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Research Highlight: Sivault, E., Kollross, J., Jorge, L., Finnie, S., Diez Mendez, D., Fernandez Garzon, S., Maraia, H., Lenc, J., Libra, M., Masashi, M., Nakaji, T., Nakamura, M., Sreekar, R., Sam, L., Abe, T., Weiss, M., & Sam, K. (2024). Insectivorous birds and bats outperform ants in the top‐down regulation of arthropods across strata of a Japanese temperate forest. Journal of Animal Ecology.https://doi.org/10.1111/1365‐2656.14146. Top‐down predators exert strong effects on prey populations. Theoretical and empirical studies investigating the cascading effects of predators on biodiversity dynamics and ecosystem functionality have been central to advancing ecology and conservation biology. Yet, how intraguild predation and niche overlap drive the strength and direction of trophic cascades across forest strata is still barely understood. In a study published in this issue, Sivault et al. (2024) investigated the impacts of excluding vertebrate (birds and bats) and invertebrate (ants) predators on arthropod herbivores and plant damage in understory and canopy forest strata. The study finds that birds and bats (but not ants) have negative impacts on herbivore density, which, in turn, benefits plants by reducing leaf damage. Additionally, the effects of vertebrate predators are similar across strata. The authors also show that herbivore density and herbivory are greater in the understory compared to the canopy strata. Sivault et al. (2024) demonstrate that intraguild predation and niche overlap dictate the strength and direction of trophic cascades in forest ecosystems. In addition, these findings shed new light on forest ecology and conservation, especially considering the potential negative effects of climate change on top predators. [ABSTRACT FROM AUTHOR]

Trophic relationships shape ecosystem structure by regulating energy flow and nutrient cycling, impacting prey consumption and prompting behavioral adaptations in prey species to mitigate risks. While much is known about fish antipredator behavior in marine environments, less is understood about these dynamics in freshwater environments. We investigated the antipredator behavior of an Amazonian floodplain fish, Crenuchus spilurus, across different habitat structural complexities. Through experiments, we examined how the number of individuals (1 and 4 individuals) and habitat structural complexity (low, medium, high, and very high) influence the fish response to predator presence. Small groups showed longer flight initiation distance (FID) than solitary individuals, suggesting a possible collective defense strategy against approaching predators. The structural complexity of the habitat did not have a direct effect on FID. Additionally, we noted variations in refuge usage by the fish across different habitat structural complexities. These findings underscore the interplay between behavioral and environmental factors in prey adaptation to predation risk in aquatic ecosystems. [ABSTRACT FROM AUTHOR]

For practical reasons, assessments of species' vulnerability to rising temperatures are often limited to measuring responses to a single ecological response variable, but this could result in an underestimation of vulnerability. Using the Cape Rockjumper Chaetops frenatus ('Rockjumper') we examined the thermal risk to nestling Rockjumpers for sublethal (i.e. reduced nestling mass gain) and lethal (i.e. increased nest predation) consequences of sustained hot weather under both current and predicted future climatic conditions (RCP 8.5). We used a direct approach to examine these risks, first as independent ecological responses and then as combined risk driven by both response variables (mass gain and predation risk). This study revealed that the inclusion of multiple climate‐related responses affected the predicted vulnerability to climate change. Further, our analyses showed that increased vulnerability to climate change will vary within the Rockjumper's habitat. Our results demonstrate that the variability in predicted thermal risk depends on which response variable was used, with implications for how and where conservation practitioners direct their already limited resources. [ABSTRACT FROM AUTHOR]

Foraging decisions shape the structure of food webs. Therefore, a behavioural shift in a single species can potentially modify resource‐flow dynamics of entire ecosystems. To examine this, we conducted a field experiment to assess foraging niche dynamics of semi‐arboreal brown anole lizards in the presence/absence of predatory ground‐dwelling curly‐tailed lizards in a replicated set of island ecosystems. One year after experimental translocation, brown anoles exposed to these predators had drastically increased perch height and reduced consumption of marine‐derived food resources. This foraging niche shift altered marine‐to‐terrestrial resource‐flow dynamics and persisted in the diets of the first‐generation offspring. Furthermore, female lizards that displayed more risk‐taking behaviours consumed more marine prey on islands with predators present. Our results show how predator‐driven rapid behavioural shifts can alter food‐web connectivity between oceanic and terrestrial ecosystems and underscore the importance of studying behaviour‐mediated niche shifts to understand ecosystem functioning in rapidly changing environments. [ABSTRACT FROM AUTHOR]

