of species among soil types and range conditions and developed models of species occurrence using site-specific vegetation and landscape variables. The pattern of shrubsteppe conversion has resulted in a disproportionate loss of deep soil communities. Eight bird species showed strong relationships with soil type and three with range condition. These associations likely resulted from the influence of soil type and range history on the vegetation of these communities. Brewer's Sparrows (  Spizella breweri ) and Sage Sparrows ( Amphispiza belli ) reached their highest abundances in deep, loamy soils, whereas Loggerhead Shrikes (   Lanius ludovicianus ) were most abundant in deep, sandy soils. Sage Sparrows occurred more frequently in landscapes dominated by shrubsteppe, indicating a negative relationship with fragmentation. Our results suggest that fragmentation of shrubsteppe and the pattern of agricultural conversion among soil types have had detrimental effects on numerous shrubsteppe species. The landscape for species with an affinity for deep, loamy soil communities has changed considerably more than the overall loss of shrubsteppe would indicate. Conservation practices that emphasize retention of shrubsteppe communities on deep soils and that reduce further fragmentation will be critical to the maintenance of avian biological diversity in this system.     

Schnecken unter Stress

Background In ecophysiology and ecotoxicology, gastropods are important both as target organisms for molluscicides and non-target organisms for environmental pollutants or other environmental stressors. With respect to both aspects, biomarkers are investigated at different levels of biological organization in order to understand mechanisms which enable gastropods to cope with or even to benefit from unfavourable environmental conditions. Main topics The paper focuses on the ecotoxicological and ecophysiological work of the author on gastropods which will be reviewed in the context of the state of knowledge in this field of research. In addition to cellular aspects in biomarker research, also biochemical responses of snails to environmental stress (stress proteins, metallothioneins, and metabolic enzymes) will be addressed. Conclusions The paper highlights the suitability of terrestrial and aquatic gastropods as sensitive indicators of environmental stress induced by chemicals or other non-chemical factors. Biomarker studies have been shown not only to be applicable in environmental risk assessment but also to provide fundamental and background knowledge necessary to understand correlations of responses at different levels of biological organization. Recommendations and perspectives A standardized toxicity test with the grapevine snail (ISO 15952) has been established for toxicity assessment in terrestrial habitats. However, freshwater gastropods display a high sensitivity as well, e.?g. to endocrine disrupters, and should be incorporated into future standardized assays for aquatic toxicity testing on the basis of existing knowledge.     

Changes in Arthropod Assemblages along a Wide Gradient of Disturbance in Gabon

Abstract: Searching for indicator taxa representative of diverse assemblages, such as arthropods, is an important objective of many conservation studies. We evaluated the impacts of a wide gradient of disturbance in Gabon on a range of arthropod assemblages representing different feeding guilds. We examined 4 × 10⁵ arthropod individuals from which 21 focal taxa were separated into 1534 morphospecies. Replication included the understory of 3 sites in each of 4 different stages of forest succession and land use (i.e., habitats) after logging (old and young forests, savanna, and gardens). We used 3 complementary sampling methods to survey sites throughout the year. Overall differences in arthropod abundance and diversity were greatest between forest and open habitats, and cleared forest invaded by savanna had the lowest abundance and diversity. The magnitude of faunal differences was much smaller between old and young forests. When considered at this local scale, anthropogenic modification of habitats did not result in a monotonous decline of diversity because many herbivore pests and their associated predators and parasitoids were abundant and diverse in gardens, where plant productivity was kept artificially high year‐round through watering and crop rotation. We used a variety of response variables to measure the strength of correlations across survey locations among focal taxa. These could be ranked as follows in terms of decreasing number of significant correlations: species turnover > abundance > observed species richness > estimated species richness > percentage of site‐specific species. The number of significant correlations was generally low and apparently unrelated to taxonomy or guild structure. Our results emphasize the value of reporting species turnover in conservation studies, as opposed to simply measuring species richness, and that the search for indicator taxa is elusive in the tropics. One promising alternative might be to consider “predictor sets” of a small number of taxa representative of different functional groups, as identified in our study.     

