Size Refuge Research Articles

Lobster predation on barren-forming sea urchins is more prevalent in habitats where small urchins are common: a multi-method diet analysis

Context In Tasmania, Australia, the government’s response to range-extending, barren-forming longspined sea urchin (Centrostephanus rodgersii) includes rebuilding of southern rock lobster (Jasus edwardsii) stocks to increase predation. But lobster preference for native species and continued barren expansion challenges the control efficacy. Aims To determine the impact of lobster predation on C. rodgersii in different habitats. Methods Multi-method dietary analysis consisting of stomach contents, faecal DNA and stable isotopes was performed on 64 lobsters from four habitats varying in barren extent and density of urchins and lobsters. Key results C. rodgersii contributed to lobster diet in all barren habitats and was found in lobsters of every size class. Stable isotope and DNA analyses showed that C. rodgersii was more common in lobster diet than were targeted native species at incipient barren sites. Surprisingly, in extensive barrens C. rodgersii is less prominent in lobster diet. Conclusions Combined with site-specific urchin population data, our findings indicated that lobster predation may be less effective at sites where most C. rodgersii individuals have reached a size refuge than at sites dominated by small urchins. Implications Lobster predation may provide a useful control for smaller C. rodgersii, but top–down predatory control may be constrained at sites dominated by urchins that exceed the size suitable for lobster predation.

Evidence of biotic interactions through shell repair on Early Cretaceous gastropods from west-central Argentina

Evidence of durophagous predatory behavior on benthic invertebrates in the Upper Jurassic–Lower Cretaceous of the Neuquén Basin is scarce, despite the abundant record of potential predators. Herein, we document shell repair in one gastropod from lower Barremian marginal-marine deposits in northern Neuquén Basin, Argentina. This is the first report of shell repair on Early Cretaceous gastropods from Argentina and of shell repair frequencies from the Lower Cretaceous. Paleoanculosa macrochilinoides shells from three sections of the La Tosca Member (Huitrín Formation) in Mendoza province were studied. We described and interpreted the repaired breakage, calculated repair frequencies which were compared among localities, tested for geographic differences in size distribution of total samples and of repaired vs. undamaged shells, and assessed whether this species reached a size refuge. Studied shell repair consists of fractures cutting through growth lines roughly diagonally, from suture to suture, and near the aperture, thus representing apertural damage. Given its stereotypical nature, the damage represents the record of a biotic interaction, likely sublethal predation, instead of diagenetic compaction or damage by physical disturbance. Repair frequencies are low, indicating that shell architecture made P. macrochilinoides susceptible to lethal predatory attacks, or else that there were few predator-prey encounters. There are no major geographic differences regarding repair frequency, size distribution, and preservation. Likely, P. macrochilinoides did not reach a size refuge. This study provides evidence from both a time slice and geographic area with scarce data on crushing predation and from an in-between phase within the Mesozoic Marine Revolution.

Droughts Reduce Growth Rates and Increase Vulnerability to Increasingly Frequent and Severe Drying Events in an Aquatic Ectotherm

Many aquatic organisms are experiencing increasingly severe and frequent droughts and drying events. Simultaneously, drought effects are carrying over to nondrought years as ecosystems remain in incomplete states of recovery. Aquatic organisms are thus faced with fewer sequential years under degraded environmental conditions to prepare for increasingly severe droughts and potential drying events. We assessed the effect of droughts and sex on the growth, mass, and mass-dependent estivation potential of long-lived aquatic salamanders (Greater Sirens, Siren lacertina) that estivate during drying events brought on by severe droughts. We calculated growth rates of S. lacertina based on mark–recapture data spanning 11 yr of a severe drought local minimum (of past 50 yr) in the southeastern United States. Sirens showed a distinct seasonal gain in body length and mass from March through September and little growth for the rest of the year. Gains during the growth season were strongly reduced by drought conditions. Although male and female sirens were predicted to reach a similar maximum body size, females grew much slower. Recruitment into drying event “size refugia” is constrained by drying event severity (determines minimum size required), frequency (determines available time between events to grow), and environmental conditions between drying events (determines the rate of growth). Thus, increases in drying event severity and frequency will require faster growth to a larger body size for successful recruitment into a size class that is resistant to drying events. The slower growth of females and reduction of growth during suboptimal years (mild to moderate droughts) suggest that the life history strategy of Greater Sirens for persisting through drying events potentially increases their demographic susceptibility to the predicted effects of climate change.