Urbanisation is one of the main drivers of insect species loss worldwide. However, its impacts on ecological interactions involving insects still deserve further research, especially seed predation and parasitism of seed predators.Here, we evaluated the seed predation rate by the specialist bruchid beetle Pseudopachymerina spinipes and its parasitism rate in the native tree Vachellia caven (Fabaceae) along an urbanisation gradient in Cordoba (Argentina). Since resource availability can influence these ecological interactions, we also investigated whether seed and prey availability could affect seed predation and parasitism rates, respectively.We sampled trees in 10 sampling sites along an urbanisation gradient estimated by the Normalised Difference Vegetation Index (NDVI) within a 100 m radius. In our system, sites with low NDVI, beyond representing the low amount of vegetation cover, also indicate high surface temperature and low availability of host trees.Seed predation in V. caven and the parasitism rate of P. spinipes were significantly reduced with increasing urbanisation. Notably, seed availability at the pod level did not affect seed predation rate, while prey availability was negatively correlated with parasitism rate.These findings suggest a deleterious effect of urbanisation on the studied antagonistic interactions, giving no support to the idea of resource limitation effects. [ABSTRACT FROM AUTHOR]

An organism's body size plays an important role in ecological interactions such as predator–prey relationships. As predators are typically larger than their prey, this often leads to a strong positive relationship between body size and trophic position in aquatic ecosystems. The distribution of body sizes in a community can thus be an indicator of the strengths of predator–prey interactions. The aim of this study was to gain more insight into the relationship between fish body size distribution and trophic position in a wide range of European lakes. We used quantile regression to examine the relationship between fish species' trophic position and their log‐transformed maximum body mass for 48 fish species found in 235 European lakes. Subsequently, we examined whether the slopes of the continuous community size distributions, estimated by maximum likelihood, were predicted by trophic position, predator–prey mass ratio (PPMR), or abundance (number per unit effort) of fish communities in these lakes. We found a positive linear relationship between species' maximum body mass and average trophic position in fishes only for the 75% quantile, contrasting our expectation that species' trophic position systematically increases with maximum body mass for fish species in European lakes. Consequently, the size spectrum slope was not related to the average community trophic position, but there were negative effects of community PPMR and total fish abundance on the size spectrum slope. We conclude that predator–prey interactions likely do not contribute strongly to shaping community size distributions in these lakes. [ABSTRACT FROM AUTHOR]

Habitat degradation is pervasive across the tropics and is particularly acute in Southeast Asia, with major implications for biodiversity. Much research has addressed the impact of degradation on species diversity; however, little is known about how ecological interactions are altered, including those that constitute important ecosystem functions such as consumption of herbivores. To examine how rainforest degradation alters trophic interaction networks, we applied DNA metabarcoding to construct interaction networks linking forest‐dwelling insectivorous bat species and their prey, comparing old‐growth forest and forest degraded by logging in Sabah, Borneo. Individual bats in logged rainforest consumed a lower richness of prey than those in old‐growth forest. As a result, interaction networks in logged forests had a less nested structure. These network structures were associated with reduced network redundancy and thus increased vulnerability to perturbations in logged forests. Our results show how ecological interactions change between old‐growth and logged forests, with potentially negative implications for ecosystem function and network stability. [ABSTRACT FROM AUTHOR]

