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Trees in a state of decline exhibit a reduced foliage density and accumulate dead branches in their crowns. Consequently, forest decline can markedly affect both the habitats and sources of food for canopy-dwelling insects. The decline-induced increase in canopy openness may also modify the understory, shrub and ground layers, and have cascading effects on associated species. Flight interception traps and green Lindgren traps were used to survey the canopy-dwelling insects in stands of healthy and declining oak trees, in particular two insect orders: Raphidioptera, saproxylic insects associated with canopies, and Mecoptera, necrophagous or opportunistic species associated with the herbaceous or shrub strata. Overall, green Lindgren traps caught more of these insects than fl ight interception traps. The traps caught five species of Raphidioptera. Three of them, Subilla confinis, Phaeostigma major and, to a lesser extent, Phaeostigma notata, were more abundant in stands or plots with declining trees. However, the other two species of Raphidioptera, Atlantoraphidia maculicollis and Xanthostigma xanthostigma exhibited a reverse trend. Two species of Mecoptera, Panorpa germanica and Panorpa communis, were particularly abundant, but unaffected by the level of decline. Our results show that declining forests can either host more or fewer species of Raphidioptera with saproxylic larvae, whereas Mecoptera with ground-living larvae were unaffected. Seasonal phenology and sex ratio of the species are also discussed.

The \"intermediate disturbance hypothesis\" and the \"intermediate productivity hypothesis\" have been widely recognized concepts for explaining patterns of species diversity for the past 40 years. While these hypotheses have generated numerous reviews and meta-analyses, as well as persistent criticism, two prominent papers have recently concluded that both of these hypotheses should be abandoned because of theoretical weaknesses and failure to predict observed diversity patterns. I review these criticisms in the context of the continuing tension between logic and empiricism in the development of ecological theory, and conclude that most of the criticisms are misguided because they fail to recognize the inherent connections between these two hypotheses, and consequently fail to test them appropriately. The logic of every hypothesis is based on the underlying assumptions. In the case of these two hypotheses, the assumptions on which the criticisms of their logic depend are falsified by the strong empirical support for the linked predictions of the hypotheses. This conclusion calls for a reevaluation of the basic assumptions upon which most of ecological competition and diversity theory is based.

Declines in plants and herbivorous insects due to land use abandonment and intensification have been studied in agricultural areas worldwide. We tested four hypotheses, which were complementary rather than mutually exclusive, to understand the mechanisms driving biodiversity declines due to abandonment and intensification. These predict that biodiversity decline is caused by a decline in resource diversity, changes in disturbance regime, surrounding landscape conversion, and a decrease in biomass production. We compared plant richness and butterfly and orthopteran richness and diversity among three land use types in seminatural grasslands: abandoned, traditional, and intensified terraces. Then, we examined effects of changes in resource (plant) richness, frequency of disturbance (mowing), and surrounding landscapes on butterfly and orthopteran diversity to understand the mechanisms driving decline after land abandonment and intensification. Plant and herbivore richness and diversity were significantly lower in abandoned and intensified grasslands than in traditional grasslands. This trend was consistent throughout the seasons in both years of the study. Changes in mowing frequency and surrounding landscape explained plant richness declines as a consequence of land abandonment and intensification. Declines in herbivorous insects were explained by plant richness declines and changes in mowing frequency, but not by landscape changes. Plant and herbivore richness were maximized at an intermediate mowing frequency (approximately twice per year), which is typical practice on traditional terraces. This is the first report demonstrating that the intermediate disturbance hypothesis explained well the biodiversity declines in agricultural ecosystems. The richness and diversity responses of herbivore functional groups to plant richness, mowing frequency, and surrounding landscapes were generally inconsistent with predictions. We found significant trends in which butterfly and orthopteran species with low abundance in traditional terraces were lost in abandoned and/or intensive terraces. This may suggest that the number of individuals of most herbivorous species decreased randomly with respect to life-history traits following a decline in plant richness after changes in disturbance frequency. This study demonstrates that declines in herbivorous insects can be explained by multiple factors, and provides a unified explanation for biodiversity declines in both abandoned and intensified use of agricultural lands, which have often been studied separately.