Predation of the crab Acanthocyclus albatrossis on seeds of the bivalve Mytilus chilensis under different environmental conditions: Importance of prey and predator size

Predation is one of the most important interactions in biology, playing a fundamental role in the ecology of populations and communities. In southern Chile, the mussel Mytilus chilensis supports a large aquaculture industry. This species cohabits with one of its predators, the crab Acanthocyclus albatrossis, both in wild bivalve beds and in suspended culture systems. In this investigation, we assessed the predator-prey interaction between these two species, addressing the following aspects: a) the vulnerability pattern of M. chilensis to predation by A. albatrossis; b) prey sizes that are free of predation (the refuge in size); c) the attack rate and d) the effects of temperature and salinity on predation by different-sized A. albatrossis crabs. The prey sizes most likely to be attacked were 7.5, 12 and 14 mm (valve length) respectively for the three predator size categories evaluated. The sizes of the mussels that are free of predation were > 12, > 18 and > 22 mm respectively for each predator size. The mean attack rate was affected by the size of M. chilensis, with the smallest prey (6–12 mm) exposed the highest predation pressure. Temperature exhibited a positive linear effect on the median attack rate only for crabs in the smallest size category; no pattern was observed for the effect of temperature on the other sizes of crabs. Salinity showed no evident effects on the median attack rate at any size category. Our results indicate that A. albatrossis could be an important predator of M. chilensis recruits in wild bivalve beds, and of seeds in suspended culture systems.

Growth, developmental, and size structure responses in tadpole prey under increasing threat from gape-limited newts

Size variability within a cohort can have profound effects on community ecology and evolution. Although competition for resources generally increases size variability, the effect of (non-consumptive) predation on this demographic trait remains relatively poorly understood. Existing models suggest a positive correlation between growth rate (mediated by resource level) and expression of size variability (as measured by the coefficient of variation) in prey cohorts. We tested this prediction by exposing the tadpoles of the Japanese Forest Green Treefrog (Rhacophorus arboreus (Okada and Kawano, 1924) = Zhangixalus arboreus (Okada and Kawano, 1924)) to the non-lethal presence of gape-limited Japanese Fire-bellied Newts (Cynops pyrrhogaster (Boie, 1826)) at low and high predator densities in an outdoor mesocosm experiment. Tadpole growth rates and periphyton biomass increased with newt density. But in contrast to prediction, elevated growth rates did not increase but, reversely, decreased cohort size variability in the tadpoles. We discuss two potential mechanisms behind this outcome. First, increased resource availability mediated by predator feeding may have reduced the strength of competition, ultimately leading to more evenly distributed resource gains among individuals; second, if smaller individuals grew relatively faster than larger individuals, as to quicken entry to a size refuge against the gape-limited predator, then inter-individual size differences could diminish over time.

Eastern oysters use predation risk cues in larval settlement decisions and juvenile inducible morphological defenses

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 621:83-94 (2019) - DOI: https://doi.org/10.3354/meps12998 Eastern oysters use predation risk cues in larval settlement decisions and juvenile inducible morphological defenses Jessica L. Pruett*, Marc J. Weissburg School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA 30332, USA *Corresponding author: jpruett7@gatech.edu ABSTRACT: Predation is an important factor affecting the recruitment of marine benthic populations. Larvae can reduce their risk of predation by avoiding settlement near predators, whereas juveniles can resist predation through induced morphological defenses. We performed a 2 mo field study to understand the nature of the predation risk cues used by settling eastern oyster larvae and developing juveniles to decrease predation threat during recruitment. We found that oyster recruitment was highest on caged tiles near juvenile oysters, but lowest on tiles near active mud crab predators that produce a combination of predator metabolites and crushed conspecific alarm cues. Chemical cues from crushed conspecifics alone did not affect recruitment in the field, yet oyster larvae avoided either mud crab cues or crushed conspecific cues when presented separately in lab behavior experiments. Comparing the field to lab results suggests alarm cues may be unreliable under natural environmental conditions or were not present at high enough concentrations in the relatively high turbulent flow environment of our field site to convey the predation threat necessary to deter oyster settlement. Oyster spat grew most quickly when exposed to crushed conspecifics and may employ different strategies in response to unique risk cues or predation risk levels by avoiding settlement near actively feeding future predators but growing quickly to reach a size refuge in the presence of alarm cues. These non-consumptive predator effects at different life stages may have important demographic consequences for oyster populations that need to be considered in conjunction with predator consumptive effects. KEY WORDS: Alarm cue · Crassostrea virginica · Non-consumptive effect · Panopeus herbstii · Phenotypic plasticity · Predation risk · Settlement cue Full text in pdf format PreviousNextCite this article as: Pruett JL, Weissburg MJ (2019) Eastern oysters use predation risk cues in larval settlement decisions and juvenile inducible morphological defenses. Mar Ecol Prog Ser 621:83-94. https://doi.org/10.3354/meps12998 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 621. Online publication date: July 04, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Predicting the contributions of novel marine prey resources from angling and anadromy to the diet of a freshwater apex predator