Habitat structure and predation are major factors that influence the distribution of zooplankton species and functional traits. Here, we analyzed how the structure provided by macrophytes (richness, Shannon's diversity, and biomass) and potential predation by small-bodied fishes (richness and abundance) determine the richness of species and functional traits of zooplankton, as well as the spatial dissimilarity (beta-diversity) of species and traits. Zooplankton, fish, and macrophytes were simultaneously sampled across a gradient of 30 multi-species macrophyte beds. We assessed spatial patterns of zooplankton under taxonomic and functional approaches, using linear regression models, Generalized Dissimilarity Models, a Structural Equation Model, and a Fourth-Corner Analysis. Zooplankton taxonomic beta-diversity was most represented by the turnover component and zooplankton functional beta-diversity by nestedness. Zooplankton taxonomic richness and taxonomic beta-diversity were positively related to macrophyte biomass, richness, and Shannon's diversity, whereas zooplankton functional richness and functional beta-diversity were positively related to fish richness and abundance. Macrophyte biomass and diversity oppositely influenced fish structure, which had influence on zooplankton structure. Macrophytes also negatively influenced the zooplankton traits such as body size, reproduction type, habitat, lifespan, and predatory escape response and positively influenced the trait feeding type. Fish were negatively related to the trait body size. The spatial structure generated by macrophyte beds and fish community determined the distribution of zooplankton species and functional traits. [ABSTRACT FROM AUTHOR]

Interactions between species and individuals can determine their survival in the wild. Most of the time these relationships are difficult to study in situ by direct observation. However, technology can help collect these data with minimal impact on animals' behaviour. Egg stage is certainly the most vulnerable life stage in crocodilians, but few studies have focused on animal species visiting crocodilian nests and associated egg predation. Herein, we use camera-traps in four Mexican states (Chiapas, Oaxaca, Jalisco, Tabasco) to determine vertebrate species and egg predators associated with wild nests of Caiman crocodilus chiapasius, Crocodylus acutus and Crocodylus moreletii. We recorded 72 species of vertebrates at nesting sites and obtained the first photographic evidence of crocodilian egg predation by Caracara cheriway, Cuniculus paca, Didelphis virginiana and Procyon lotor. We also identified commensalism, cooperation, and predation as types of interactions within observed nesting areas, which indicates the importance of crocodilian nesting areas for other wild vertebrates. Finally, we found that crocodilian egg predation depends on species richness present in the area of study, as well as crocodilian size. [ABSTRACT FROM AUTHOR]

The effect of ocean warming and acidification on predator-prey interactions in the intertidal zone is a topic of growing concern for the scientific community. In this review, we aim to describe how scientists have explored the topic via research weaving, a combination of a systematic review, and a bibliometric approach. We assess articles published in the last decade exploring the impact of both stressors on predation in the intertidal zone, via experimental or observational techniques. Several methods were used to delve into how climate change-induced stress affected intertidal predation, as the study design leaned toward single-based driver trials to the detriment of a multi-driver approach. Mollusks, echinoderms, and crustaceans have been extensively used as model organisms, with little published data on other invertebrates, vertebrates, and algae taxa. Moreover, there is a strong web of co-authoring across institutions and countries from the Northern Hemisphere, that can skew our understanding towards temperate environments. Therefore, institutions and countries should increase participation in the southern hemisphere networking, assessing the problems under a global outlook. Our review also addresses the various impacts of ocean acidification, warming, or their interaction with predation-related variables, affecting organisms from the genetic to a broader ecological scope, such as animal behaviour or interspecific interactions. Finally, we argue that the numerous synonyms used in keywording articles in the field, possibly hurting future reviews in the area, as we provide different keyword standardizations. Our findings can help guide upcoming approaches to the topic by assessing what has been already done and revealing gaps in emerging themes, like a strong skew towards single-driver (specially acidification) lab experiments of northern hemisphere organisms and a lack of field multi-stressor experiments. • Review about climate change impacts on intertidal predator-prey interaction. • Research weaving focusing on the scientific literature from the 2010's • Prevalence of single-stressor acidification studies about invertebrates • Countries need to expand their collaborations towards the southern hemisphere • Lack of standardization of keywords may be hindering future reviews about the field [ABSTRACT FROM AUTHOR]