Habitat and landscape characteristics underlying anuran community structure along an urban-rural gradient

Urbanization has been cited as an important factor in worldwide amphibian declines, and although recent work has illustrated the important influence of broad-scale ecological patterns and processes on amphibian populations, little is known about the factors structuring amphibian communities in urban landscapes. We therefore examined amphibian community responses to wetland habitat availability and landscape characteristics along an urban-rural gradient in central Iowa, USA, a region experiencing rapid suburban growth. We conducted call surveys at 61 wetlands to estimate anuran calling activity, and quantified wetland habitat structure and landscape context. We used canonical correspondence analysis (CCA) to examine patterns in anuran community structure and identify the most important variables associated with those patterns. Urban density at the landscape scale had a significant negative influence on overall anuran abundance and diversity. While every species exhibited a decrease in abundance with increasing urban density, this pattern was especially pronounced for species requiring post-breeding upland habitats. Anurans most affected by urbanization were those associated with short hydroperiods, early breeding activity, and substantial upland habitat use. We suggest that broad-scale landscape fragmentation is an important factor underlying anuran community structure in this region, possibly due to limitations on the accessibility of otherwise suitable habitat in fragmented urban landscapes. This study underscores the importance of a regional approach to amphibian conservation in urban and urbanizing areas; in fragmented landscapes, a network of interconnected wetland and upland habitats may be more likely to support a successful, diverse anuran community than will isolated sites.     

Biozönotisches Testverfahren (PICT-Konzept)

Goal and Scope

A community test is introduced usingin situ periphyton communities and the pollution induced community tolerance for ecotoxicological testing. It was the aim of the study to evaluate the feasibility of the test for the assessment of xenobiotics and contaminated environmental aquatic samples.

Methods

The herbicides Isoproturon and Prometryn were tested using standardised microphytobenthic communities of differing contamination. A pulse-amplitude-modulated fluorescence based method was used to detect the impact of the herbicides on the photosynthetic system of the microalgae.

Results and Conclusions

Despite the variability of the ecosystem (samples were taken from different sites and varying taxonomy throughout a period of two months), the tests show high sensitivity and good reproduction features. EC₅₀ values of 0.025 mg L^?1 for Isoproturon and 0.016 mg L^?1 for Prometryn were evaluated. These effect concentrations ranged in the same order of magnitude as the results derived from cell reproduction inhibition tests withScenedesmus vacuolatus (0.029 mg L^?1 for Isoproturon and 0.012 mg L^?1 for Prometryn). For Isoproturon, the test was able to differentiate effect concentrations for single algal classes within natural communities. The test was used to assess a contaminated effluent entering a stream (Spittelwasser) in the region of Bitterfeld. The effluent originate from a local chemical industry site, where Prometryn was produced for 4 decades. According to the PICT-concept (pollution induced community tolerance), we hypothesed that periphyton taken downstream of the effluent was more tolerant to Prometryn than uncontaminated communities. It could be shown that the herbicide caused a shift in the concentration response relationships of communities from different contaminated sites, indicating the development of tolerance. We conclude that the test using periphyton communities and considering the development of tolerance is able to evaluate a causal analysis of chronic effects of pollutants on community level. The multi-species test usingin situ communities reflects a higher biological organisation level than a single species laboratory test.

Outlook

The PICT-concept could be used for ecological risk assessment of pollutants in the environment bridging the gap between single species laboratory testing and time consuming mesocosmos and field studies.     

