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For marine species with planktonic dispersal, invasion of open ocean coastlines is impaired by the physical adversity of ocean currents moving larvae downstream and offshore. The extent species are affected by physical adversity depends on interactions of the currents with larval life history traits such as planktonic duration, depth and seasonality. Ecologists have struggled to understand how these traits expose species to adverse ocean currents and affect their ability to persist when introduced to novel habitat. We use a high‐resolution global ocean model to isolate the role of ocean currents on the persistence of a larval‐producing species introduced to every open coastline of the world. We find physical adversity to invasion varies globally by several orders of magnitude. Larval duration is the most influential life history trait because increased duration prolongs species' exposure to ocean currents. Furthermore, variation of physical adversity with life history elucidates how trade‐offs between dispersal traits vary globally. [ABSTRACT FROM AUTHOR]

Predation is a dominant structuring force in ecological communities. In aquatic environments, predation on bivalves has long been an important focal interaction for ecological study because bivalves have central roles as ecosystem engineers, basal components of food webs, and commercial commodities. Studies of bivalves are common, not only because of bivalves' central roles, but also due to the relative ease of studying predatory effects on this taxonomic group. To understand patterns in the interactions of bivalves and their predators we synthesised data from 52 years of peer‐reviewed studies on bivalve predation. Using a systematic search, we compiled 1334 studies from 75 countries, comprising 61 bivalve families (N = 2259), dominated by Mytilidae (29% of bivalves), Veneridae (14%), Ostreidae (8%), Unionidae (7%), and Dreissenidae and Tellinidae (6% each). A total of 2036 predators were studied, with crustaceans the most studied predator group (34% of predators), followed by fishes (24%), molluscs (17%), echinoderms (10%) and birds (6%). The majority of studies (86%) were conducted in marine systems, in part driven by the high commercial value of marine bivalves. Studies in freshwater ecosystems were dominated by non‐native bivalves and non‐native predator species, which probably reflects the important role of biological invasions affecting freshwater biodiversity. In fact, while 81% of the studied marine bivalve species were native, only 50% of the freshwater species were native to the system. In terms of approach, most studies used predation trials, visual analysis of digested contents and exclusion experiments to assess the effects of predation. These studies reflect that many factors influence bivalve predation depending on the species studied, including (i) species traits (e.g. behaviour, morphology, defence mechanisms), (ii) other biotic interactions (e.g. presence of competitors, parasites or diseases), and (iii) environmental context (e.g. temperature, current velocity, beach exposure, habitat complexity). There is a lack of research on the effects of bivalve predation at the population and community and ecosystem levels (only 7% and 0.5% of studies respectively examined impacts at these levels). At the population level, the available studies demonstrate that predation can decrease bivalve density through consumption or the reduction of recruitment. At the community and ecosystem level, predation can trigger effects that cascade through trophic levels or effects that alter the ecological functions bivalves perform. Given the conservation and commercial importance of many bivalve species, studies of predation should be pursued in the context of global change, particularly climate change, acidification and biological invasions. [ABSTRACT FROM AUTHOR]

Ecosystem engineers (EEs) strongly influence ecosystems by affecting the abiotic properties of a system to which many biota respond. EEs can, thus, be pivotal species in restoration by helping to move systems toward desired states much faster and more efficiently than direct human intervention on the abiotic state.For EEs to play a central, purposeful role in restoration, it is important to identify guiding principles about how the EEs may best be selected and incorporated.I discuss three important aspects to determine (a) where the utility for EEs is high; (b) where EEs can most easily establish, are easy to handle and scaling‐up their use is possible; and (c) how to recognize and value multiple, coupled and trait‐dependent engineering functions of EEs.Understanding these aspects of EEs should help guide purposeful and efficient choices in our approach to restoration. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Parasitism rates can vary dramatically across large and small spatial scales. Such heterogeneity in infection is driven by variation in environmental factors that influence the probability of host and parasite encountering each other (encounter filters) and of genetic and physiological factors that alter whether that encounter results in a successful infection (compatibility filters). Here, we investigated how infection in first‐intermediate hosts (snails) by trematode parasites is influenced by small‐scale variation in environmental variables (final host relative abundance, nutrients, and temperature) and population origin across multiple ponds within an artificial flow‐through wetland system in Atlanta, GA, U.S.A.We placed individually marked, lab‐reared F1 generation snails of the same age from three different populations into field enclosures at nine ponds along a 1‐km stretch of connected, flow‐through ponds for 86 days and allowed them to accrue infections naturally. This highly controlled field experiment allowed us to disentangle the underlying factors influencing small‐scale variation in infection risk, which can be masked when looking only at natural patterns of infection prevalence across space.We found high heterogeneity in infection risk. The probability of infection was highest in ponds downstream and with high levels of bird activity; population origin was not important.This work provides experimental evidence that infection risk varies across small spatial scales (tens of metres), driven by steep gradients in influential environmental drivers, emphasising the importance of controlled field manipulations to understand infection risk. Identifying small‐scale drivers of infection risk can help mitigate infection in hosts of interest (e.g., humans, fish), and should be acknowledged in organismal field studies, where infection and infection risk may influence the ecology, physiology, or behaviour of animals. [ABSTRACT FROM AUTHOR]

Examining community responses to habitat configuration across scales informs basic and applied models of ecosystem function. Responses to patch‐scale edge effects (i.e., ecological differences between patch edges and interiors) are hypothesized to underpin the effects of landscape‐scale fragmentation (i.e., mosaics of multipatch habitat and matrix). Conceptually, this appears justifiable because fragmented habitats typically have a greater proportion of edge than continuous habitats. To critically inspect whether patch‐scale edge effects translate consistently (i.e., scale up) into patterns observed in fragmented landscapes, we conducted a meta‐analysis on community relationships in seagrass ecosystems to synthesize evidence of edge and fragmentation effects on shoot density, faunal densities, and predation rates. We determined effect sizes by calculating log response ratios for responses within patch edges versus interiors to quantify edge effects, and fragmented versus continuous landscapes to quantify fragmentation effects. We found that both edge and fragmentation effects reduced seagrass shoot densities, although the effect of edge was statistically stronger. By contrast, fauna often exhibited higher densities in patch edges, while fragmentation responses varied directionally across taxa. Fish densities trended higher in patch edges and fragmented landscapes. Benthic fishes responded more positively than benthopelagic fishes to edge effects, although neither guild strongly responded to fragmentation. Invertebrate densities increased in patch edges and trended lower in fragmented landscapes; however, these were small effect sizes due to the offsetting responses of two dominant epifaunal guilds: decapods and smaller crustaceans. Edge and fragmentation affected predation similarly, with prey survival trending lower in patch edges and fragmented landscapes. Overall, several similarities suggested that edge effects conform with patterns of community dynamics in fragmented seagrass. However, across all metrics except fish densities, variability in fragmentation effects was twice that of edge effects. Variance patterns combined with generally stronger responses to edge than fragmentation, warrant caution in unilaterally "scaling‐up" edge effects to describe fragmentation effects. Alternatively, fragmentation includes additional factors (e.g., matrix effects, patch number, mean patch size, isolation) that may enhance or offset edge effects. Fragmentation and increased edge are syndromes of habitat degradation, therefore this analysis informs mechanistic models of community change in altered terrestrial and marine systems. [ABSTRACT FROM AUTHOR]

