Relative Predation Rates Research Articles

Development of a castable, GPS enabled, Miniaturized Predation Event Recorder (mPER) to quantify predation of juvenile fishes

Over the past decade, predation-event recorders (PERs) have become an effective tool to estimate relative predation rates of juvenile Chinook salmon in California’s Central Valley. However, due to their design, PERs have primarily been limited to studying predation over relatively large spatial scales (up to several hundred meters or more). Due to this limitation, we designed a simple yet effective, castable, GPS enabled miniaturized predation-event recorder (mPER) based on an Arduino platform that can be adapted to meet individual applications. We tested our mPER by evaluating predation around a small-scale water diversion in the Sacramento-San Joaquin Delta. We modeled the relationship between predation risk and time to sunset as well as distance to diversion with a Cox proportional hazards model, a time-to-event model that accounts for censored data. The results of this proof-of-concept analysis indicated that for each elapsed minute, predation risk decreased by a factor of 0.97, as sunset was approached and passed. Similarly, each meter increase in distance from the diversion decreased the predation risk by a factor of 0.86. The mean relative predation rate in our study area was 24%. Our mPERs proved to be an inexpensive, effective, and reliable tool to quantify predation, in a repeatable manner, around targeted locations of interest. We have included the design, material list, Arduino programming code, and Cox proportional hazard analysis code for others to easily design, use, and analyze the resulting data from our mPER design (supplementary information available from the Open Science Framework https://osf.io/ysm2p/).

Predation on Plasticine Model Caterpillars: Engaging High School Students Using Field-Based Experiential Learning & the Scientific Process

Engaging students in hands-on inquiry helps them develop skills associated with the scientific process. Development of simple experiments using model caterpillars can provide an experiential demonstration of the scientific process and ecological principles for high school students. Caterpillar models are formed from plasticine, a nontoxic, nondrying modeling clay, and are an excellent tool for quantifying relative predation rates by birds, small mammals, and invertebrates. Lifelike surrogate larvae are glued to vegetation for short periods (one week) and retain identifiable marks (beak, teeth, mandible imprints) following predator attack. This technique is simple, inexpensive, and provides rapid and clear results, rendering it a highly effective method of inquiry for high school students. Students can use these methods to ask a variety of research questions, such as comparison of predation in nearby habitats (park vs. backyard), vegetation (tree vs. shrub), season (spring vs. fall), or coloration (aposematic vs. camouflage). For many students, this may be one of few opportunities at the high school level to investigate science “in the field” and integrate scientific practices, such as the scientific method and inquiry, in an authentic research experience. Participants develop their scientific reasoning skills through creation of research questions and interpretation of results. They learn experimental technique, build field skills, and work collaboratively. This experiment aligns with the Next Generation Science Standards.

Contribution of predation to the biological control of a key herbivorous pest in citrus agroecosystems

Biological control has traditionally simplified the view of trophic relationships between herbivorous pests and their natural enemies in agriculture. The success or failure of this pest management strategy is still mainly attributed to the ability of a few key natural enemies to suppress the pest density. For example, successful regulation of the California red scale (Aonidiella aurantii), a key citrus pest, is generally credited to specific parasitoids of the Aphytis genus. Currently, research is revealing how herbivore regulation in agroecosystems can be alternatively achieved with a greater number of trophic associations within the system. The goals of the present study were as follows: i) to unravel species-specific trophic links between A.aurantii and its natural enemies in citrus agroecosystems, and ii) to assess their contribution to control of A.aurantii. Predation and parasitism of this herbivorous pest were assessed through exclusion experiments. Species-specific trophic links between this herbivorous pest and its natural enemies were studied using gut-content analysis of field-collected predators employing prey-specific DNA molecular markers. Relative predation rates of the species involved in A.aurantii regulation were estimated. Predation was found to be the main biotic component of A.aurantii mortality, causing reductions of more than 75% in recently settled cohorts. Aonidiella aurantii DNA was detected in the digestive system of 11 species of predators. Generalist and stenophagous predators, mainly associated with other citrus pests such as aphids, proved to be the most important biological control agents of this pest. Complex trophic relationships, such as apparent competition between two key citrus pests, were revealed. The present study highlights the role of predation as biotic mortality factor of key pests in perennial agroecosystems, wherein it is a rich complex of indigenous or naturalized generalist predators that are primarily responsible for this mortality. The results herein presented may therefore offer another perspective on the biological control of one of the key world-wide citrus pests, at least in those regions where specific parasitoids are not able to successfully regulate the scale populations.