Abstract Anadromous fishes can be important prey resources for piscivorous fauna in lowland rivers. Freshwater anglers exploiting large‐bodied cypriniform fishes use high quantities of pelletised marine fishmeal baits that can contribute substantially to fish diets. This marine‐derived energy pathway also potentially provides a marine prey resource for freshwater piscivores. However, large‐bodied cypriniform fishes are often in a size refuge against predation due to their large sizes. Stable isotope (δ15N and δ13C) analysis assessed how novel marine prey resources influenced the diet of a freshwater apex predator, northern pike Esox lucius, in an impounded river basin (lower River Severn, western England). Up to three groups of prey resources were present: anadromous European shad (Alosa spp.), cypriniform fishes with dietary specialisms based on marine fishmeal baits, and freshwater prey. The availability of these prey resources to E. lucius varied according to river connectivity and levels of angling exploitation in different river reaches. Where the three prey groups were present, E. lucius were more enriched in δ13C values (range: −24.74 to −16.34‰) compared to river reaches where aspects of the marine prey groups were absent (range: −28.30 to −21.47). In all reaches, δ13C increased as E. lucius length increased. In the reach where all prey groups were present, the isotopic niches of three E. lucius size categories were strongly partitioned; this was not apparent in reaches where the marine pathways were unavailable. Stable isotope mixing models suggested that freshwater prey were the most important prey item, contributing between 42% and 96% to the diet of individual E. lucius. However, where present, anadromous fishes and cypriniform fishes specialising on marine fishmeal baits were also important prey items, contributing substantially to the diet of larger E. lucius (length > 650 mm). The total dietary contributions of the marine resources varied considerably among the individual larger fish (22–58% of total diet). The presence of two marine resource pathways in a lowland river thus strongly influenced the diet of an apex predator, but with contributions being a function of their spatial availability, E. lucius body size and individual trophic specialisations. These results emphasise how the anthropogenic activities of river engineering and human subsidies can affect the trophic dynamics of apex predators.

Size-dependent locomotory performance creates a behaviorally mediated prey size refuge in the marine snail Olivella semistriata: a study in the natural habitat.

The effects of the variability of individual prey locomotory performance on the vulnerability to predation are poorly understood, partly because individual performance is difficult to determine in natural habitats. To gain insights into the role(s) of individual variation in predatory relationships, we study a convenient model system, the neotropical sandy beach gastropod Olivella semistriata and its main predator, the carnivorous snail Agaronia propatula. The largest size class of O. semistriata is known to be missing from A. propatula’s spectrum of subdued prey, although the predator regularly captures much larger individuals of other taxa. To resolve this conundrum, we analyzed predation attempts in the wild. While A. propatula attacked O. semistriata of all sizes, large prey specimens usually escaped by ‘sculling’, an accelerated, stepping mode of locomotion. Olivella semistriata performed sculling locomotion regardless of size, but sculling velocities determined in the natural environment increased strongly with size. Thus, growth in size as such does not establish a prey size refuge in which O. semistriata is safe from predation. Rather, a behaviorally mediated size refuge is created through the size-dependence of sculling performance. Taken together, this work presents a rare quantitative characterization in the natural habitat of the causal sequence from the size-dependence of individual performance, to the prey size-dependent outcome of predation attempts, to the size bias in the predator’s prey spectrum.

Differential Interaction Strengths and Prey Preferences Across Larval Mosquito Ontogeny by a Cohabiting Predatory Midge.

