Increasing abundance and diversity in the moth assemblage of east Loch Lomondside,Scotland over a 35 year period

Macro-moths caught in a Rothamsted trap, operating from 1968 to 2003 as part of the Rothamsted Insect Survey, were used to investigate the long-term population trends of moth populations on East Loch Lomondside. In total 367 species of macro moth were recorded during this study. Over the 35 years of this study, an increase was recorded in both the overall number of individuals and moth diversity. Mean annual temperature significantly predicted the change in moth diversity but not number of individuals caught. Four of the most consistently abundant species, collectively constituting 27% of the average annual catch, were subjected to more detailed analysis. The three species that emerge during the summer months Eulithis populata (the northern spinach), Hydriomena furcata (july highflier) and Idaea biselata (the small fan-footed wave) became more abundant throughout the study period, (although for the latter species not significantly so). For Eulithis populata and Idaea biselata their emergence time became earlier, over the study period and in Eulithis populata and Hydriomena furcata, the flight duration also became longer. In contrast, the species that emerges as an adult during autumn and winter, Epirrita dilutata (the november moth) did not exhibit a significant change in abundance, emergence date or flight duration in this study. The results suggest that climate change is at least in part, responsible for the observed changes in species dynamics.     

Experimental assessment of predation risk for juvenile green sturgeon,Acipenser medirostris,by two predatory fishes

Predation is a common cause of early life stage mortality in fishes, with reduced risk as individuals grow and become too large to be consumed by gape-limited predatory fishes. Large-bodied species, such as sturgeon, may reach this size-refuge within the first year. However, there is limited understanding of what this size threshold is despite the value of this information for conservation management. We conducted laboratory-based predation experiments on juvenile green sturgeon, Acipenser medirostris, to estimate vulnerability to predation during outmigration from their natal reaches in California to the Pacific Ocean. Two highly abundant and non-native predatory fish species (largemouth bass, Micropterus salmoides, and striped bass, Morone saxatilis) were captured in the wild to be tested with developing juvenile green sturgeon from the UC Davis Green Sturgeon Broodstock Program. Experimental tanks, each containing five predators, received thirty prey for 24-hr exposures. Between sturgeon prey trials, predators were exposed to alternative prey species to confirm predators were exhibiting normal feeding behaviors. In addition to green sturgeon mortality data, trials were video recorded and predatory behaviors were quantified. Overall, these predator species displayed much lower rates of predation on juvenile green sturgeon than alternate prey. Predation decreased with green sturgeon size, and predation risk diminished to zero once sturgeon reached a length threshold of roughly 20–22 cm total length, or between 38% and 58% of predator total length. Behavioral analyses showed low motivation to feed on green sturgeon, with both predators attempting predation less frequently as sturgeon grew. Results of this study imply that optimizing growth rates for larval and juvenile sturgeon would shorten the time in which they are vulnerable to predation. Future experiments should assess predation risk of juvenile green sturgeon by additional predator species common to the Sacramento-San Joaquin watershed.     

The effect of different ant species on the olive moth, Prays oleae (Bern.), in Spanish olive orchard

Abstract:  In the olive orchards of Granada, Spain, ants are one of the most abundant insect families. Two sites were compared in 1994 and 1995 – a commercial orchard and an abandoned one. In both, the temporal pattern of abundance and the ant species composition were similar. Drought affected captures between the years. The managed orchard had fewer species and was dominated by Tapinoma nigerrimum. Predation studies using enzyme-linked immunosorbent assay (ELISA) showed that the maximum number of ants found to be test positive for olive moth, Prays oleae remains coincided with the moth's most vulnerable period. In the commercial orchard the most abundant ant species also had, by far, the highest number of positives for predation whereas at the abandoned site several species were of equal importance. Trophallaxis and scavenging are two particular traits of ants that may artificially inflate the ELISA results. However, as a basis for further study, ELISA can greatly assist the identification of ant species which warrant further research into their possible role against the olive moth.     