Single‐gene markers, such as the mitochondrial cox1, microsatellites, and single‐nucleotide polymorphisms are powerful methods to describe diversity within and among taxonomic groups and characterize phylogeographic patterns. Large repositories of publicly‐available, molecular data can be combined to generate and evaluate evolutionary hypotheses for many species, including algae. In the case of biological invasions, the combination of different molecular markers has enabled the description of the geographic distribution of invasive lineages. Here, we review the phylogeography of the widespread invasive red macroalga Agarophyton vermiculophyllum (synonym Gracilaria vermiculophylla). The cox1 barcoding provided the first description of the invasion history and hinted at a strong genetic bottleneck during the invasion. Yet, more recent microsatellite and SNP genotyping has not found evidence for bottlenecks and instead suggested that genetically diverse inocula arose from a highly diverse source population, multiple invasions, or some mix of these processes. The bottleneck evident from cox1 barcoding likely reflects the dominance of one mitochondrial lineage, and one haplotype in particular, in the northern source populations in Japan. Recent cox1 sequencing of A. vermiculophyllum has illuminated the complexity of phylogeographic structure in its native range of the northwest Pacific Ocean. For example, the western coast of Honshu in the Sea of Japan displays spatial patterns of haplotypic diversity with multiple lineages found together at the same geographic site. By consolidating the genetic data of this species, we clarify the phylogenetic relationships of a well‐studied macroalga introduced to virtually every temperate estuary of the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Information on parasites and disease in marine ecosystems lags behind terrestrial systems, increasing the challenge of predicting responses of marine host–parasite systems to climate change. However, here I examine several generalizable aspects and research priorities. First, I advocate that quantification and comparison of host and parasite thermal performance curves is a smart approach to improve predictions of temperature effects on disease. Marine invertebrate species are ectothermic and should be highly conducive to this approach given their generally short generation times. Second, in marine systems, shallow subtidal and intertidal areas will experience the biggest temperature swings and thus likely see the most changes to host–parasite dynamics. Third, for some responses like parasite intensity, as long as the lethal limit of the parasite is not crossed, on average, there may be a biological basis to expect temperature-dependent intensification of impacts on hosts. Fourth, because secondary mortality effects and indirect effects of parasites can be very important, we need to study temperature effects on host–parasite dynamics in a community context to truly know their bottom line effects. This includes examining climate-influenced effects of parasites on ecosystem engineers given their pivotal role in communities. Finally, other global change factors, especially hypoxia, salinity, and ocean acidity, covary with temperature change and need to be considered and evaluated when possible for their contributing effects on host–parasite systems. Climate change–disease interactions in nearshore marine environments are complex; however, generalities are possible and continued research, especially in the areas outlined here, will improve our understanding. Information on parasites and disease in marine ecosystems lags behind terrestrial systems, increasing the challenge of predicting responses of marine host-parasite systems to climate change. This Essay highlights five general principles to guide the study of the response of marine host-parasite interactions to climate change, including the effects of temperature, oxygen, acidity, and salinity. [ABSTRACT FROM AUTHOR]

Free-living species vary substantially in the extent of their spatial distributions. However, distributions of parasitic species have not been comprehensively compared in this context. We investigated which factors most influence the geographical extent of mammal parasites. Using the Global Mammal Parasite Database we analysed 17 818 individual geospatial records on 1806 parasite species (encompassing viruses, bacteria, protozoa, arthropods and helminths) that infect 396 carnivore, ungulate and primate host species. As a measure of the geographical extent of each parasite species we quantified the number and area of world ecoregions occupied by each. To evaluate the importance of variables influencing the summed area of ecoregions occupied by a parasite species, we used Bayesian network analysis of a subset (n = 866) of the parasites in our database that had at least two host species and complete information on parasite traits. We found that parasites that covered more geographical area had a greater number of host species, higher average phylogenetic relatedness between host species and more sampling effort. Host and parasite taxonomic groups had weak and indirect effects on parasite ecoregion area; parasite transmission mode had virtually no effect. Mechanistically, a greater number of host species probably increases both the collective abundance and habitat breadth of hosts, providing more opportunities for a parasite to have an expansive range. Furthermore, even though mammals are one of the best-studied animal classes, the ecoregion area occupied by their parasites is strongly sensitive to sampling effort, implyingmammal parasites are undersampled. Overall, our results support that parasite geographical extent is largely controlled by host characteristics, many of which are subsumed within host taxonomic identity. [ABSTRACT FROM AUTHOR]

Many communities are shifting composition, with losses of native species and increases of non‐indigenous species (NIS). At its extreme, such alteration of ecological guilds can result in simplification with a single NIS performing an ecological role once carried out by a suite of natives. This alteration has occurred in many rivers of the south‐eastern U.S.A., where the invasive filter‐feeding freshwater clam Corbicula fluminea has proliferated following the nearly complete extirpation of native mussels.We investigated the factors controlling the distribution and abundance of Corbicula, as well as estimated the ecological service it provides via water filtration. With a nested design, we surveyed multiple transects within four to six sites within each of four rivers that spanned three large catchments in the Georgia piedmont, collecting data on Corbicula density and physical habitat characteristics associated with its presence.We found Corbicula present in over half of the 1,536 sampled 0.044 m2 sampled plots, 90 of the 93 transects that spanned the width of the river, and all 1–2 km sample sites, underscoring the clam's ubiquity in the study region. At the river scale, Corbicula densities ranged from 50–212 Corbicula m−2, although individual sites ranged from 7–483 Corbicula m−2. Corbicula was more abundant in areas with higher proportions of gravel, and less abundant with higher proportions of bedrock. A hierarchical model with river, site, and these two substrate variables explained 32% of the variation in Corbicula density.Using observed densities and published per capita feeding rates, we calculated system‐wide collective filtration rates provided by Corbicula. In the four rivers surveyed and based on estimated residence times for median flows for the summer of 2012, Corbicula is estimated to filter water as many as seven times during median flows and 18 times during minimum flows before water flows out of a 10‐km reach. Due to high abundances and per biomass filtration rates, Corbicula plays an important role in these rivers.Invasive species, biotic homogenisation, and the loss of functional redundancy may mean that many more rivers are similar to our studied rivers, with a single, often invasive, species dominating ecosystem function. Understanding the influence of biotic homogenisation on ecosystem function is of foremost importance to evaluate the resilience of natural systems. [ABSTRACT FROM AUTHOR]