Are predation rates comparable between natural and artificial open-cup tree nests in boreal forest landscapes?

Nest predation studies often use artificial nests to secure sample sizes and nest distribution patterns that allow empirically testing differences in predation rates between ecological units of interest. These studies rely on the assumption that natural and artificial nests experience similar or consistent relative predation rates across ecological gradients. As this assumption may depend on several factors (for example differences in predator community, nest construction, parental care patterns), it is important to test whether artificial nests provide adequate and comparable estimates of predation rates to natural nests. In this study, we compare predation rates of above-ground natural open-cup nests, artificial nests and natural nests with artificial eggs along a forest gradient from edge to interior (interior, transition zone and edge) and within two nest visibility classes (visible and concealed). Our aim was to determine whether nest structure affects comparability between nest types along these ecological gradients in boreal forests. Our results indicated important contributions of nest type, nest visibility and location along the forest edge-interior gradient, but no variable had strong significant effects on predation rates, except exposure time that showed lower predation rates at longer exposure times. Predation rates in visible and concealed nests remained similar for all nest types, but not along the forest edge-interior gradient. Here, artificial nests showed much lower predation rates than natural nests, whereas natural nests with artificial eggs tended to have higher predation rates than natural nests. We conclude that artificial nests in boreal forests represent an adequate measure of relative nest predation risk in open-cup natural nests along some ecological gradients, but results on predation rates along forest edge-interior gradients obtained from artificial nests should be interpreted with care.

Selectivity underlies the dissociation between seasonal prey availability and prey consumption in a generalist predator.

Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to prey availability to maximize energetic intake especially when overall prey availability is low. By extension, they are also expected to feed in a more frequency-dependent manner during winter compared to the more favourable foraging conditions during spring, summer and fall seasons. For 18months, we observed the foraging patterns of forest-dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR-based gut-content analysis and simultaneously monitored the activity densities of two common prey: springtails (Collembola) and flies (Diptera). Rates of prey detection within spider guts relative to rates of prey collected in traps were estimated using Roualdes' cst model and compared using various linear contrasts to make inferences pertaining to seasonal prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low prey densities, the relative rates of predation compared to available prey differed significantly over time and by prey group. Moreover, these spiders appeared to diversify their diets; the least abundant prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient-focused strategy, may also be optimal for generalist predators during prey-scarce winters.

Barcoding PCR primers detect larval lake sturgeon (Acipenser fulvescens) in diets of piscine predators

Population levels of recruitment are often affected by high rates of mortality during early life stages. Lake sturgeon (Acipenser fulvescens), a regionally threatened species, experiences high rates of mortality during the larval stage, partially due to predation. The objective of this study was to quantify and compare relative rates of larval sturgeon predation by piscine predators in the upper Black River (Cheboygan County, MI, USA). A molecular barcoding assay was developed using lake sturgeon-specific primers that amplify a region of mitochondrial DNA cytochrome oxidase I as an alternative to morphological analysis of gastrointestinal (GI) contents to quantify the presence or absence of larval fish collected from potential fish predators (353 specimens, 17 potential predator species). The assay was verified to be sturgeon-specific and sufficiently sensitive to amplify the low quantities of degraded DNA in GI samples. Lake sturgeon DNA was identified in 26 of 353 predator diet samples (7.34%) in 9 of 17 potential predator fish species present. There was a significant positive correlation between the numbers of predators that had consumed larval lake sturgeon and the number of samples from a predator species analyzed. No relationship between predation level and habitat type (sand or gravel substrate) was observed, though predator community composition varied between habitats. Genetic assays as described here can be used to investigate predator–prey dynamics affecting species of conservation interest during important life stages that may otherwise be under-represented in diet studies that rely solely on morphological analysis.