Effects of Invasive Plants on Arthropods

Non‐native plants have invaded nearly all ecosystems and represent a major component of global ecological change. Plant invasions frequently change the composition and structure of vegetation communities, which can alter animal communities and ecosystem processes. We reviewed 87 articles published in the peer‐reviewed literature to evaluate responses of arthropod communities and functional groups to non‐native invasive plants. Total abundance of arthropods decreased in 62% of studies and increased in 15%. Taxonomic richness decreased in 48% of studies and increased in 13%. Herbivorous arthropods decreased in response to plant invasions in 48% of studies and increased in 17%, likely due to direct effects of decreased plant diversity. Predaceous arthropods decreased in response to invasive plants in 44% of studies, which may reflect indirect effects due to reductions in prey. Twenty‐two percent of studies documented increases in predators, which may reflect changes in vegetation structure that improved mobility, survival, or web‐building for these species. Detritivores increased in 67% of studies, likely in response to increased litter and decaying vegetation; no studies documented decreased abundance in this functional group. Although many researchers have examined effects of plant invasions on arthropods, sizeable information gaps remain, specifically regarding how invasive plants influence habitat and dietary requirements. Beyond this, the ability to predict changes in arthropod populations and communities associated with plant invasions could be improved by adopting a more functional and mechanistic approach. Understanding responses of arthropods to invasive plants will critically inform conservation of virtually all biodiversity and ecological processes because so many organisms depend on arthropods as prey or for their functional roles, including pollination, seed dispersal, and decomposition. Given their short generation times and ability to respond rapidly to ecological change, arthropods may be ideal targets for restoration and conservation activities. Efectos de las Plantas Invasoras sobre los Artrópodos     

Effects of river otter activity on terrestrial plants in trophically altered Yellowstone Lake

Animals that deposit aquatically derived nutrients on terrestrial landscapes link food webs and affect a variety of in situ processes. This phenomenon, however, is poorly documented in freshwater habitats, especially where species introductions have drastically changed an ecosystem's trophic structure. In this study, we used stable isotopes to document water-to-land nutrient transport by river otters (Lontra canadensis) around Yellowstone Lake, an ecosystem recently altered by nonnative species invasions. We then investigated the effects of otter fertilization on plant growth and prevalence at latrine (scent-marking) sites and evaluated how the recent changes to the lake's food web could influence these plant responses. Values of delta15N were higher on latrines compared to non-latrine sites in five of seven sample plant taxa. Additionally, latrine grasses had higher percentage N than those from non-latrines. Foliar delta15N positively related to fecal deposition rate for some plants, indicating that increased otter scent-marking led to a rise in these N values. Logistic regression models indicated that otters selected for well-shaded latrines with access to foraging. Atypical latrines, misclassified as non-latrines by the regression models, had values of delta15N similar to correctly classified latrines, suggesting that site effects alone cannot explain elevated N values at otter latrine sites. No difference in plant diversity or percent cover of N-fixing taxa occurred between latrine and nonlatrine sites, though specific genera did differ between site types. Measurements of shoot lengths indicated increased growth of some latrine currants (Ribes sp.). In Yellowstone Lake, a twofold reduction in otter numbers could result in an even greater decline in nutrient deposition at latrines, as otters may become less social in a system with decreased prey availability. Our results highlight the role of animals in linking aquatic and terrestrial habitats in inland freshwater systems and suggest that ongoing changes in the trophic structure of Yellowstone Lake could have unexpected ramifications well beyond the lake itself.     

Comparing community structure on shells of the abalone Haliotis midae and adjacent rock: implications for biodiversity

This paper concerns the effects on biodiversity of depletion of the South African abalone Haliotis midae, which is a long-lived species with a large corrugated shell that provides a habitat for diverse benthic organisms. We compared community structure on H. midae shells with that on adjacent rock at three sites (Cape Point and Danger Point sites A and B) and at two different times of the year at one of these sites. Shells of H. midae consistently supported communities that were distinctly different from those on rock. In particular, three species of non-geniculate (encrusting) corallines, Titanoderma polycephalum, Mesophyllum engelhartii and Spongites discoideus, were all found either exclusively or predominantly on shells, whereas another non-geniculate coralline, Heydrichia woelkerlingii, occurred almost exclusively on adjacent rock. The primary rocky substratum, however, supported a higher number of species than abalone shells. Possible reasons for the differences between the two substrata include the relative age, microtopography and hardness of the substrata; the abundance of grazers on them; and the relative age of different zones of the abalone shell, which support communities at different stages of succession. Diversity on shells was lowest in zones that were either very young or very old, in keeping with the intermediate disturbance hypothesis. The distinctiveness of shell epibiota will increase β diversity despite having a lower α diversity than that of adjacent rock. Decimation of H. midae by overfishing therefore has implications for biodiversity conservation.     