Mobbing represents a well‐known anti‐predatory behavior, where potential prey display aggressively against a predator. Despite considerable experimental and descriptive work, no models predict species participation in mobbing assemblages. Here, we aimed to understand why some bird species engage in this behavior, while others do not, and what factors can be used to predict mobbing engagement within an avian community. We investigated whether certain functional traits, such as body size, foraging guild, foraging mode, and strata, as well species abundance and evolutionary relatedness, are important mobbing predictors. To address these goals, we simulated the presence of the Ferruginous Pygmy‐Owl (Glaucidium brasilianum) by broadcasting its voice in 230 experiments conducted in 115 points, systematically distributed in a dry forest of northeastern Brazil. We compared these results to 162 avian surveys (point counts) conducted in the same area. Our avian surveys detected 108 bird species (local avian community), whereas our playback experiments attracted 72 species (mobbing assemblage). In general, small, canopy insectivorous or frugivorous birds dominated the mobs. The best mobbing predictors were body mass and guild, whereas species abundance, foraging mode, and strata were not retained in the best models. We found a strong phylogenetic component in body mass and mobbing propensity (almost 90% of the species and individuals participating in the mobs were passerines). At the community level, we found significant differences in the functional and phylogenetic structure of the mobbing assemblage in relation to the avian community. Our results suggest that mobbing behavior is tightly associated with predation risk and the capacity of individual species to find and detect predators, and that functional and phylogenetic features can predict species participation in this complex animal behavior. In this study, we investigate whether certain functional traits, such as body size, foraging guild, foraging mode, and strata, as well as evolutionary relatedness, are important mobbing predictors. We compared the mobbing avian assemblage obtained with 230 playback experiments simulating the presence of the Ferruginous Pygmy‐Owl (Glaucidium brasilianum) with 162 independent point counts aimed to survey the area's avifauna in a dry forest of northeastern Brazil. We found significant differences in the functional and phylogenetic structure of the mobbing assemblage in relation to the avian community. Our results suggest that mobbing behavior is tightly associated with predation risk and the capacity of individual species to find and detect predators, indicating that functional and phylogenetic features can predict species participation in this complex animal behavior. [ABSTRACT FROM AUTHOR]

Abstract: Invasive fish threaten many native freshwater fauna. However, it can be difficult to determine how invasive fish impact animals with complex life cycles as interaction may be driven by either predation of aquatic larvae or avoidance of fish‐occupied waterbodies by the terrestrial adult stage. Mosquitofish (Gambusia spp.) are highly successful and aggressive invaders that negatively impact numerous aquatic fauna. One species potentially threatened by Gambusia holbrooki is the green and golden bell frog (Litoria aurea). However, G. holbrooki's role in this frog's decline was unclear due to declines driven by the chytrid fungal disease and the continued co‐existence of these fish and frogs in multiple locations. To clarify the extent to which Gambusia is impacting L. aurea, we conducted 3 years of field surveys across a deltaic wetland system in south‐east Australia. We measured the presence and abundance of aquatic taxa including G. holbrooki, and L. aurea frogs and tadpoles, along with habitat parameters at the landscape and microhabitat scale. Generalized linear models were used to explore patterns in the abundance and distributions of L. aurea and G. holbrooki. We found strong negative associations between G. holbrooki and tadpoles of most species, including L. aurea, but no apparent avoidance of G. holbrooki by adult frogs. Native invertebrate predators (Odonata and Coleoptera) were also absent from G. holbrooki‐occupied ponds. Due to the apparent naivety of adult frogs toward G. holbrooki, the separation of G. holbrooki and tadpoles, plus the abundance of alternative predators in G. holbrooki‐free ponds, we conclude that the impact of G. holbrooki on L. aurea recruitment is likely substantial and warrants management action. [ABSTRACT FROM AUTHOR]