Disentangling fine- and broad- scale effects of habitat on predator–prey interactions

Predator–prey interactions can be influenced by habitat at different spatial scales. In seagrass systems, blade density can provide refugia for prey at fine scales, which are further embedded within broad-scale features such as variation in biotic (e.g., predator assemblages) and abiotic attributes (e.g., turbidity, salinity). Fine-scale effects of seagrass habitats on predator–prey interactions involving invertebrates have been well studied while less is known about their effects on fish as prey. A field experiment was conducted in Tampa Bay, Florida, USA to examine and separate the effects of habitat across fine and broad scales on the relative predation rates of tethered pinfish (Lagodon rhomboides). Artificial seagrass units (ASUs) were used at three levels of blade density and deployed in different locations within the seascape. Predation rates on pinfish decreased with increasing seagrass blade density. The effects of blade density were consistent across locations, but overall mortality was higher in the lower Bay, where the water was less turbid, higher in salinity, and characterized by a different suite of predators compared to the mid Bay. Using controlled-laboratory experiments, it was found that pinfish reduced their activity levels in more turbid water as well as in response to the presence of a common predator in both clear and more turbid waters. Thus, predation rates were influenced by the combined effects of refugia (fine scale), variation in prey behavior (broad scale), and detection by predators (both scales). This study demonstrates the strong influence habitat can have at different spatial scales in mediating predator–prey interactions of mobile species in estuarine environments.

Evaluating potential artifacts of tethering techniques to estimate predation on sea urchins

Measuring the strength of trophic interactions in marine systems has been central to our understanding of community structuring. Sea urchin tethering has been the method of choice to evaluate rates of predation in marine benthic ecosystems. As standardly practiced, this method involves piercing the urchin test, potentially introducing significant methodological artifacts that may influence survival or detection by predators. Here we assess possible artifacts of tethering comparing invasive (pierced) and non-invasive tethering techniques using the sea urchin Paracentrotus lividus. Specifically, we looked at how degree of confinement and high water temperature (first order artifacts) and predator guild and size of the prey (second order artifacts) affect the survival and/or detectability of pierced urchins. Our results show that first order artifacts only arise when pierced sea urchins are placed in sheltered bays with confined waters, especially when water temperature reaches extremely high levels. Prey detectability did not increase in pierced sea urchins for the most common predators. Also, test piercing did not alter the preferences of predators for given prey sizes. We conclude that the standard tethering technique is a robust method to test relative rates of sea urchin predation. However, local conditions could increase mortality of the tethered urchin in sheltered bays or in very high temperature regimes. Under these conditions, adequate pierced controls (within predator exclusions) need to be included in assays to evaluate artifactual sources of mortality.

Do changes in reef habitats influence relative predation risk on the juvenile Australasian spiny lobster, Jasus edwardsii (Hutton, 1875)?

Kelp habitats are in decline in many temperate coastal regions of the world due to climate change and expansion of populations of grazing urchins. The loss of kelp habitat may influence the vulnerability to predators of the juveniles of commercially important species. In this study relative predation rates for kelp versus barren reef habitat were measured for early juvenile Australasian spiny lobster, Jasus edwardsii (Hutton, 1875), on the northeastern coast of New Zealand using tethering methods. Variation in assemblages of predators over small spatial scales appeared to be more important for determining the relative predation of lobsters, regardless of habitat type. Therefore, the assessment of relative predation risk to early juvenile lobsters between kelp and barren habitats will require more extensive sampling at a small spatial scale, as well as a specific focus on sampling during crepuscular and nocturnal periods when these lobsters are most at risk of predation.