Understandings of natural enemy efficacy are reliant on robust quantifications of interaction strengths under context-dependencies. For medically important mosquitoes, rapid growth during aquatic larval stages could impede natural enemy impacts through size refuge effects. The identification of biocontrol agents which are unimpeded by ontogenic size variability of prey is therefore vital. We use functional response and prey preference experiments to examine the interaction strengths and selectivity traits of larvae of the cohabiting predatory midge Chaoborus flavicans (Meigen 1830) (Diptera: Chaoboridae) towards larval stages of the Culex pipiens (Diptera: Culicidae) mosquito complex. Moreover, we examine the influence of search area variation on selectivity traits, given its importance in consumer-resource interactions. Chaoborids were able to capture and consume mosquito prey across their larval ontogeny. When prey types were available individually, a destabilizing Type II functional response was exhibited towards late instar mosquito prey, whereas a more stabilizing Type III functional response was displayed towards early instars. Accordingly, search efficiencies were lowest towards early instar prey, whereas, conversely, maximum feeding rates were highest towards this smaller prey type. However, when the prey types were present simultaneously, C. flavicans exhibited a significant positive preference for late instar prey, irrespective of water volume. Our results identify larval chaoborids as efficacious natural enemies of mosquito prey, with which they frequently coexist in aquatic environments. In particular, an ability to prey on mosquitoes across their larval stages, coupled with a preference for late instar prey, could enable high population-level offtake rates and negate compensatory reductions in intraspecific competition through size refuge.

Consumptive and non-consumptive effects of predators vary with the ontogeny of their prey.

Predators exert a strong influence on ecological communities by reducing the abundance of prey (consumptive effects) and shaping their foraging behavior (non-consumptive effects). Although the prevalence of trophic cascades triggered by non-consumptive effects is increasingly recognized in a wide range of ecosystems, how its relative strength changes as prey individuals grow in size along various life stages remains poorly resolved. We investigated how the effects of predators vary with the ontogeny of a key herbivorous sea urchin, which is responsible for transforming diverse macroalgal forests to a barren state dominated by bare rock and encrusting coralline algae. We conducted a series of field and laboratory experiments to determine how susceptibility to predation, prey behavioral responses, and grazing impact on algal cover vary with sea urchin size. The consumptive effects of predators were greater on smaller sea urchin size classes, which were more susceptible to predation. Unexpectedly however, predator non-consumptive effects acted only on larger sea urchins, significantly reducing their grazing activity in the presence of predator cues. Crucially, only these larger sea urchins were capable of overgrazing macroalgae in the field, with non-consumptive effects reducing sea urchin foraging activity and macroalgal grazing impact by 60%. The decoupling between risk and fear as prey grow indicates that the strength of consumptive and non-consumptive trophic cascades may act differently at different ontogenetic stages of prey. While the consumptive effects of predators directly influence population numbers, the consequences of non-consumptive effects may far outlive consumptive effects as prey grow, finding refuge in size, but not from fear.

Vulnerability of juvenile clams to predation by shore crabs

Predation, especially by crabs, is a common source of mortality for natural and farmed populations of intertidal clams. Consumption of juvenile “seed clams” forces aquaculturists to try to exclude predators and/or raise juveniles in hatcheries until they can reach a size refuge. We ran a variety of lab experiments assessing vulnerabilities of juvenile clams to small, common shore crabs (Hemigrapsus spp.). Crabs <1 cm width can consume hardshell Manila clams larger than those normally used for “seed”, and can readily crush even larger softshell Mya clams. We suggest that using netting to prevent consumption by shore crabs is not practical given that smaller individuals can fit through mesh openings. Raising seed in hatcheries until they are 10–15 mm will provide a size refuge from shore crabs, but not larger cancrid crabs. Farming on beaches with little habitat (e.g., cobbles) for shore crabs can likely reduce juvenile clam mortality. A better understanding of predation threats to commercially important clams is critical, especially as the invasion of the green crab Carcinus to Washington shorelines further threatens survival of juvenile clams.