Homeowners in coastal environments often augment their access to estuarine ecosystems by building private docks on their personal property. Despite the commonality of docks, particularly in the Southeastern United States, few works have investigated their historical development, their distribution across the landscape, or the environmental justice dimensions of this distribution. In this study, we used historic aerial photography to track the abundance and size of docks across six South Carolina counties from the 1950s to 2016. Across our roughly 60-year study period, dock abundance grew by two orders of magnitude, mean length of newly constructed docks doubled, and the cumulative length of docks ballooned from 34 to 560 km. Additionally, we drew on census data interpolated into consistent 2010 tract boundaries to analyze the racial and economic distribution of docks in 1994, 1999, 2011, and 2016. Racial composition, measured as the percentage of a tract's population that was White, positively correlated with dock abundance in each year. Median household income and dock abundance were only correlated in 2011. Taken together, these metrics indicate the growing desire for direct estuary access, however, that access does not appear to be equally spread across racial groups. Because docks enhance estuarine access and demarcate private property, our study provides longitudinal insights into environmental justice concerns related to disparate private property ownership. We found a persistent correlation between the racial characteristics of an area and dock abundance, strongly indicating that White South Carolinians have had disproportionately greater private water access for the past two decades. [ABSTRACT FROM AUTHOR]

Risk of infection by parasites can be driven by environmental heterogeneity, often at small scales. We quantified the effect of tidal elevation on infection patterns of two lethal parasites, Perkinsus marinus and Haplosporidium nelsoni , in an important coastal species, the eastern oyster, Crassostrea virginica . Within the southeastern US, oysters in Georgia and South Carolina are rarely found in the subtidal zone. Historically, it has been hypothesized that this pattern could be due to the increased exposure of hosts to waterborne parasites. We manipulated oysters at two tidal elevations (intertidal and subtidal) in a Georgia estuary to test if P. marinus , H. nelsoni , and co-infection by both parasites were different between tidal heights. We found that though P. marinus prevalence and co-infection prevalence of both parasites were not significantly different between tidal elevations, as has been found previously, P. marinus intensity and H. nelsoni prevalence were significantly higher intertidally than subtidally. These findings show that parasite infections can be higher in the host's natural (preferred) tidal height, and suggest that longer exposure to parasites in the subtidal is not a likely reason for the paucity of oysters at that tidal elevation in certain regions of the southeastern US. More broadly, our results provide further evidence that environmental effects on host-parasite interactions can vary by parasite species and across small (meter-long) spatial scales. [ABSTRACT FROM AUTHOR]

Movement of individuals links the effects of local variation in habitat quality with growth and persistence of populations at the landscape scale. When the populations themselves are linked by interspecific interactions, such as predation, differential movement between habitats may lead to counterintuitive system-wide dynamics. Understanding the interaction between local drivers and dynamics of widely dispersed species is necessary to predict the impacts of habitat fragmentation and degradation, which may be transmitted across habitat boundaries by species' movements. Here we model predator-prey interactions across unaltered and degraded habitat areas, and we explore the additional effects of adaptive habitat choice by predators on the resilience of prey populations. We show how movement between habitats can produce the 'bad neighbor effect,' in which predators' response to localized habitat degradation causes system-wide loss of prey populations. This effect arises because adaptive foraging results in the concentration of predators in the more productive unaltered habitat, even when this habitat can not support the increased prey mortality. The mechanisms underlying this effect are especially sensitive to prey dispersal rate and adaptive predator behavior. [ABSTRACT FROM AUTHOR]

Parasites can impart heavy fitness costs on their hosts. Thus, understanding the spatial and temporal consistency in parasite pressure can elucidate the likeliness of parasites' role as agents of directional selection, as well as revealing variable environmental factors associated with infection risk. We examined spatiotemporal variation in digenetic trematode infection in 18 populations of an intertidal host snail ( Littorina littorea) over a 300 km range at an 11-yr interval, more than double the generation time of the snail. Despite a complete turnover in the snail host population, the average change in infection prevalence among populations was <1% over the 11-yr span, and all but three populations remained within 5 percentage points. This consistency of prevalence in each population over time suggests remarkable spatiotemporal constancy in parasite delivery vectors in this system, notably gulls that serve as definitive hosts for the parasites. Thus, despite gulls' high mobility, their habitat usage patterns are ostensibly relatively fixed in space. Importantly, this spatiotemporal consistency also implies that sites where parasites are recruitment limited remain so over time, and likewise, that parasite hotspots stay hot. [ABSTRACT FROM AUTHOR]

Species face multiple selective pressures that may require opposing responses to mitigate. On rocky shorelines, fitness of the intertidal snail Littorina littorea is determined by both parasitism and predation. We experimentally demonstrated that L. littorea was at greatest risk of infection from trematode parasites high in the intertidal zone where it was in closest proximity to abundant gull feces (the vector for the snail's parasites). However, because of extreme, size-selective predation pressure at low tidal elevations, small snails often live high in the intertidal until they have grown sufficiently large. By prolonging their exposure to infection higher on the shore, ontogenetic responses to predation risk accentuate parasite risk. Counterintuitively, snails exhibited the highest trematode prevalence at the lowest tidal elevations where they had almost no risk of contracting infection. By carrying contracted infections into the lowest tidal zones, the larger, predation-resistant snails invert hotspots of infection risk and prevalence, underscoring that size-dependent selection pressures can decouple infection process and pattern even over small scales. [ABSTRACT FROM AUTHOR]

Despite knowledge on invasive species' predatory effects, we know little of their influence as prey. Non-native prey should have a neutral to positive effect on native predators by supplementing the prey base. However, if non-native prey displace native prey, then an invader's net influence should depend on both its abundance and value relative to native prey. We conducted a meta-analysis to quantify the effect of non-native prey on native predator populations. Relative to native prey, non-native prey similarly or negatively affect native predators, but only when studies employed a substitutive design that examined the effects of each prey species in isolation from other prey. When native predators had access to non-native and native prey simultaneously, predator abundance increased significantly relative to pre-invasion abundance. Although non-native prey may have a lower per capita value than native prey, they seem to benefit native predators by serving as a supplemental prey resource. [ABSTRACT FROM AUTHOR]

Predator-prey interactions are often highly co-evolved, with selection over time for prey with morphological and behavioral traits that minimize predation risk. Consequently, in many environments prey choose among potential habitats according to their refuge value. It is unclear, however, when presented with new habitats, if prey are able to evaluate the predation risk of these relative to familiar habitats and utilize these in accordance with their value. We tested whether, along the east coast of the USA, native mud crabs Panopeus herbstii utilize the non-native alga Gracilaria vermiculophylla according to its relative refuge value. Experiments examining predation by blue crabs Callinectes sapidus on mud crabs revealed that the non-native alga had an intermediate refuge value relative to native oysters, which were the most protective, and unvegetated sediment, which was the least. In subsequent choice experiments, mud crabs selected oysters over alga over unvegetated sediment, in accordance with habitat refuge values. Further, in field experiments, the use of Gracilaria by mud crabs was inversely related to the proximity of the alga to the preferred habitat type, oysters, and was reduced by the presence of a blue crab predator. Consequently, mud crabs are utilizing the non-native alga Gracilaria in accordance with its intermediate refuge value. The relative refuge value of non-native vs native habitat-forming species may provide a baseline expectation against which to measure the speed of learning and opportunism in the response of native prey to novel protective habitats. [ABSTRACT FROM AUTHOR]