Abstract: Most studies regarding ant–aphid interactions focus only on the direct effects of ants on tended aphids and aphidophagous predators, or the indirect effects on the host plant. Studies evaluating the effects of aphid‐tending ants on more than one trophic level are rare and evaluate only the presence or absence of such effects. Here we assessed the effect sizes of ants in a tri‐trophic system (common bean plants, aphids and lacewing larvae). We tested if the presence of aphid‐tending ants has positive effects on aphid abundance and host‐plant production and negative effects on aphid predator abundance. We also hypothesized that aphid‐tending ants affect more intensely trophic levels that are more directly related to them (i.e., first aphids, then aphid predators and then host plants). We tested these hypotheses in field mesocosms experiments using the presence and absence of ants. We found that aphid‐tending ants have great positive effects on final aphid abundance. Ants also positively affected the number of seeds; however, it was not possible to measure the effect size for this trophic level. Furthermore, ants had negative effects on lacewing larvae only at first release. The effect size of ants was greater for aphids, followed by lacewing larvae, and with no effects on the number of seeds produced. Ants positively affect aphids and host‐plant production, probably by way of honeydew collection preventing the development of entomophagous/saprophytic fungi. On the other hand, ants negatively affect lacewing larvae by excluding them from the host plant. In natural systems, several ant species may attend aphids, differently affecting the organisms of the various trophic levels within the ant–aphid interaction, thereby obscuring the real effect size of ants. Assessing the effect size of aphid‐tending ants on the organisms involved in ant–aphid interactions provides more realistic information about the effects of this interaction on natural systems. [ABSTRACT FROM AUTHOR]

Aim The elucidation of patterns and drivers of community assembly remains a fundamental issue in ecology. Past studies have focused on a limited number of communities at local or regional scales, thus precluding a comprehensive examination of assembly rules. We addressed this challenge by examining stream fish community assembly within numerous independent watersheds spanning a broad environmental gradient. We aimed to answer the following questions: (1) are fish communities structured non-randomly, and (2) what is the relative importance of environmental filtering, predator-prey interactions and interspecific competition in driving species associations? Location The conterminous USA. Methods We used null models to analyse species associations in streams. Non-random communities were defined as those where the summed number of segregated and aggregated species pairs exceeded the number expected by chance. We used species traits to characterize species dissimilarity in environmental requirements (ENV), identify potential predator-prey interactions (PRED) and estimate likely degree of competition based on species similarity in body size, feeding strategies and phylogeny (COMP). To evaluate the effect of environmental filtering, predation and competition on species associations, we related ENV, PRED and COMP to the degree of species segregation. Results The majority (75-85%) of watersheds had non-random fish communities. Species segregation increased with species dissimilarity in environmental requirements (ENV). An increase in competition strength (COMP) did not appear to increase segregation. Species pairs engaging in predator-prey interactions (PRED) were more segregated than non-predator-prey pairs. ENV was more predictive of the degree of species segregation than PRED. Main conclusions We provide compelling evidence for widespread non-random structure in US stream fish communities. Community assembly is governed largely by environmental filtering, followed by predator-prey interactions, whereas the influence of interspecific competition appears minimal. Applying a traits-based approach to continent-wide datasets provides a powerful approach for examining the existence of assembly rules in nature. [ABSTRACT FROM AUTHOR]

In New Zealand and Australia, rural landowners believe that local predator control to protect indigenous biota exacerbates European rabbit O ryctolagus cuniculus problems on their land. We assess the validity of their concerns by reviewing the published literature on effects of predators on rabbit abundance., In New Zealand, where rabbits and their predators are introduced, predators appear to have relatively little effect on rabbit numbers compared with other factors leading to mortality, such as disease, flooding of burrows and burrow collapse. Similarly, in Australia, rabbit numbers are driven primarily by climate and its effects on food abundance and quality, and by disease. However, where rabbit numbers are low following drought or major epizootics, predation can limit population recovery. In the Iberian Peninsula, where rabbits and their predators are indigenous, the effects of predators are unknown, as they are often confounded by other factors. Rabbit numbers are influenced mostly by habitat, food, disease and rainfall. Elsewhere in Europe, predators have their strongest effect when rabbit numbers have been reduced by other factors, but have little effect on high-density rabbit populations., In Australasia, abundance of predators (especially rabbit specialists) can usually be predicted from rabbit abundance, not vice versa. Although predation effects can be limiting under certain conditions, they are minor compared to the roles of climate, food, disease and habitat., A key unresolved question is whether those circumstances where predator control might lead to increases in rabbit populations can be identified with enough certainty to allow reliable predictions to be generated. One approach is to implement robust rabbit, predator and disease monitoring programmes at sites with predator control operations. Data on changes in rabbits, predators, and disease prevalence could be combined with local data on other key factors to facilitate reasonable inference about effects of predators on rabbits. The inclusion of carefully matched non-treatment areas is crucial if such programmes are to succeed. [ABSTRACT FROM AUTHOR]