Intraspecific predator inhibition, not a prey size refuge, enables oyster population persistence during predator outbreaks

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 602:155-167 (2018) - DOI: https://doi.org/10.3354/meps12704 Intraspecific predator inhibition, not a prey size refuge, enables oyster population persistence during predator outbreaks H. S. Booth1,*, T. J. Pusack2, J. W. White3,4, C. D. Stallings2, D. L. Kimbro1 1Department of Marine and Environmental Sciences, Northeastern University, Marine Science Center, Nahant, MA 01908, USA 2College of Marine Science, University of South Florida, St. Petersburg, FL 33701-5001, USA 3Department of Biology and Marine Biology, University of North Carolina Wilmington, Wilmington, NC 28403, USA 4Department of Fisheries and Wildlife, Coastal Oregon Marine Experiment Station, Oregon State University, Newport, OR 97365, USA *Corresponding author: booth.ha@husky.neu.edu ABSTRACT: Predators commonly structure natural communities, but predation effects can vary greatly. For example, increasing predator densities may not reduce prey populations as expected if intraspecific predator interactions suppress foraging efficiency or if prey size refuges exist. In northeastern Florida (USA), outbreaks of the predatory crown conch Melongena corona have contributed to declines in oyster populations and the commercial oyster fishery. However, despite expectations of oyster population collapse, reefs have persisted, albeit with reduced adult oyster size and living reef biomass. To investigate the mechanism(s) underlying this unexpected persistence, we used field observations and experiments to examine the effects of predator density and prey size on predation rates. Multi-year surveys indicated that large oysters did not experience a predation size refuge, and further suggested that predation rates declined with increased predator density. Consistent with field surveys, field experiments demonstrated that conchs selectively consumed larger oysters (potentially explaining the absence of large oysters on natural reefs) and that high conch densities suppressed per capita predation rates, likely due to intraspecific antagonistic interactions. A Type III ratio-dependent model best described the experimental conch functional response, explaining >50% of the variation in per capita prey consumption and including a signal of reduced attack rates at high predator densities. Thus, although large aggregations of predators have the potential to deplete prey populations, our study illustrates intraspecific predator interactions that possibly prevent the local extirpation of an important habitat-forming prey species. KEY WORDS: Crassostrea virginica · Functional response · Gastropod · Interference · Predator outbreak Full text in pdf format Supplementary material PreviousNextCite this article as: Booth HS, Pusack TJ, White JW, Stallings CD, Kimbro DL (2018) Intraspecific predator inhibition, not a prey size refuge, enables oyster population persistence during predator outbreaks. Mar Ecol Prog Ser 602:155-167. https://doi.org/10.3354/meps12704 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 602. Online publication date: August 23, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

Population collapse dynamics in Acropora downingi, an Arabian/Persian Gulf ecosystem-engineering coral, linked to rising temperature.

As in the tropical Atlantic, Acropora populations in the southern Persian/Arabian Gulf plummeted within two decades after having been ecosystem engineers on most wave-exposed reefs since the Pleistocene. Since 1996/1998 live coral cover in the Gulf declined by over 90% in many areas, primarily due to bleaching and diseases caused by rising temperatures. In the formerly dominant table-coral species A.downingi, population dynamics corresponding to disturbance regimes was quantified in three transition matrices (lower disturbance pre-1996; moderate disturbance from 1998 to 2010 and 2013 to 2017, disturbed in 1996/1998, 2010/11/12, 2017). Increased disturbance frequency and severity caused progressive reduction in coral size, cover, and population fecundity. Small size-classes were bolstered more by partial colony mortality than sexual recruitment. Some large corals had a size refuge and resisted die-back but were also lost with increasing disturbance. Matrix and biophysical larval flow models suggested one metapopulation. Southern, Arabian, populations could be connected to northern, Iranian, populations but this connectivity was lost under assumptions of pelagic larval duration at rising temperatures shortened to a third. Then, the metapopulation disintegrated into isolated populations. Connectivity required to avoid extinctions increased exponentially with disturbance frequency and correlation of disturbances across the metapopulation. Populations became unsustainable at eight disturbances in 15years, when even highest theoretical recruitment no longer compensated mortality. This lethal disturbance frequency was 3-fold that of the moderately disturbed monitoring period and 4-fold of the preceding low-disturbance period-suggesting ongoing shortening of the disturbance-free period. Observed population collapse and environmental changes in the Gulf suggest that A.downingi is heading toward at least functional extinction mainly due to increasingly frequent temperature-induced mortality events, clearly linked to climate change.