Non-native species can serve as a prey resource for native predators. Yet because there is often no shared evolutionary history between the predator and prey, individuals within a predator population may vary greatly in their willingness to consume a recently introduced, yet profitable prey. Here, we measured individual variation in diet, behavior, and demographic traits of the native predatory mud crab, Panopeus herbstii, and evaluated how these traits influenced an individual's consumption of a recently introduced, non-native crab, Petrolisthes armatus, using both simultaneous and no-choice assays. These same individual predatory mud crabs were also assayed to quantify their antipredator reaction and exploratory behavior. Results indicated significant variation in the diets of individual predators with 45% specializing on native mussels, 14% specializing on non-native Petrolisthes, and the remainder eating multiple prey species. When given a choice of alternative prey, individual Panopeus predators that consumed a larger proportion of Petrolisthes were female, smaller, and more likely to flee in response to predators. When given no choice of alternative prey, Petrolisthes was consumed more frequently by Panopeus that were female and less exploratory. We suggest that individuals that more readily consume non-native Petrolisthes may be attempting to reduce competition with conspecifics that are larger, more aggressive, exploratory, and male. Our results suggest that at least initially following invasion, adoption of a non-native prey species into the diet of a native predator may not occur universally within the population. Such nonuniform predation pressure could contribute to the nonnative prey's release from natural enemies. [ABSTRACT FROM AUTHOR]

Physical-biological coupling helps structure aquatic communities, yet physical factors can vary widely across large, biogeographic scales. The eastern oyster ( Crassostrea virginica) is an ecosystem engineer that creates intertidal reefs, filters water, promotes denitrification, stabilizes shorelines, and provides habitat throughout the inner waters of the U.S. South Atlantic Bight (SAB). We quantified physical variables (temperature, salinity, duration and depth of water inundation), oyster reef properties (slope, vertical relief), and oyster recruitment, density, and biomass over a 1500 km scale across the SAB for one year. All oyster-level and many reef-level variables exhibited unimodal patterns with latitude that peaked in Georgia and South Carolina estuaries. Of the physical variables, salinity and duration of water inundation over reefs were similar across all sites, and temperature declined linearly with increasing latitude, except during summer when it had no relationship with latitude. Depth of water inundation over reefs was the only physical variable with a prominent unimodal distribution that may explain the oyster's biological responses. Similar durations of water inundation across all reefs coupled with higher water depths in the mid-latitude sites collectively indicate that these sites experience higher flow velocity, energy and net water volume delivery per unit time. The resultant higher accumulation of oyster biomass and heightened reef structure in areas of higher tidal energy emphasize that the physical forcing of the SAB (especially large cross-shelf gradients in tidal amplification) affects the biology of the eastern oyster, including its reef properties, with potential implications for community structure and ecosystem service delivery across a biogeographic scale. [ABSTRACT FROM AUTHOR]

Nonnative species that form novel habitats strongly affect ecosystem processes. The effects of these ecosystem engineers can be both positive and negative but the mechanisms behind their effects are not well described. In this study we determined the relative importance of three main mechanisms by which invasive ecosystem engineers can facilitate native fauna. The engineer may provide new physical structure that reduces harsh abiotic conditions or gives refuge from predation (both engineering mechanisms), or provide a new profitable food resource (a trophic mechanism). The invasive seaweed Gracilaria vermiculophylla is a novel addition to estuarine intertidal mudflats of the southeastern United States. The epifaunal amphipod Gammarus mucronatus is up to 100 times more abundant on Gracilaria-invaded mudflats compared to uninvaded mudflats. Feeding assays, a survivorship experiment and stable isotope analysis demonstrated that Gammarus consumes little Gracilaria and cannot survive on Gracilaria alone. However, the structural engineering effects of Gracilaria greatly enhanced the survivorship of Gammarus in the presence of predators during high tide and when exposed to harsh abiotic conditions during low tide. Our results demonstrate that invasive ecosystem engineers can dramatically affect the distribution and abundance of native species by providing a novel protective structure. [ABSTRACT FROM AUTHOR]

Predators can indirectly benefit prey populations by suppressing mid-trophic level consumers, but often the strength and outcome of trophic cascades are uncertain. We manipulated oyster reef communities to test the generality of potential causal factors across a 1000-km region. Densities of oyster consumers were weakly influenced by predators at all sites. In contrast, consumer foraging behaviour in the presence of predators varied considerably, and these behavioural effects altered the trophic cascade across space. Variability in the behavioural cascade was linked to regional gradients in oyster recruitment to and sediment accumulation on reefs. Specifically, asynchronous gradients in these factors influenced whether the benefits of suppressed consumer foraging on oyster recruits exceeded costs of sediment accumulation resulting from decreased consumer activity. Thus, although predation on consumers remains consistent, predator influences on behaviour do not; rather, they interact with environmental gradients to cause biogeographic variability in the net strength of trophic cascades. [ABSTRACT FROM AUTHOR]

Non-native species can alter ecosystem functions performed by native species often by displacing influential native species. However, little is known about how ecosystem functions may be modified by trait-mediated indirect effects of non-native species. Oysters and other reef-associated filter feeders enhance water quality by controlling nutrients and contaminants in many estuarine environments. However, this ecosystem service may be mitigated by predation, competition, or other species interactions, especially when such interactions involve non-native species that share little evolutionary history. We assessed trophic and other interference effects on the critical ecosystem service of water filtration in mesocosm experiments. In single-species trials, typical field densities of oysters (Crassostrea virginica) reduced water-column chlorophyll a more strongly than clams (Mercenaria mercenaria). The non-native filter-feeding reef crab Petrolisthes armatus did not draw down chlorophyll a. In multi-species treatments, oysters and clams combined additively to influence chlorophyll a drawdown. Petrolisthes did not affect net filtration when added to the bivalve-only treatments. Addition of the predatory mud crab Panopeus herbstii did not influence oyster feeding rates, but it did stop chlorophyll a drawdown by clams. However, when Petrolisthes was also added in with the clams, the clams filtered at their previously unadulterated rates, possibly because Petrolisthes drew the focus of predators or habituated the clams to crab stimuli. In sum, oysters were the most influential filter feeder, and neither predators nor competitors interfered with their net effect on water-column chlorophyll. In contrast, clams filtered less, but were more sensitive to predators as well as a facilitative buffering effect of Petrolisthes, illustrating that non-native species can indirectly affect an ecosystem service by aiding the performance of a native species. [ABSTRACT FROM AUTHOR]