Putative Predators of Carcinus Maenas in Eastern Australia

Following the arrival of non-native species into suitable environments, interactions with native biota can influence non-native species proliferation and spread. The European shore crab, Carcinus maenas, is a global invader for which top-down control by predators has been implicated in limiting range expansion in its North American range. Little is known, however, about predators of this non-native species within its Australian distribution. We conducted quarterly trapping over 2 years in ten Australian estuaries to assess relationships between the abundance of C. maenas and native predators. Feeding assays between C. maenas and putative predators, identified from negative associations in occurrence, assessed the ability of putative predators to recognise C. maenas as prey. Six taxa were negatively correlated with C. maenas’ abundance and capable of eating the non-native crab. These were the blue swimmer crab (Portunus pelagicus), octopods (Octopus spp.), leatherjackets (Monocanthidae), yellowfin bream (Acanthopagrus australis), toadfish (Tetraodontidae) and the eastern fiddler ray (Trygonorrhina fasciata). Octopus spp. were rare in and blue swimmer crabs absent from mangroves; the habitat in which C. maenas was most abundant. A tethering experiment confirmed that Octopus spp. eat C. maenas in the field, with greater rates of mortality of the crab close to than away from the Octopus spp. lairs. Overall, our study indicates that a diverse assemblage of predators may prey upon C. maenas in southeastern Australia. Further studies assessing relative rates of predation by these predators on C. maenas are needed to assess whether they are exerting significant top-down control.

Determining predator identity from attack marks left in model caterpillars: guidelines for best practice

AbstractThe use of model caterpillars to assess relative rates of predation has risen in popularity in recent years. Among the various benefits of the technique is its capacity to provide information on the identity of attackers through the impressions left in the modelling clay from which the model prey is constructed. However, there currently exists no detailed information on how to assign attack marks to particular predators. We aimed to address this gap by collating a comprehensive reference collection of the types of marks made by different predators to serve as a guide for researchers wanting to identify the predators responsible for attacks. To determine what level of resolution in identification may be considered reliable, we also tested the consistency of predator assignments made by different individuals. We found that predator identification at a coarse taxonomic level (i.e., bird, mammal, arthropod) was reasonably consistent. In contrast, when more fine‐scale identification was attempted, the level of consistency and therefore also confidence in the accuracy of an identification was dramatically reduced, reflecting the difficulty of distinguishing between attacks made not only by different arthropod groups but also by differently sized birds and mammals. We recommend that identifications be made at a coarse taxonomic level and, where possible, by multiple individuals. We also suggest that our collection of images of representative attack marks from each of the coarse predator categories, and descriptions of their defining characteristics, can serve as a guide to assist with identifications and this will be complemented by a good knowledge of the locally occurring and abundant predators.

Nest predators of southeast Asian evergreen forest birds identified through continuous video recording

Using continuous video recording, we identified predation as the main cause of nest failure of understorey‐nesting birds in an intact evergreen forest in northeastern Thailand. Our dataset of 87 predation events is the largest recorded in the tropics. The main predators were macaques (n = 38; 43.7%), nocturnal snakes (n = 19; 21.8%), non‐raptorial birds (n = 12; 13.8%), raptors (n = 6; 6.9%), squirrels (n = 5; 5.7%) and tree shrews (n = 4; 4.6%). The two most important predators, Pig‐tailed Macaque Macaca nemistrina and Green Cat Snake Boiga cinerea, showed no preference for nest type, nest stage or nest height and we found no difference in their relative predation rates among years. Predation was predominantly diurnal (73.6%), suggesting that visual cues may be important for predators at this site.