Groups of organisms often have congruent patterns of diversity or community structure due to similar environmental requirements. However, ecological interactions across trophic levels may also promote congruence independent of environmental drivers through selective predation, niche partitioning, or facilitation. We examined congruence between phytoplankton and zooplankton communities using 20 years of monitoring data from 17 Danish lakes, most of which were subject to external nutrient loading reduction after a period of eutrophication. Linear mixed effect models and partial Mantel tests were used to elucidate the extent to which congruence in genus richness and composition was driven by environmental factors. Congruence not explained by environmental controls might indicate ecological interactions across trophic levels of lake plankton. Genus richness and composition of phyto- and zooplankton were significantly congruent. Environmental factors had limited power to explain the genus richness of phyto- and zooplankton (R²: 6% and 12%, respectively). Including richness of the reciprocal group among the predictors markedly improved each respective model and explanatory power (R²: 11% and 17%, respectively). Similarly, a large proportion of the congruence in genus composition was independent of environmental dissimilarity (Mantel r: 0.29 and partial Mantel r after accounting for environmental control: 0.17). The strength of the congruence varied among different groups of phyto- and zooplankton, likely reflecting that the different zooplankton groups differ in their grazing size spectra and thus in the strength of their coupling with the phytoplankton assemblages. Remarkably, congruence with phytoplankton was strongest for the smallest group of zooplankton, rotifers, which graze on a limited size spectrum of phytoplankton. Moreover, congruence was stronger in low-nutrient lakes, suggesting that the strength of the interactions between the two groups weakens with eutrophication. This is likely due to changes in trophic dynamics, where enhanced fish predation on large-bodied zooplankton with increasing nutrient levels results in reduced zooplankton grazing control of phytoplankton assemblages. [ABSTRACT FROM AUTHOR]

Species interactions such as predation or competition can have notable implications for fish population dynamics. Stock status and associated biological reference points can be misrepresented if these interactions are not considered. Here we present a multispecies, biomass production model (MS-PROD) developed by incorporating modifications to the Schaefer production model. The modifications explicitly emphasize a functional group approach, highlighting the effects of species interactions that include competition between species within a group, competition between groups, and predation. The mathematical formulation also includes constraints on carrying capacity for both the entire system and for individual groups. We applied the model as initialized to the Northeast U.S. Large Marine Ecosystem finfish community. We then executed simulations designed to explore the behavior of the model with respect to fishery exploitation and ecological interactions. Collectively, the results demonstrated the utility, and the need, for incorporating ecological effects into fisheries models. [Copyright &y& Elsevier]

Selected cases of plankton studies were analyzed to illustrate the main types of relationships between the zooplankton and the ichthyoplankton abundance observed in the pelagic realm. Such relationships may exhibit a positive, a negative, or a random pattern. In the conceptual model here proposed, short-term oscillations among these patterns were attributed to small-scale biological processes, such as competition, predation, and intraguild predation, acting in conjunction with water turbulence. A negative relationship between zooplankton and ichthyoplankton abundance may be caused both by predation on fish eggs and larvae, and by detrimental competition and intraguild predation interactions for fish larvae. In contrast, positive relationships emerge from the absence or low abundance of major predators on the ichthyoplankton, and from food availability for fish larvae and competing species. The random pattern may appear as a gradual transitional stage between the negative and positive patterns, or be promoted by strong water turbulence – which generates random movements of individuals. The size of zooplankters greatly influences these small-scale phenomena. Hence, their role in the trophic web, the success in competition interactions and vulnerability to water turbulence depends on their size. Intra- and interspecific competition may be reduced by variability in body size within or among fish larvae populations. Owing to a strong interaction among phenomena at different scales, these small-scale processes are also influenced by larger scale features, such as seasonal changes in zooplankton biomass, water currents, or spawning periods of fish. At the space level, some theoretical studies have emphasized the role of water currents as a vector for fish larvae to reach the nursery grounds (migration triangle hypothesis), or to allow them to remain within their own population’s distributional area (member/vagrant hypothesis). At the temporal level, the match/mismatch theory insists in a synchrony between reproductive strategies of fish and cyclical changes in abundance and size spectrum of potential prey items for their larvae. In any case, a coincidence between favorable abiotic and biotic features during the whole life-cycle of fish would assure a success in survival of larvae and their subsequent recruitment to adult population. [ABSTRACT FROM AUTHOR]