Cannibalism as a selective force on offspring size in fish

Cannibalism may cause considerable mortality on juvenile fish and it has been hypothesised that it may exercise selection on offspring size in that larger offspring may enjoy a size refuge. For this to be evolutionarily advantageous the survival of individual offspring must compensate for the reduced fecundity implied by larger offspring size. We develop a model which combines standard assumptions of size‐dependent mortality with adult cannibalism to investigate the potential for cannibalism to act as selective force on offspring size. We find that for this potential to be realised, the mortality due to cannibalism must exceed a threshold value that is a decreasing function of non‐cannibalistic predation intensity, cannibalized size range width and the average cannibalized size. If cannibalism exceeds this threshold, the model predicts evolution of offspring size towards refuges above or below cannibalized size range depending on initial offspring size. Cannibalistic mortality cannot be so great that the population is non‐viable, however, the range of parameter values describing cannibalistic intensity allowed within these boundaries is wide. On this basis, we suggest that cannibalism is a potential mechanism for offspring size selection.

Assemblage-level effects of the introduced peacock hind (Cephalopholis argus) on Hawaiian reef fishes

The peacock hind Cephalopholis argus (family Serranidae), locally known as ‘roi’, was introduced from French Polynesia to Hawaii in the mid-twentieth century as a food fish. However, because of its association with ciguatera fish poisoning, it is rarely fished for food. Previous research indicates that roi could have a negative impact on native reef fish assemblages because of their high densities and prey consumption rates. However, it is unclear whether roi add to the cumulative mortality of prey (predation hypothesis), or whether predation is instead compensatory (doomed surplus hypothesis). This study experimentally assessed the effects of roi on reef fish populations through a long-term (5.5 year) predator removal experiment. A Before-After-Control-Impact study design was used to assess changes in fish assemblages following the removal of roi on 1.3 ha of patch reef. Increases in the density of prey-sized fish (<15 cm TL) were observed 18 months after roi removal. However, those effects did not translate into sustained increases in prey. While increases in potential competitors, wrasses (family Labridae), particularly the piscivorous ringtail wrasse Oxycheilinus unifasciatus, were observed on roi-free reefs, the fish assemblage did not diverge substantially in composition. Native reef fish appeared to resist the potential negative impacts of predation by roi, possibly through a refuge in size for some fish families. Management to protect intact fish assemblage size-structure could serve to bolster native resistance to invading species. In considering the threats facing coral reefs, and the possible solutions, roi removal alone will not likely replenish native fishery resources.

Post-harvest recovery dynamics depend on predator specialization in size-selective fisheries

Author(s): Aalto, EA; Baskett, ML | Abstract: Fisheries typically truncate target species' size distributions through an increase in mortality, especially if harvest is size-selective. Such truncation can push a harvested species' size distribution into classes most vulnerable to gape-limited predation, such that predator-prey dynamics might affect the rate of recovery from fishing. Understanding this rate of recovery is crucial to adaptive management of no-take reserves and fisheries closures. We used a 2-species size-structured model to examine how gape-limited predation alters post-harvest recovery for 3 example prey species, viz. cod, haddock, and whiting. We found little difference in recovery patterns of prey abundance and size structure between systems with gape-limited generalist predation and those with no size-dependent predation. However, gape-limited obligate predation can lead to fluctuations, with transient declines, that delay recovery to the pre-harvest equilibrium for both biomass and mean size due to a time lag in predator recovery. Fluctuating recovery dynamics under obligate predation were most likely for predators that experienced greater declines due to prey loss during harvest and for slow-growing prey with an adult size refuge. We conclude that through these delays, the presence of a strong dynamically linked predator can alter the expec - tations of the time scale for different recovery metrics used in adaptive management.

Effects of size refuge specificity on a predator–prey model

Predation is a major cause of early-stage mortality for prey individuals, which are often forced to use refuges in order to reduce the risk of being consumed. The ability of certain genotypes in a prey population to reach a size refuge from predation may contribute significantly to the preservation of community diversity. We investigate how the specificity of this behavior affects the evolution of a given population by using a modified Lotka-Volterra model, in which the proportion of each genotype available for predation consists of two components: an intrinsic part and a combination from all genotypes present in the population. The trade-off of these components is characterized by a specificity parameter. From the viewpoint of population dynamics, we observe that the ability of the mutant to invade the resident population strongly depends on the values of this parameter. Finally, we describe the possible evolutionary outcomes, analytically and numerically.