ContextUrbanization fragments and destroys natural landscapes, generally decreasing bird diversity. While in some cases bird diversity continuously decreases in response to urbanization, in others a non-linear response is evident, with peak bird diversity observed at intermediate levels of urbanization. But many studies previously investigating this pattern are spatially or temporally constrained.ObjectivesIn this study, we analyzed the impacts of urbanization on bird diversity, stratified to native and exotic species. We specifically investigated the differences in bird diversity between natural and urban green areas.MethodsWe used eBird citizen science data (> 4,000,000 bird-survey lists) and remotely-sensed landcover data, throughout the contiguous United States of America.ResultsWe found a non-linear response to urbanization for both species richness and Shannon diversity. There was distinctly greater bird richness and Shannon diversity in urban green areas compared to natural green areas. Our observed response is likely explained by an increase in habitat heterogeneity of urban green areas compared with natural green areas.ConclusionsOur work highlights the importance of diverse urban green areas for supporting bird diversity in urban areas. We recommend that urban planning should focus on maintaining high habitat heterogeneity in urban green areas to promote greater bird diversity.

Disturbance has long been recognized as a critical driver of species diversity in community ecology. Recently, it has been found that the well-known intermediate disturbance hypothesis, which predicts a unimodal diversity—disturbance relationship (DDR), fails to describe numerous experimental observations, as empirical DDRs are diverse. Consequently, the precise form of the DDR remains a topic of debate. Here we develop a simple yet comprehensive metacommunity framework that can account for complex competition patterns. Using both numerical simulations and analytical arguments, we show that strongly multimodal DDRs arise naturally, and this multimodality is quite robust to changing parameters or relaxing the assumption of a strict competitive hierarchy. Having multimodality as a robust property of DDRs in competition models suggests that much of the noise observed in empirical DDRs could be a critical signature of the underlying competitive dynamics.

. Question: How does fire affect the aggregation patterns of trees in a species‐poor oak woodland? Location: East‐central Minnesota, USA. Methods: More than 10 000 trees with DBH > 2 cm (comprising more than 11 000 stems) were monitored in a 16‐ha grid on an annual basis from 1995‐ 2001 in a species‐poor temperate woodland. Different portions of the grid experienced different frequencies of controlled burns. Aggregation indices were calculated for individual species and individual size classes within species. A community‐wide aggregation index was also calculated for different burn units. Spatial data were managed, and many of the aggregation indices calculated using a GIS ArcInfo™ (ESRI). Results: Fire initially increased clumping, although repeated fires reduced it, a finding that suggests a corollary to the intermediate‐disturbance hypothesis, the corollary stating that intermediate levels of disturbance are expected to maximize community‐wide patterns of aggregation. Analyses also showed that all species are aggregated at small scales, that the degree of aggregation of a stem type (species or size) declines with distance from individual stems, that the degree of aggregation of large stems is usually less than that of small stems, and that rare species are more aggregated than common species. Findings from this study are consistent with those from similar studies in other temperate and tropical forests, woodlands, and savannas. Conclusion: The spatial patterns of trees in this woodland are dynamic, continually changing in response to the relative strengths of the often opposing forces of competition, which tends to reduce clumping, and disturbance, which, at low and intermediate frequencies, tends to increase it.