The evolutionary pressures that drive long larval planktonic durations in some coastal marine organisms, while allowing direct development in others, have been vigorously debated. We introduce into the argument the asymmetric dispersal of larvae by coastal currents and find that the strength of the currents helps determine which dispersal strategies are evolutionarily stable. In a spatially and temporally uniform coastal ocean of finite extent, direct development is always evolutionarily stable. For passively drifting larvae, long planktonic durations are stable when the ratio of mean to fluctuating currents is small and the rate at which larvae increase in size in the plankton is greater than the mortality rate (both in units of per time). However, larval behavior that reduces downstream larval dispersal for a given time in plankton will be selected for, consistent with widespread observations of behaviors that reduce dispersal of marine larvae. Larvae with long planktonic durations are shown to be favored not for the additional dispersal they allow, but for the additional fecundity that larval feeding in the plankton enables. We analyzed the spatial distribution of larval life histories in a large database of coastal marine benthic invertebrates and documented a link between ocean circulation and the frequency of planktotrophy in the coastal ocean. The spatial variation in the frequency of species with planktotrophic larvae is largely consistent with our theory; increases in mean currents lead to a decrease in the fraction of species with planktotrophic larvae over a broad range of temperatures. [ABSTRACT FROM AUTHOR]

Habitat-forming invasive species have complex impacts on native communities. Positive above ground and negative below ground impacts are reported, suggesting that habitat-forming invasive species may affect community components differently. Furthermore, such effects may vary depending on the density of the invader. We determined the responses of community components to different densities of the invasive green alga Caulerpa taxifolia in southeastern Australia. Initially we investigated differences in soft-sediment faunal communities (above and below ground) across a biomass gradient at two invaded sites. Caulerpa taxifolia biomass was positively associated with the composition and abundance of the epifaunal community, but negatively correlated with the abundance of infauna. To examine the response of common community members in more detail, we caged two species of mollusk (the infaunal bivalve, Anadara trapezia and the epifaunal gastropod, Batillaria australis) across the same biomass gradient to determine lethal and sublethal effects of C. taxifolia biomass on individuals. Survivorship of A. trapezia was low when C. taxifolia was above 300 g m−2. Negative sublethal effects were also density-dependent with A. trapezia tissue weight being lowest above this same C. taxifolia biomass. The proportion of B. australis surviving was unaffected by C. taxifolia biomass. However, the total number of live B. australis recovered in cages increased as C. taxifolia biomass increased, providing further evidence of positive density dependent effects (in line with the survey data) of C. taxifolia on epifauna. Finally, we removed C. taxifolia from plots of differing C. taxifolia biomass and followed community change for 5 months. Community change following C. taxifolia removal was also density dependent as recovery 5 months post-removal depended on the initial biomass of C. taxifolia, suggesting a lag in the recovery of communities due to residual environmental effects post-removal (i.e. hysteresis). We have shown that the effects of a habitat-forming invasive species are biomass dependent and also affect community components differently, suggesting that, globally, the impact of these types of invaders may be context dependent. [ABSTRACT FROM AUTHOR]

Predicting the potential range of invasive species is essential for risk assessment, monitoring, and management, and it can also inform us about a species’ overall potential invasiveness. However, modeling the distribution of invasive species that have not reached their equilibrium distribution can be problematic for many predictive approaches. We apply the modeling approach of maximum entropy (MaxEnt) that is effective with incomplete, presence-only datasets to predict the distribution of the invasive island apple snail, Pomacea insularum. This freshwater snail is native to South America and has been spreading in the USA over the last decade from its initial introductions in Texas and Florida. It has now been documented throughout eight southeastern states. The snail’s extensive consumption of aquatic vegetation and ability to accumulate and transmit algal toxins through the food web heighten concerns about its spread. Our model shows that under current climate conditions the snail should remain mostly confined to the coastal plain of the southeastern USA where it is limited by minimum temperature in the coldest month and precipitation in the warmest quarter. Furthermore, low pH waters (pH <5.5) are detrimental to the snail’s survival and persistence. Of particular note are low-pH blackwater swamps, especially Okefenokee Swamp in southern Georgia (with a pH below 4 in many areas), which are predicted to preclude the snail’s establishment even though many of these areas are well matched climatically. Our results elucidate the factors that affect the regional distribution of P. insularum, while simultaneously presenting a spatial basis for the prediction of its future spread. Furthermore, the model for this species exemplifies that combining climatic and habitat variables is a powerful way to model distributions of invasive species. [ABSTRACT FROM AUTHOR]

Co-occurring foundation species can determine biological community structure via facilitation cascades. We examined the density dependencies of facilitation cascades, including how the density of a basal foundation species influences the density of secondary foundation species, and how the density of secondary foundation species influences community structure. The system in which we assessed density dependencies was a temperate mangrove forest in which pneumatophores trap the fucoid alga Hormosira banksii and provide substrate for the oyster, Saccostrea glomerata. The alga and oyster in turn determine benthic community structure. In the field, algal biomass was positively correlated with pneumatophore density. Oysters, by contrast, were highly over-dispersed and correlated with the presence/ absence of pneumatophores. Epifaunal abundance and species richness were positively correlated with algal and oyster abundance, but their effects were independent. The positive effect of pneumatophore density on epifauna was primarily an indirect effect of trapping more algae. Pneumatophores did not directly influence invertebrate communities. Experiments revealed that, at very low pneumatophore densities, algal retention was insufficient to facilitate epifauna above that found on pneumatophores alone. At higher densities, however, increasing the density of pneumatophores increased algal retention, and the density and diversity of associated invertebrates. Shading by the mangrove canopy reduced algal biomass but did not modify the density-dependent nature of the cascade. Our results extend facilitation theory by showing that the density of both basal and secondary foundation species can be critical in triggering facilitation cascades. Our study also reveals that, where foundation species co-occur, multiple, independent cascades may arise from a single basal facilitator. These findings enhance our understanding of the role of density-dependent facilitation cascades in community assembly. [ABSTRACT FROM AUTHOR]

Utilizing marine protected areas (MPAs) to isolate the ecological effects of human influence can help us understand our effect on systems and foster ecosystem-based approaches to management. Specifically, examining invertebrate prey community dynamics inside and outside an MPA may provide a measure of how altering human influence (i.e., certain fishing pressures) affects ecosystem interactions. We measured trophic interactions inside and outside a deep-water temperate MPA over 2 years. Predation rates on tethered, preferred groundfish prey (crabs) were initially identical inside and outside the MPA, but decreased outside the MPA after the commercial groundfish fishing season commenced. Predation trials using a ubiquitous prey species (brittle stars) and a less preferred prey species (urchins) served as controls, showing no MPA effect. Our experiments quantify differential predatory activity resulting from differences in human activity driven by an MPA, demonstrating important effects of fishing and regulations on the strength of trophic interactions. [ABSTRACT FROM AUTHOR]

Digenean trematode parasites require multiple host species to complete their life cycles, and their abundance can often be strongly correlated with the abundance of their host species. Species richness and abundance of parasites in easily sampled host species may yield an accurate estimate of the species richness and abundance of other hosts in a parasite's life cycle that are difficult to survey directly. Accordingly, we investigated whether prevalence and mean abundance of trematodes could be used to estimate the abundance of one of their host species, diamondback terrapins (Malaclemys terrapin ), which are difficult to sample and are designated as near threatened (by the International Union for Conservation of Nature [IUCN Red List]) along some U.S. coasts. As an adult the trematode Pleurogonius malaclemys is specific to terrapins. Its larval stages live first inside mud snails (Ilyanassa obsoleta ) and are subsequently shed into the environment where they form external metacercarial cysts on hard surfaces such as snail opercula. The life cycle of P. malaclemys is completed when terrapins ingest these cysts. At 12 sites along the coast of Georgia (U.S.A.), we determined the prevalence of internal P. malaclemys larvae in mud snails (proportion of infected snails in a population) and the prevalence and mean abundance of external trematode cysts. We examined whether these data were correlated with terrapin abundance, which we estimated with mark-recapture methods. The abundance of external cysts and salinity explained ≥59% of the variability in terrapin abundance. We suggest that dependent linkages between the life stages of multihost parasites make them reliable predictors of host species' abundance, including hosts with abundances that are challenging to quantify directly. [ABSTRACT FROM AUTHOR]