Predator Generalization Decreases the Effect of Introduced Predators in the San Marcos Salamander,Eurycea nana

The introduction of novel predators into an environment can have detrimental consequences on prey species, especially if these species lack the ability to recognize these predators. One such species that may be negatively affected by introduced predators is the federally threatened San Marcos salamander (Eurycea nana). Previous research found that predator‐naïve (captive‐hatched) salamanders showed decreased activity in response to the chemical cues of both a native fish predator (Micropterus salmoides) and an introduced fish predator (Lepomis auritus), but not to a non‐predatory fish (Gambusia geiseri). We tested the hypothesis that E. nana recognized the introduced Lepomis (and other non‐native Lepomis) because they share chemical cues with other native congeneric Lepomis predators in the San Marcos River. We examined the antipredator response of predator‐naïve E. nana to chemical cues from (1) a sympatric native sunfish (Lepomis cyanellus; Perciformes: Centrarchidae); (2) a sympatric introduced sunfish (L. auritus); (3) an allopatric sunfish (Lepomis gibbosus); (4) a sympatric non‐native, non‐centrarchid cichlid (Herichthys cyanoguttatum; Perciformes: Cichlidae); and (5) a blank water control to determine whether individuals make generalizations about novel predators within a genus and across a family. Exposure to chemical cues from all fish predator treatments caused a reduction in salamander activity (antipredator response). Additionally, there were no differences in the antipredator responses to each predatory fish treatment. The similar responses to all sunfish treatments indicate that E. nana shows predator generalization in response to novel predators that are similar to recognized predators. Additionally, the antipredator response to H. cyanoguttatum indicates that predator generalization can occur among perciform families.     

Death feigning as an adaptive anti‐predator behaviour: Further evidence for its evolution from artificial selection and natural populations

Death feigning is considered to be an adaptive antipredator behaviour. Previous studies on Tribolium castaneum have shown that prey which death feign have a fitness advantage over those that do not when using a jumping spider as the predator. Whether these effects are repeatable across species or whether they can be seen in nature is, however, unknown. Therefore, the present study involved two experiments: (a) divergent artificial selection for the duration of death feigning using a related species T. freemani as prey and a predatory bug as predator, demonstrating that previous results are repeatable across both prey and predator species, and (b) comparison of the death‐feigning duration of T. castaneum populations collected from field sites with and without predatory bugs. In the first experiment, T. freemani adults from established selection regimes with longer durations of death feigning had higher survival rates and longer latency to being preyed on when they were placed with predatory bugs than the adults from regimes selected for shorter durations of death feigning. As a result, the adaptive significance of death‐feigning behaviour was demonstrated in another prey–predator system. In the second experiment, wild T. castaneum beetles from populations with predators feigned death longer than wild beetles from predator‐free populations. Combining the results from these two experiments with those from previous studies provided strong evidence that predators drive the evolution of longer death feigning.     

Amphipod (Gammarus minus) responses to predators and predator impact on amphipod density

Recent theoretical work suggests that predator impact on local prey density will be the result of interactions between prey emigration responses to predators and predator consumption of prey. Whether prey increase or decrease their movement rates in response to predators will greatly influence the impact that predators have on prey density. In stream systems the type of predator, benthic versus water-column, is expected to influence whether prey increase or decrease their movement rates. Experiments were conducted to examine the response of amphipods (Gammarus minus) to benthic and water-column predators and to examine the interplay between amphipod response to predators and predator consumption of prey in determining prey density. Amphipods did not respond to nor were they consumed by the benthic predator. Thus, this predator had no impact on amphipod density. In contrast, amphipods did respond to two species of water-column predators (the predatory fish bluegills, Lepomis macrochirus, and striped shiners, Luxilus chrysocephalus) by decreasing their activity rates. This response led to similar positive effects on amphipod density at night by both species of predatory fish. However, striped shiners did not consume many amphipods, suggesting their impact on the whole amphipod “population” was zero. In contrast, bluegills consumed a significant number of amphipods, and thus had a negative impact on the amphipod “population”. These results lend support to theoretical work which suggests that prey behavioral responses to predators can mask the true impact that predators have on prey populations when experiments are conducted at small scales. Received: 21 March 1997 / Accepted: 15 December 1997     

Herbivore species richness, composition and community structure mediate predator richness effects and top-down control of herbivore biomass

Changes in predator species richness can have important consequences for ecosystem functioning at multiple trophic levels, but these effects are variable and depend on the ecological context in addition to the properties of predators themselves. Here, we report an experimental study to test how species identity, community attributes, and community structure at the herbivore level moderate the effects of predator richness on ecosystem functioning. Using mesocosms containing predatory insects and aphid prey, we independently manipulated species richness at both predator and herbivore trophic levels. Community structure was also manipulated by changing the distribution of herbivore species across two plant species. Predator species richness and herbivore species richness were found to negatively interact to influence predator biomass accumulation, an effect which is hypothesised to be due to the breakdown of functional complementarity among predators in species-rich herbivore assemblages. The strength of predator suppression of herbivore biomass decreased as herbivore species richness and distribution across host plants increased, and positive predator richness effects on herbivore biomass suppression were only observed in herbivore assemblages of relatively low productivity. In summary, the study shows that the species richness, productivity and host plant distribution of prey communities can all moderate the general influence of predators and the emergence of predator species richness effects on ecosystem functioning.     