We assessed the relation between abundance of desert pupfish,Cyprinodon macularius, and selected biological and physicochemical variables in natural and manmade habitats within the Salton Sea Basin. Field sampling in a natural tributary, Salt Creek, and three agricultural drains captured eight species including pupfish (1.1% of the total catch), the only native species encountered. According to Bray-Curtis resemblance functions, fish species assemblages differed mostly between Salt Creek and the drains (i.e., the three drains had relatively similar species assemblages). Pupfish numbers and environmental variables varied among sites and sample periods. Canonical correlation showed that pupfish abundance was positively correlated with abundance of western mosquitofish,Gambusia affinis, and negatively correlated with abundance of porthole livebearers,Poeciliopsis gracilis, tilapias (Sarotherodon mossambicaandTilapiazillii), longjaw mudsuckers,Gillichthys mirabilis, and mollies (Poecilia latipinnaandPoecilia mexicana). In addition, pupfish abundance was positively correlated with cover, pH, and salinity, and negatively correlated with sediment factor (a measure of sediment grain size) and dissolved oxygen. Pupfish abundance was generally highest in habitats where water quality extremes (especially high pH and salinity, and low dissolved oxygen) seemingly limited the occurrence of nonnative fishes. This study also documented evidence of predation by mudsuckers on pupfish. These findings support the contention of many resource managers that pupfish populations are adversely influenced by ecological interactions with nonnative fishes. [ABSTRACT FROM AUTHOR]

This study describes assemblages of predatory ground beetles in native birch forest and derived blueberry farms on the Lower Mainland of British Columbia and investigates their role in the successful biological control of winter moth (Operopthera brumata L.) by the parasitoid Cyzenis albicans Falle´n. Pitfall traps at four sites in 1991 and 1992 indicated that natural birch forest was dominated by native carabid species, while open blueberry was dominated by introduced species and some native xerophilous species. Predation by generalist invertebrates was an important mortality factor for both winter moth and C. albicans at all sites and was greatest in the first 2 weeks after pupation. Ground beetles including Harpalus affinus (Schrank) and Pterostichus spp. consumed winter moth pupae in arenas but adult beetles rarely consumed C. albicans pupae. Much of the overall predation was due to smaller invertebrates including beetle larvae. Predators actively searched for buried pupae and selected among pupal types based on condition (dead, parasitised or healthy) and size. Prey-selection differed among sites but C. albicans pupae were preferred at three of the four sites. At the remaining site, an organic blueberry farm, over 90% of both parasitised and healthy pupae were consumed. High levels of predation did not affect the levels of parasitism by C. albicans at the sites. This herbivore–parasitoid–predator system demonstrates the importance of naturally occurring predatory invertebrates for successful integrated pest management, even where they prey upon a biological control agent. [Copyright &y& Elsevier]

Pesticides released to the environment can indirectly affect target and non-target species in ways that are often contrary to their intended use. Such indirect effects are mediated through direct impacts on other species or the physical environment and depend on ecological mechanisms and species interactions. Typical mechanisms are the release of herbivores from predation and release from competition among species with similar niches. Application of insecticides to agriculture often results in subsequent pest outbreaks due to the elimination of natural enemies. The loss of floristic diversity and food resources that result from herbicide applications can reduce populations of pollinators and natural enemies of crop pests. In aquatic ecosystems, insecticides and fungicides often induce algae blooms as the chemicals reduce grazing by zooplankton and benthic herbivores. Increases in periphyton biomass typically result in the replacement of arthropods with more tolerant species such as snails, worms and tadpoles. Fungicides and systemic insecticides also reduce nutrient recycling by impairing the ability of detritivorous arthropods. Residues of herbicides can reduce the biomass of macrophytes in ponds and wetlands, indirectly affecting the protection and breeding of predatory insects in that environment. The direct impacts of pesticides in the environment are therefore either amplified or compensated by their indirect effects. [ABSTRACT FROM AUTHOR]