Effects of predation and habitat structure on the abundance and population structure of the rock shrimp Rhynchocinetes typus (Caridea) on temperate rocky reefs

Human disturbances, such as overfishing, may disrupt predator–prey interactions and modify food webs. Underwater surveys were carried out at six shallow-water reef barrens in temperate waters of northern-central Chile from October to December 2010 to describe the effects of predation, habitat complexity (low, medium and high) and refuge availability on the abundance and population structure of the rock shrimp Rhynchocinetes typus (Rhynchocinetidae), an important mesoconsumer on subtidal hard substrata. Three sites were within managed (restricted access) areas for fishermen, and three were unmanaged (open-access). Field observations and tethering experiments were conducted to examine the relationship between fish and shrimp abundances, and the relative predation rates on shrimps. Direct effects of predation on R. typus body-size distribution were examined from shrimps collected in the field and fish stomachs. The presence and the abundance of R. typus increased with habitat reef complexity and refuge availability. Shrimp abundance was negatively related to fish abundance in managed areas, but not in open-access areas, where shrimp densities were the highest. Also, predation rates and body-size distribution of shrimps were unrelated, although fish consumed more large shrimps than should be expected from their distribution in the field. R. typus occurred most often in shelters with wide openings, offering limited protection against predators, but providing potential aggregation sites for shrimps. Overall, direct effects of predation on shrimp densities and population structure were weak, but indirect effects on shrimp distribution within reefs appear to have been mediated through behavioural responses. Our study highlights the need to assess both numerical and behavioural responses of prey to determine the effects of predator loss on mesoconsumer populations.Electronic supplementary materialThe online version of this article (doi:10.1007/s00227-012-1994-6) contains supplementary material, which is available to authorized users.

Nest-predator prevalence along a mountain birch - alpine tundra ecotone

Context Nest predation is a major factor influencing life history and population dynamics of ground-nesting birds. The transitions between the northern boreal mountain birch forests and the low-alpine tundra are important habitats for the willow ptarmigan, Lagopus lagopus (Linnaeus, 1758). During the past decades, these landscapes have been extensively developed with cabin resorts in southern Norway, which has led to an increased number of roads and foot paths in relatively undisturbed habitats. Aims The aim of the present study was to investigate relative nest-predation rates in elevation gradients (ecotones) spanning from northern boreal mountain birch forests to low-alpine tundra in three locations with contrasting willow ptarmigan densities. Methods We conducted an artificial nest study by using baited track boards (n = 108). Track boards were placed along transects (200 m) in the following three habitat types: birch forest, edge habitat and low-alpine tundra. Predator prevalence was analysed in relation to study-design variables (location, habitat, study period) and the load of human infrastructure (i.e. distance to foot paths and roads), using generalised linear mixed-effect models assuming binomial distribution for the response variable. Key results Prevalence of avian predators was consistently high (range 38.2–85.3%), in contrast to much lower prevalence of mammalian predators (range 2.8–22.9%). Raven (Corvus corax) was the dominant nest predator, followed by hooded crow (C. cornix) and pine marten (Martes martes). Location, as contrasted by differences in willow ptarmigan density, was not significantly related to total relative predation rates. Species-specific predator prevalence was habitat specific and related to human infrastructure, but with opposite relative predation patterns between pine marten and raven. Hooded crow predation was similar across the ecotone and not related to human infrastructure. Conclusions Predator prevalence was habitat specific and affected by human infrastructure (distance to human foot paths). Our study confirmed that human activity might alter the predation rates by generalist species in these low-alpine environments. Implications We recommend that attractive willow ptarmigan habitat should be avoided when planning human infrastructure in alpine ecosystems. To reduce predation pressure in this ecosystem, it appears that generalist predators should be considered for management actions. Further research is needed to explain the underlying mechanism driving expansion of generalist species into alpine habitats. Such knowledge is also important in developing alternative management actions with focus other than predator control.