Habitat-modifying invasive species can influence rates of predation on native prey either directly by providing protective structure or indirectly by modifying traits of prey species responding to the habitat. The alga Caulerpa taxifolia is one of the most successful invasive species of shallow-water marine systems globally, often provisioning habitat in areas previously lacking in vegetated structure. We experimentally evaluated the direct effect of Caulerpa to provide refuge for the native clam Anadara trapezia and how this balances with its influence on two trait-mediated indirect interactions that may increase Anadara's susceptibility to predators. Specifically, Caulerpa's alteration of physical and chemical properties of the surrounding water and sediment deteriorate Anadara's condition and predator resistance properties and also cause Anadara, though normally buried, to project from beneath the sediment, exposing it to predators. Our results show that Anadara are somewhat (but not consistently) protected from predators by living among Caulerpa. Shallow burial depth did not counteract this protective effect. However at times of year when predator activity diminishes and conducive environmental conditions develop, negative effects of Caulerpa habitat such as hypoxia and lowered flow may dominate. Under such situations, poor clam condition accentuates Anadara's susceptibility to mortality. Ultimately, a slight and inconsistent positive effect of Caulerpa to protect Anadara from predators is exceeded by the strong negative effect of Caulerpa on clam mortality, which is heightened by clams' weakened condition produced by chronic exposure to Caulerpa. Our results show that invasive habitat-modifying species can affect mortality of native species not simply through obvious positive direct effects of their protective structure, but indirectly through contrasting negative modification of the traits of prey species responding to the habitat. [ABSTRACT FROM AUTHOR]

Habitat-forming invasive species cause large, novel changes to the abiotic environment. These changes may elicit important behavioural responses in native fauna, yet little is known about mechanisms driving this behaviour and how such trait-mediated responses influence the fitness of native species. Low dissolved oxygen is a key abiotic change created by the habitat-forming invasive seaweed, Caulerpa taxifolia, which influences an important behavioural response (burrowing depth) in the native infaunal bivalve Anadara trapezia. In Caulerpa-colonised areas, Anadara often emerged completely from the sediment, and we experimentally demonstrate that water column hypoxia beneath the Caulerpa canopy is the mechanism instigating this “pop-up” behaviour. Importantly, pop-up in Caulerpa allowed similar survivorship to that in unvegetated sediment; however, when we prevented Anadara from popping-up, they suffered >50% mortality in just 1 month. Our findings not only highlight the substantial environmental alteration by Caulerpa, but also an important role for the behaviour of native species in mitigating the effects of habitat-forming invasive species. [ABSTRACT FROM AUTHOR]

Behavioural interactions between ecosystem engineers may strongly influence community structure. We tested whether an invasive ecosystem engineer, the alga Caulerpa taxifolia, indirectly facilitated community diversity by modifying the behaviour of a native ecosystem engineer, the clam Anadara trapezia, in southeastern Australia . In this study, clams in Caulerpa-invaded sediments partially unburied themselves, extending >30% of their shell surface above the sediment, providing rare, hard substrata for colonization. Consequently, clams in Caulerpa had significantly higher diversity and abundance of epibiota compared with clams in unvegetated sediments. To isolate the role of clam burial depth from direct habitat influences or differential predation by habitat, we manipulated clam burial depth, predator exposure and habitat ( Caulerpa or unvegetated) in an orthogonal experiment. Burial depth overwhelmingly influenced epibiont species richness and abundance, resulting in a behaviourally mediated facilitation cascade. That Caulerpa controls epibiont communities by altering Anadara burial depths illustrates that even subtle behavioural responses of one ecosystem engineer to another can drive extensive community-wide facilitation. [ABSTRACT FROM AUTHOR]

Even after decades of investigation using multiple sources of evidence, the natural histories of some species remain unclear (i.e. cryptogenic). A key example is Littorina littorea, the most abundant intertidal snail in northeastern North America. Native to Europe, the snail's ecological history in North America has been debated for over 100 years with no definitive resolution. To resolve its cryptogenic status, we used molecular genetics from a novel combination of the snail and a highly associated trematode parasite, Cryptocotyle lingua. Based on mitochondrial sequences of 370 L. littorea and 196 C. lingua individuals, our results demonstrate a significant reduction in genetic diversity in North America vs. Europe, North American haplotypes nested within European haplotypes, and mean divergence estimates of ~500 years ago from Europe for both host and parasite — thus supporting a recent introduction of both host and parasite to North America from Europe. Our study therefore resolves not only a specific cryptogenic history, but it also demonstrates the success of our approach generally and could be used in resolving difficult invasion histories worldwide. [ABSTRACT FROM AUTHOR]

Scientific and societal unknowns make it difficult to predict how global environmental changes such as climate change and biological invasions will affect ecological systems. In the long term, these changes may have interacting effects and compound the uncertainty associated with each individual driver. Nonetheless, invasive species are likely to respond in ways that should be qualitatively predictable, and some of these responses will be distinct from those of native counterparts. We used the stages of invasion known as the “invasion pathway” to identify 5 nonexclusive consequences of climate change for invasive species: (1) altered transport and introduction mechanisms, (2) establishment of new invasive species, (3) altered impact of existing invasive species, (4) altered distribution of existing invasive species, and (5) altered effectiveness of control strategies. We then used these consequences to identify testable hypotheses about the responses of invasive species to climate change and provide suggestions for invasive-species management plans. The 5 consequences also emphasize the need for enhanced environmental monitoring and expanded coordination among entities involved in invasive-species management. [ABSTRACT FROM AUTHOR]

Species introduced to novel regions often leave behind many parasite species. Signatures of parasite release could thus be used to resolve cryptogenic (uncertain) origins such as that of Littorina littorea, a European marine snail whose history in North America has been debated for over 100 years. Through extensive field and literature surveys, we examined species richness of parasitic trematodes infecting this snail and two co-occurring congeners, L. saxatilis and L. obtusata, both considered native throughout the North Atlantic. Of the three snails, only L. littorea possessed significantly fewer trematode species in North America, and all North American trematodes infecting the three Littorina spp. were a nested subset of Europe. Surprisingly, several of L. littorea's missing trematodes in North America infected the other Littorina congeners. Most likely, long separation of these trematodes from their former host resulted in divergence of the parasites' recognition of L. littorea. Overall, these patterns of parasitism suggest a recent invasion from Europe to North America for L. littorea and an older, natural expansion from Europe to North America for L. saxatilis and L. obtusata. [ABSTRACT FROM AUTHOR]