A genetic basis to community repeatability and stability

Recent studies have shown that genetically based traits of plants can structure associated arthropod and microbial communities, but whether the effects are consistent and repeatable across years is unknown. If communities are both heritable (i.e., related individuals tend to support similar communities) and repeatable (i.e., the same patterns observed over multiple years), then plant genetics may also affect community properties previously thought to be emergent, such as "stability." Using replicated clones of narrowleaf cottonwood (Populus angustifolia) and examining an arthropod community of 103 species, we found that (1) individual tree genotypes supported significantly different arthropod communities, which exhibited broad-sense heritability; (2) these findings were highly repeatable over three consecutive years (repeatability = 0.91) indicating that community responses to individual tree genotypes are consistent from year to year; (3) differences among tree genotypes in community stability (i.e., changes in community composition over multiple years) exhibited broad-sense heritability (H(C)2 = 0.32). In combination, these findings suggest that an emergent property such as stability can be genetically based and thus subject to natural selection.     

The effects of habitat loss, fragmentation, and community homogenization on resilience in estuaries.

When changes in the frequency and extent of disturbance outstrip the recovery potential of resident communities, the selective removal of species contributes to habitat loss and fragmentation across landscapes. The degree to which habitat change is likely to influence community resilience will depend on metacommunity structure and connectivity. Thus ecological connectivity is central to understanding the potential for cumulative effects to impact upon diversity. The importance of these issues to coastal marine communities, where the prevailing concept of open communities composed of highly dispersive species is being challenged, indicates that these systems may be more sensitive to cumulative impacts than previously thought. We conducted a disturbance-recovery experiment across gradients of community type and environmental conditions to assess the roles of ecological connectivity and regional variations in community structure on the recovery of species richness, total abundance, and community composition in Mahurangi Harbour, New Zealand. After 394 days, significant differences in recovery between sites were apparent. Statistical models explaining a high proportion of the variability (R2 > 0.92) suggested that community recovery rates were controlled by a combination of physical and ecological features operating across spatial scales, affecting successional processes. The dynamic and complex interplay of ecological and environmental processes we observed driving patch recovery across the estuarine landscape are integral to recovery from disturbances in heterogeneous environments. This link between succession/recovery, disturbance, and heterogeneity confirms the utility of disturbance-recovery experiments as assays for cumulative change due to fragmentation and habitat change in estuaries.     

Impact of Native Plants on Bird and Butterfly Biodiversity in Suburban Landscapes

Abstract:  Managed landscapes in which non-native ornamental plants are favored over native vegetation now dominate the United States, particularly east of the Mississippi River. We measured how landscaping with native plants affects the avian and lepidopteran communities on 6 pairs of suburban properties in southeastern Pennsylvania. One property in each pair was landscaped entirely with native plants and the other exhibited a more conventional suburban mixture of plants—a native canopy with non-native groundcover and shrubs. Vegetation sampling confirmed that total plant cover and plant diversity did not differ between treatments, but non-native plant cover was greater on the conventional sites and native plant cover was greater on the native sites. Several avian (abundance, species richness, biomass, and breeding-bird abundance) and larval lepidopteran (abundance and species richness) community parameters were measured from June 2006 to August 2006. Native properties supported significantly more caterpillars and caterpillar species and significantly greater bird abundance, diversity, species richness, biomass, and breeding pairs of native species. Of particular importance is that bird species of regional conservation concern were 8 times more abundant and significantly more diverse on native properties. In our study area, native landscaping positively influenced the avian and lepidopteran carrying capacity of suburbia and provided a mechanism for reducing biodiversity losses in human-dominated landscapes.