Prevalence of nest predators in a sub-Arctic ecosystem

High nest loss is an important driver of gallinaceous bird population dynamics. Identifying factors determining the spatial distribution of potential nest predators and thereby indirectly risk of nest losses is therefore essential. The aim of this 1-year study was to estimate relative predation rates on artificial ground nests in willow ptarmigan (Lagopus lagopus) habitats, along replicate altitudinal gradients (transects, n = 60) spanning from sub-Arctic birch forest to the low-alpine tundra in three locations in northern Norway. In each transect, one artificial nest (track board) was placed in three different habitats: (1) birch forest, (2) edge between birch forest and low-alpine tundra and (3) low-alpine tundra. Total predation rates over all habitats within locations ranged from 47.4% to 77.5% and did not vary systematically in space and time. The average predation rate by avian predators was consistently high (58%), and mammalian predation rate was consistently low (5.6%). The consistently high level of predation inflicted by birds was mainly due to omnipresent corvids, especially the hooded crow (Corvus cornix). Analysis of species-specific predation rates showed that habitat and location effects were insignificant for all species, except for raven (Corvus corax) that showed clearly higher predation in one of the locations. The results indicate that from the perspective of the spatial distribution of potential nest predators in sub-Arctic birch forest, ground nesting birds like willow ptarmigan should not be expected to be selective with respect to nesting habitat in the ecotone between birch forest and the low-alpine tundra.

Honey, I cooled the cods: Modelling the effect of temperature on the structure of Boreal/Arctic fish ecosystems

Historically colder regions of the North Atlantic had fisheries dominated by only a few fish species; principally cod and capelin. Possible population dynamic mechanisms that lead to such dominance are investigated by considering how a charmingly simple published multispecies model of the North Sea would react if the system operated at a lower temperature. The existing model equations were modified to describe temperature effects on growth, fecundity and recruitment and the model was rerun based on typical temperatures for the North Sea and a colder system. The results suggest that total fish biomass in the colder system increases but the community is more vulnerable to a given rate of fishing mortality. In the colder system, within species density dependence is reduced but relative predation rates are higher. Consequently, intermediate-sized species are vulnerable to relatively high levels of predation throughout their life history and tend to be excluded, leading to a system dominated by small and large species. The model helps to explain how temperature may govern coexistence and competitive exclusion in fish communities and accounts for the observed dominance of small and large species in Boreal/Arctic ecosystems.

Testing the differential predation hypothesis for the invasion of rusty crayfish in a stream community: laboratory and field experiments

Summary1. We tested the hypothesis that the non‐native rusty crayfish (Orconectes rusticus) is less vulnerable to predators than two native species (O. propinquus and O. obscurus) it is replacing in streams of the upper Susquehanna River catchment (New York, U.S.A.).2. We used laboratory experiments to compare species‐specific predation rates by smallmouth bass (Micropterus dolomieu) on crayfish of equal size and field tethering experiments to compare relative predation rates between native O. propinquus and non‐native O. rusticus by the suite of crayfish predators in our system. We predicted that crayfish size would affect predation rate but that predation rates would be equal among species when size was controlled.3. We also tested for two potential artefacts of tethering. We tethered crayfish in cages to test whether the ability to escape from tethers is size specific, and we tested whether tethering alters differential predation among crayfish species by the smallmouth bass.4. In the laboratory, smallmouth bass predation on rusty crayfish was lower than on either of the native species. In the field, predation risk for tethered crayfish was inversely related to size but did not differ among species when size was taken into account. Because rusty crayfish in the field experiment were slightly larger than the native species, as in nature, mortality was overall lower for the rusty crayfish.5. In cages, smaller crayfish were more probably to escape from tethers than larger ones, an artefact that may partially confound results from our tethering experiments. Unexpectedly, tethering nearly eliminated predation by smallmouth bass. This artefact prevented us from testing for an interaction of tethering with differential predation and means that the results of field tethering experiments do not include any contribution from smallmouth bass predation.6. Our experiments highlight the importance of explicitly considering potential artefacts that could confound results.7. Our results indicate that differential predation contributes to the rusty crayfish's invasion of a stream community. In our study system, predation rates on rusty crayfish are lower than for native species mostly because of selection by predators for smaller crayfish; species‐specific characteristics such as behaviour that further reduce predation may also contribute, especially where smallmouth bass predation is important.