Geographic variability in abundance can be driven by multiple physical and biological factors operating at multiple scales. To understand the determinants of larval trematode prevalence within populations of the marine snail host Littorina littorea, we quantified many physical and biological variables at 28 New England intertidal sites. A hierarchical, mixed-effects model identified the abundance of gulls (the final hosts and dispersive agents of infective trematode stages) and snail size (a proxy for time of exposure) as the primary factors associated with trematode prevalence. The predominant influence of these variables coupled with routinely low infection rates (21 of the 28 populations exhibited prevalence <12%) suggest broad-scale recruitment limitation of trematodes. Although infection rates were spatially variable, formal analyses detected no regional spatial gradients in either trematode prevalence or independent environmental variables. Trematode prevalence appears to be predominantly determined by local site characteristics favoring high gull abundance. [ABSTRACT FROM AUTHOR]

Parasites often play an important role in modifying the physiology and behavior of their hosts and may, consequently, mediate the influence hosts have on other components of an ecological community. Along the northern Atlantic coast of North America, the dominant herbivorous snail Littorina littorea structures rocky intertidal communities through strong grazing pressure and is frequently parasitized by the digenean trematode Cryptocotyle lingua. We hypothesized that the effects of parasitism on host physiology would induce behavioral changes in L. littorea, which in turn would modulate L. littorea's influence on intertidal community composition. Specifically, we hypothesized that C. lingua infection would alter the grazing rate of L. littorea and, consequently, macroalgal communities would develop differently in the presence of infected versus uninfected snails. Our results show that uninfected snails consumed 40% more ephemeral macroalgal biomass than infected snails in the laboratory, probably because the digestive system of infected snails is compromised by C. lingua infection. In the field, this weaker grazing by infected snails resulted in significantly greater expansion of ephemeral macroalgal cover relative to grazing by uninfected snails. By decreasing the per-capita grazing rate of the dominant herbivore, C. lingua indirectly affects the composition of the macroalgal community and may in turn affect other species that depend on macroalgae for resources or habitat structure. In light of the abundance of parasites across systems, we suggest that, through trait-mediated indirect effects, parasites may be a common determinant of structure in ecological communities. [ABSTRACT FROM AUTHOR]

Abstract: Exotic species are prominent constituents of fouling communities. If exotic fouling organisms colonize or compete better on a wider range of substrate types than native species, this may partially account for their high abundance in estuaries and bays. We used four artificial and four naturally occurring substrate types to compare initial settlement and percent cover of native and exotic fouling species through six months of community development. Both the identity of common taxa and the total number of species colonizing artificial versus natural substrate types were similar. Despite the similarities in species richness, relative abundance patterns between natural and artificial substrate types varied, particularly as the communities developed. Native species were initially in equal abundance on natural and artificial substrate types. Initially, the two most common exotic species, the colonial tunicates, Botrylloides violaceus Ritter and Forsyth and Botryllus schlosseri (Pallas), were also in similar, but low, abundance on artificial and natural substrates. As the communities developed, there was little change in abundance of exotic or native species on natural substrates. However, on artificial substrates the exotic tunicates increased dramatically and native species declined in abundance. Artificial surfaces may provide a novel context for competitive interactions giving exotic species a more “level playing field” in an environment for which they otherwise might not be as well adapted compared to long-resident native species. Additions of artificial substrates to nearshore environments may disproportionately favor exotic species by increasing local sources of exotic propagules to colonize all types of substrates. [Copyright &y& Elsevier]

The ecosystem engineering concept focuses on how organisms physically change the abiotic environment and how this feeds back to the biota. While the concept was formally introduced a little more than 10 years ago, the underpinning of the concept can be traced back to more than a century to the early work of Darwin. The formal application of the idea is yielding new insights into the role of species in ecosystems and many other areas of basic and applied ecology. Here we focus on how temporal, spatial and organizational scales usefully inform the roles played by ecosystem engineers and their incorporation into broader ecological contexts. Two particular, distinguishing features of ecosystem engineers are that they affect the physical space in which other species live and their direct effects can last longer than the lifetime of the organism – engineering can in essence outlive the engineer. Together, these factors identify critical considerations that need to be included in models, experimental and observational work. The ecosystem engineering concept holds particular promise in the area of ecological applications, where influence over abiotic variables and their consequent effects on biotic communities may facilitate ecological restoration and counterbalance anthropogenic influences. [ABSTRACT FROM AUTHOR]

Ecosystem engineers affect other organisms by creating, modifying, maintaining or destroying habitats. Despite widespread recognition of these often important effects, the ecosystem engineering concept has yet to be widely used in ecological applications. Here, we present a conceptual framework that shows how consideration of ecosystem engineers can be used to assess the likelihood of restoration of a system to a desired state, the type of changes necessary for successful restoration and how restoration efforts can be most effectively partitioned between direct human intervention and natural ecosystem engineers. [Copyright &y& Elsevier]

1. Interference between predator species frequently decreases predation rates, lowering the risk of predation for shared prey. However, such interference can also occur between conspecific predators. 2. Therefore, to understand the importance of predator biodiversity and the degree that predator species can be considered functionally interchangeable, we determined the degree of additivity and redundancy of predators in multiple- and single-species combinations. 3. We show that interference between two invasive species of predatory crabs, Carcinus maenas and Hemigrapsus sanguineus, reduced the risk of predation for shared amphipod prey, and had redundant per capita effects in most multiple- and single-species predator combinations. 4. However, when predator combinations with the potential for intraguild predation were examined, predator interference increased and predator redundancy decreased. 5. Our study indicates that trophic structure is important in determining how the effects of predator species combine and demonstrates the utility of determining the redundancy, as well as the additivity, of multiple predator species. [ABSTRACT FROM AUTHOR]

Prey are often consumed by multiple predator species. Predation rates on shared prey species measured in isolation often do not combine additively due to interference or facilitation among the predator species. Furthermore, the strength of predator interactions and resulting prey mortality may change with habitat type. We experimentally examined predation on amphipods in rock and algal habitats by two species of intertidal crabs, Hemigrapsus sanguineus (top predators) and Carcinus maenas (intermediate predators). Algae provided a safer habitat for amphipods when they were exposed to only a single predator species. When both predator species were present, mortality of amphipods was less than additive in both habitats. However, amphipod mortality was reduced more in rock than algal habitat because intermediate predators were less protected in rock habitat and were increasingly targeted by omnivorous top predators. We found that prey mortality in general was reduced by (1) altered foraging behavior of intermediate predators in the presence of top predators, (2) top predators switching to foraging on intermediate predators rather than shared prey, and (3) density reduction of intermediate predators. The relative importance of these three mechanisms was the same in both habitats; however, the magnitude of each was greater in rock habitat. Our study demonstrates that the strength of specific mechanisms of interference between top and intermediate predators can be quantified but cautions that these results may be habitat specific. [ABSTRACT FROM AUTHOR]