Fire, a frequent disturbance in the Mediterranean, affects pollinator communities. We explored the response of major pollinator guilds to fire severity, across a fire-severity gradient at different spatial scales. We show that the abundance of all pollinator groups responded to fire severity, and that bees and beetles showed in addition a significant species-diversity response. Bees, sawflies, and wasps responded to fire severity at relatively small spatial scales (250–300 m), whereas flies and beetles responded at larger spatial scales. The response of bees, sawflies, and wasps was unimodal, as predicted by the intermediate disturbance hypothesis, whereas flies and beetles showed a negative response. A possible explanation is that the observed patterns (spatial scale and type of response) are driven by taxa-specific ecological and life-history traits, such as nesting preference and body size, as well as the availability of resources in the postfire landscape. Our observational study provides an insight into the effect of fire severity on pollinators. However, future research exploring the explicit link between the pre- and postfire landscape structure and pollinator traits and responses is required for further establishment and understanding of cause–effect relationships.

In this study, we have shown that nutrient input in aquatic ecosystems has different impacts on the various facets of phytoplankton and zooplankton diversity. We designed an experiment with eleven levels of nutrient addition replicated four times. Alpha, beta, and gamma taxonomic and functional diversity indices were calculated based on organisms’ occurrences and abundances in each microcosm, among microcosms of the same treatment and for the set microcosms of a same treatment. There was an increase in species richness and a decrease in equitability along the gradient for both groups. Taxonomic beta diversity based on occurrences was positively related to nutrient gradient, but a hump-shaped relationship between nutrient enrichment and beta diversity was observed when abundance data were considered, showing greater variation in species composition at intermediate levels of nutrient. Alpha functional richness increased for both groups, whereas alpha and gamma RaoQ, and gamma functional divergence decreased, indicating that nutrient enrichment promotes functional trait richness, but also the dominance of species. At small spatial scale and at a short period of time, we showed that taxonomic and functional diversities respond in similar ways to nutrient enrichment. We conclude that nutrient input may modify community composition and affect ecological processes overtime.

Understanding disturbance effects on species diversity and functional diversity is fundamental to conservation planning but remains elusive. We quantified species richness, diversity, and evenness and functional richness, diversity, and evenness of riparian and upland plants along 24 small streams subjected to a range of anthropogenic disturbances in the boreal forest of northwestern Ontario, Canada. We included a total of 36 functional traits related to productivity, competitive ability, reproduction, disturbance tolerance, life history, and tolerance to habitat instability. Using nested ANOVA, we examined the response of diversity indices to disturbance and whether it followed the intermediate disturbance hypothesis (IDH) and varied with habitat stability. We found that, like species richness and diversity, functional richness and diversity reached peaks at moderate disturbance intensity; functional diversity followed the predictions of the IDH. Second, disturbance–habitat‐stability coupling has very little effect on overall species and functional diversity, but the effect on particular life forms and functions may be significant. Since species richness and diversity patterns are context and system dependent, our findings should be most applicable to similar temperate riparian systems.

Monitoring habitat-forming species, such as scleractinian corals, is crucial for managing ecosystems and biodiversity. Yet for assessing population health, challenges remain in reconciling conventional areal coverage surveys with individual-based demographic techniques. Here, we explore both monitoring approaches to characterize the population dynamics of the reef-building coral, Acropora cf. digitifera, on a West Pacific outer reef using photogrammetry reef mapping data spanning 5 years. Tracking 906 coral colonies showed that those exceeding approximately 10 cm diameter exhibit the fastest planar growth but also suffer excess mortality, possibly owing to increased structural vulnerability to dislodgement by wave energy or to other factors, such as disease or predation, that may be exacerbated by senescence. Area-controlled orthomosaic subsampling paired to integral projection modelling revealed a consistent decline in population density, as recruitment was insufficient to balance losses of larger colonies. Yet, total areal coverage and median colony size increased over the study, suggesting this disequilibrium population is on a recovery trajectory from past disturbance and heavily reliant on sporadic recruitment pulses not detected in our study. We find that conventional areal monitoring and demographic approaches can yield contrasting conclusions about population dynamics. Reconciling these differences for disequilibrium populations requires long-term demographic data over periods long enough to detect infrequent yet critical demographic events such as large post-disturbance recruitment events.