Interactive effects of episodic hypoxia and cannibalism on juvenile blue crab mortality

We hypothesized that as the spatial extent of hypoxic bottom water increased, (1) adult blue crab predator densities would increase in shallow habitats as they avoided hypoxia, and that (2) juvenile blue crabs, which use shallow unvegetated habitat as a predation refuge from adult conspecifics, would experience increased mortality rates during crowding by cannibalistic adult blue crabs. These hypotheses were tested along a depth gradient of sandy-mud shoreline in the Neuse River Estuary (NRE), North Carolina, USA using a combination of (1) hydrographic measurements to characterize the spatial extent of hypoxia, (2) beach seines to quantify the density of adult blue crab predators in relatively shallow water as a function of 1, and (3) tethering experiments to quantify relative rates of predation on juvenile blue crabs as a function of 1 and 2. During our seven tethering experiments, the NRE study site experienced a range of DO scenarios including normoxia, chronic hypoxia, and hypoxic upwelling. No known predators of juvenile blue crabs, other than adult conspecifics, were collected in any of our shallow-water seines. During the transition from normoxia to chronic hypoxia, blue crab predator densities in shallow refuge habitats increased 4-fold, and relative mortality rates of juvenile blue crabs in shallow habitats increased exponentially with the density of adult conspecifics. Conversely, during hypoxic upwelling events, the density of adult blue crabs in shallow water declined, which may explain why the relative mortality of juvenile crabs did not increase significantly with the increasing spatial extent of hypoxia. Thus, juvenile blue crabs may be relatively safe from adult conspecifics during hypoxic upwelling events, but not during chronic hypoxia. These experimental results highlight the need to consider the effects of dynamic water quality on mobile consumers emigrating from degraded habitats when considering indirect trophic impacts beyond the immediate area of impact.

Experimental Substrate Affects Rate of Seed Removal in Assays of Invertebrate Seed Predation

Postdispersal seed predation by ground beetles may be an important form of biological weed control. Field experiments conducted in 2002 and 2003 determined invertebrate seed predators' ability to detect and remove seeds from different experimental substrates. Predation of wild mustard and common lambsquarters was greater when seeds were presented on sand compared with the two types of synthetic finishing pads; however, predation of velvetleaf, redroot pigweed, and hairy galinsoga was unaffected by substrate. Predation rates were not consistent across all experimental substrates. Estimates of invertebrate predation of common lambsquarters, yellow foxtail, and velvetleaf were greater for seeds offered on sand or synthetic pads than for seeds offered on soil or double-sided tape covered with soil. Although each substrate would be useful to estimate treatment effects on relative predation rates, the weed species by substrate interaction should be considered when comparing predation rates across experiments or when the absolute rate predation is of critical importance.

Stock enhancement of rock lobsters (Jasus edwardsii): timing of predation on naïve juvenile lobsters immediately after release

The success of enhancement programmes hinges on the survival of released animals. One factor greatly influencing short‐term survival of reseeded lobsters is the timing and intensity of predation relative to the time of release. The activity and abundance of predators varies over daily, seasonal, and annual scales and knowing the best time to release juveniles will minimise mortality. We used chronographic tethering devices and remote video equipment at 10 sites near Wellington, New Zealand and Hobart, Tasmania, Australia, to assess the relative timing and intensity of predation for released lobsters. Our studies showed that predation was greatest within the first 2 h after release (χ 2 = 60.425, d.f. = 9, P < 0.001) suggesting that the disturbance associated with the release itself may draw the unwanted attention of predators. Relative predation rates also peaked on each of the following two mornings, possibly because of the emergence of daytime predators. The video footage obtained at the Tasmanian sites revealed that most predation was by fish (46%), but surprisingly, cannibalism comprised 16% of predation events. The limitations of tethering as a method are discussed in numerous reviews but proved useful as a relative measure for these highly mobile and cryptic animals. Further consideration needs to be given to methods of release that minimise mortality of recently seeded lobsters.