Invasion biologists typically regard susceptibility of an invasive species to native predators as a fortuitous condition that increases biotic resistance to the invasion. The line of reasoning is that predation weakens the net impact of the invader and reduces its ability to displace native competitors. However, predation on invasives is a coupled interaction; every invader consumed also enhances the predator population. If these predators also consume native species, then the invader's indirect effect via predators (i.e., apparent competition) could be more harmful to natives than the effect of resource competition from the exotic. We apply general community ecology theory to determine the conditions under which the net effect of predation on the exotic species is to extirpate the native competitor An approximation to these conditions provides a simple metric to estimate the threat of native species extinction due to apparent competition posed by an invader. [ABSTRACT FROM AUTHOR]

Marine reserves are being increasingly used to protect exploited marine species. However, blanket protection of species within a reserve may shelter nonindigenous species that are normally affected by harvesting, intensifying their impacts on native species. I studied a system of marine reserves in the San Juan Islands, Washington, USA, to examine the extent to which marine reserves are invaded by nonindigenous species and the consequences of these invasions on native species. I surveyed three reserves and eight non-reserves to quantify the abundance of intertidal suspension-feeding clam species, three of which are regionally widespread nonindigenous species (Nuttallia obscurata, Mya arenaria, and Venerupis philippinarum). Neither total nonindigenous nor native species' abundance was significantly greater on reserves. However, the most heavily harvested species, V. philippinarum, was significantly more abundant on reserves, with the three reserves ranking highest in Venerupis biomass of all 11 sites. In contrast, a similar, harvested native species (Protothaca staminea) did not differ between reserves and non-reserves. I followed these surveys with a year-long field experiment replicated at six sites (the three reserves and three of the surveyed non-reserve sites). The experiment examined the effects of high Venerupis densities on mortality, growth, and fecundity of the confamilial Protothaca, and whether differences in predator abundance mitigate density-dependent effects. Even at densities 50% higher than measured in the field survey, Venerupis had no direct effect on itself or Protothaca; only site, predator exposure, and their interaction had significant effects. Analyses incorporating environmental variables tracked at each site indicated that crab biomass most heavily influenced clam responses, causing lower growth of both species and higher mortality of Venerupis, whose annualized loss rate was 50% when exposed to predators. A laboratory prey choice experiment indicated that Cancer productus, an influential intertidal crab predator, favored small adult Venerupis at least I .7 times over Protothaca. Venerupis' high susceptibility to excavating crab and human pred- atorst as well as its faster growth compared to Protothaca can be explained by its shallower burial depth. By growing quickly and residing near the surface, Venerupis apparently absorbs the brunt of harvest pressure while Protothaca maintains high biomass even outside of reserves. [ABSTRACT FROM AUTHOR]

Although ecologists have speculated that sublethal predation can impact prey dynamics, consequences of these predator effects have seldom been experimentally tested. In soft-sediment marine communities, fishes crop extended feeding siphons of buried clams, potentially causing clams to reduce their burial depth, thereby enhancing their susceptibility to excavating lethal predators. We simulated cropping of the confamilial clams,Protothaca stamineaandVenerupis philippinarum, by removing the top 40% of siphons, which caused each species to burrow 33–50% shallower than conspecifics with intact siphons. To examine subsequent consequences of reduced burial depth, we exposed cropped and intact clams to natural levels of predation in the field. Because of a naturally longer siphon,Protothaca, even after cropping, remained at relatively safe burial depths. In contrast, siphon cropping nearly doubled the mortality rate ofVenerupis. Thus, while sublethal predation facilitates lethal predation, this linkage depends on specific life history characteristics, even among ecologically similar species. [ABSTRACT FROM AUTHOR]

As non-indigenous species continue to displace native species and disrupt ecosystems, understanding the degree to which native species richness affects the vulnerability of communities to non-indigenous species invasions has grown in importance. Native and exotic species diversity are often positively correlated in large-scale observational studies, but negatively correlated in small-scale experimental studies. This discrepancy suggests that the scale of invasion studies may be an important influence on their outcomes. Using a competition-based model that exhibits a negative relationship on a small scale, we show that changes in the number of available resources across communities can cause invasion success to become positively correlated with native species diversity at larger scales. The strength of the positive correlation, however, depends on the relationship between niche breadth and species diversity in natural communities. Adding species to a community or removing resources has a similar effect—increasing the sum of interspecific interaction strengths, which decreases invasion success. [ABSTRACT FROM AUTHOR]

Investigates the impact of non-indigenous species on natives enhanced by anthropogenic alteration of selection regimes. Effect of changes in environmental conditions on interactions among species; Disadvantages for non-native species; Implications of biological invasions in globally disturbed biosphere.

Management of nonindigenous species is a crucial aspect of maintaining native biodiversity and normal ecosystem functions. We attempt to guide researchers in developing projects that will be of use to conservation practitioners, tangibly improving applied conservation measures. We advocate a directed approach for conservation research to aid in prioritizing nonindigenous species for intervention by resource managers. This approach includes outlining what needs to be known to make such relative judgments about the impacts of nonindigenous species and the most promising methods by which to obtain such information. We also address active measures that should be taken once priorities have been set, highlighting the roles of risk assessment and research in improving control efforts. Ultimately, a better match between research and practical conservation needs should result in more effective reduction of the effects of nonindigenous species on native species. [ABSTRACT FROM AUTHOR]

Examines the impact of Batillaria attramentaria's invasion on native species, Caerithidea californica's population density, biomass, egg production, mean size, growth rate and availability of shared food resources. Effects of B. attramentaria invasion on probability of extinction of C. californica; Analysis of synergistic effect between competition and parasitism.

Examines biotic competition between the introduced snail Batillaria attramentaria and native mud snail Cerithidea californica in the salt marshes and mud flats in California. Effects of food resource on snails; Impact of intraspecific competition on the relative growth rates of both species; Determination of the growth responses of snails to diatom densities.

Although parasites can kill their hosts, they also commonly cause nonlethal effects on their hosts, such as altered behaviors or feeding rates. Both the lethal and nonlethal effects of parasites can influence host resource consumption. However, few studies have explicitly examined the joint lethal and nonlethal effects of parasites to understand the net impacts of parasitism on host resource consumption. To do this, we adapted equations used in the indirect effects literature to quantify how parasites jointly influence basal resource consumption through nonlethal effects (altered host feeding rate) and lethal effects (increased host mortality). To parametrize these equations and to examine the potential temperature sensitivity of parasite influences, we conducted a fully factorial lab experiment (crossing trematode infection status and a range of temperatures) to quantify feeding rates and survivorship curves of snail hosts. We found that infected snails had significantly higher mortality and ate nearly twice as much as uninfected snails and had significantly higher mortality, resulting in negative lethal effects and positive nonlethal effects of trematodes on host resource consumption. The net effects of parasites on resource consumption were overall positive in this system, but did vary with temperature and experimental duration, highlighting the context dependency of outcomes for the host and ecosystem. Our work demonstrates the importance of jointly investigating lethal and nonlethal effects of parasites and provides a novel framework for doing so. [ABSTRACT FROM AUTHOR]