Random movement of predators can eliminate trophic cascades in marine protected areas

AbstractThe protection of predators inside marine reserves is expected to generate trophic cascades with predator density increasing but prey density decreasing; however, predators and prey often both increase inside reserves. This mismatch between the expected and observed change in prey density has been explained because prey also are harvested; that is, the protection of prey compensates for the additional predation inside the reserve. Here, we show that this mechanism alone cannot increase densities of predator and prey; other mechanisms are required, and we hypothesized that movement of predator and/or prey might provide such a mechanism. We therefore built two spatially implicit two‐patch predator–prey models with movement of predator and prey between reserve and fishing grounds. We show that post‐settlement movement of predators (but not prey) altered the strength of trophic cascades and could increase densities of both predator and focal prey. We further built a more general model that shows that predator post‐settlement movement can reinforce and even supplement the effect of two previously investigated mechanisms producing trophic cascades: a prey size refuge and predator density‐dependent mortality. Our study increases understanding of mechanisms that can alter the strength (and direction) of prey responses inside marine reserves and highlights the importance of movement in human‐induced heterogeneous systems.

Ontogenetic changes in predator–prey interactions between two species of larval fishes and oyster veligers

The naked goby (Gobiosoma bosc), striped blenny (Chasmodes bosquianus), and eastern oyster (Crassostrea virginica) are common resident species in temperate Atlantic tidal waters. All three species produce planktonic larvae, and interactions between their early life stages likely influence recruitment success. Fish predation on oyster veligers requires co-occurrence as well as a match between prey behavior, size, and morphology and the ability of the predator to capture and engulf the veliger (prey). Wild plankton, oyster veligers, and wild plankton enriched with oyster veligers (mixed) were fed to cultured larval fishes during laboratory experiments. Three hypotheses were tested: (1) no fish species-specific differences in oyster veliger consumption exist within similar predator–prey development stage combinations, (2) postflexion blennies and gobies consume more veligers than preflexion fishes, (3) veligers reach a size refuge from fish predation by the umbo developmental stage. The resulting data provide a quantitative description of larval fish feeding behavior with respect to fish (preflexion, postflexion) and veliger (straight hinge, umbo) developmental stage. Selectivity for bivalve veligers as well as ontogenetic effects on the predator–prey interaction were examined. Fish nests were cultured to provide larval fish predators of known age. Overall, 70% of striped blennies and 59% of naked gobies consumed at least one prey item during the 3h experiments. There were fish species-specific differences in oyster veliger consumption between striped blennies and naked gobies. Striped blennies consumed more prey items including a wider range of veliger ages than larval naked gobies of the same developmental stages, regardless of the prey treatment. Fish selectivity was high for copepod nauplii and bivalve veligers and usually low for polychaete larvae, barnacle nauplii, and diatoms. There was a significant positive relationship between standardized consumption and predator development stage in the wild treatment for both fishes and in mixed and veliger treatments for blennies. All fishes consumed straight hinge veligers more often than umbo stage veligers. The largest veligers appear to reach a predation refuge from both fishes. Larval gobies and blennies are generalist predators that use seasonal pulses of zooplankton prey within temperate estuaries. Potential mismatches between predator–prey spatial and temporal overlap that might reduce fish recruitment are likely offset by adult spawning strategies that result in multiple nests within a long spawning season.

Nonadditive impacts of temperature and basal resource availability on predator-prey interactions and phenotypes.

Predicting the impacts of climate change on communities requires understanding how temperature affects predator-prey interactions under different biotic conditions. In cases of size-specific predation, environmental influences on the growth rate of one or both species can determine predation rates. For example, warming increases top-down control of food webs, although this depends on resource availability for prey, as increased resources may allow prey to reach a size refuge. Moreover, because the magnitude of inducible defenses depends on predation rates and resource availability for prey, temperature and resource levels also affect phenotypic plasticity. To examine these issues, we manipulated the presence/absence of predatory Hynobius retardatus salamander larvae and herbivorous Rana pirica tadpoles at two temperatures and three basal resource levels. and measured their morphology, behavior, growth and survival. Prior work has shown that both species express antagonistic plasticity against one another in which salamanders enlarge their gape width and tadpoles increase their body width to reach a size-refuge. We found that increased temperatures increased predation rates, although this was counteracted by high basal resource availability, which further decreased salamander growth. Surprisingly, salamanders caused tadpoles to grow larger and express more extreme defensive phenotypes as resource levels decreased under warming, most likely due to their increased risk of predation. Thus, temperature and resources influenced defensive phenotype expression and its impacts on predator and prey growth by affecting their interaction strength. Our results indicate that basal resource levels can modify the impacts of increased temperatures on predator-prey interactions and its consequences for food webs.