Predator Avoidance and Alarm-response Behaviour in Kin-discriminating Tadpoles (Rana cascadae)

When captured by predators, the tadpoles of some species of frogs and toads may release an alarm substance that alters the behaviour of conspecifics. Such ‘alarm response’ behaviour has been proposed as a potential mechanism whereby related conspecifics may ‘warn’ relatives of a predator's presence and thus, improve their inclusive fitness. We examined predator avoidance and alarm response behaviour in tadpoles of the Cascades frog (Rana cascadae) and tested whether such behaviour is influenced by kinship factors. Tadpoles reduced activity when in the presence of a predatory newt (Taricha granulosa). Individuals in sibling groups were more active than both solitary tadpoles and individuals in mixed groups of siblings and nonsiblings. However, we found no evidence of an alarm response in R. cascadae. Behaviour of tadpoles in groups exposed only to predators was not different from that of tadpoles in groups exposed to predators plus crushed conspecifics. Tadpoles in groups exposed to crushed tadpoles were as active as tadpoles in groups exposed to water controls, and some test individuals fed upon the dead tadpoles. Thus, while R. cascadae tadpoles reduce activity in response to newt predators, crushed tadpoles appear to initiate a feeding response rather than an alarm response as has been previously proposed.     

The influence of predator regime on the behaviour and mortality of a freshwater amphipod, <Emphasis Type="Italic">Gammarus pulex</Emphasis>

In species with restricted dispersal, traits may become genetically fixed leading to local adaptations. Therefore, predator avoidance in a prey species may differ between populations experiencing different predator regimes, but also between sexes within a population due to different vulnerability to predators. In this study we used male and female Gammarus pulex from two different predator regimes: fishless ponds, where invertebrates are the dominant predators and ponds with predatory fish. In the laboratory we examined refuge use, mortality, leaf decomposition rate and pair-formation in G. pulex when exposed to predator cues from either invertebrate predators or fish. Individuals from fish ponds spent more time in refuge and had a higher mortality than those from fishless ponds independent of predator cues. There was no effect of pond predator regime or predator cues on leaf decomposition rates. Further, fewer individuals formed pairs in G. pulex from fish ponds than from fishless ponds. Male G. pulex had a higher mortality and a higher decomposition rate than females independent of predator cues. However, there was no difference in refuge use between sexes. Our study shows that there are general differences in behaviour traits, both between predator regimes and sexes in G. pulex.     

Species composition and activity of bats flying over rivers in the Białowieża Primeval Forest

Bats were netted at two sites over the forest rivers Narewka and Hwoźna in Białowieża Primeval Forest (E Poland), during the summer of 1994 and 1995. A total of 452 bats of 11 species were captured. The number of bats netted each night was positively correlated with the minimum air temperature. The rate at which the three commonest species —Nyctalus noctula, Myotis daubentonii andNyctalus leisleri — were caught varied significantly through the night, with a major peak after sunset. ForN. noctula air temperature was apparently positively related to the size of the morning peak.     

Fleeing towards death – leech‐induced behavioural defences increase freshwater snail susceptibility to predatory fish

Prey species are often exposed to multiple predators, which presents several difficulties to prey species. This is especially true when the response to one predator influences the prey’s susceptibility to other predators. Predator‐induced defences have evolved in a wide range of prey species, and experiments involving predators with different hunting strategies allow researchers to evaluate how prey respond to multiple threats. Freshwater snails are known to respond to a variety of predators with both morphological and behavioural defences. Here we studied how freshwater snails Radix balthica responded behaviourally to fish and leech predators, both separately and together. Our aim was to explore whether conflicting predator‐induced responses existed and, if so, what effect they had on snail survival when both predatory fish and leeches were present. We found that although R. balthica increased refuge use when exposed to predatory fish, they decreased refuge use when exposed to predatory leeches. When both predators were present, snails showed a stronger response towards leech than fish and responded by leaving the refuge. This response made the snails more susceptible to fish predation, which increased snail mortality when exposed to both fish and leech compared to fish only. We show that predators that have a relatively low predation rate can substantially increase mortality rates by indirect effects. By forcing snails out of refuges such as rock and macrophyte habitats, leeches can indirectly increase predation from molluscivorous fish and may thus affect snail densities.     

Prey‐processing by avian predators enhances virus transmission in the gypsy moth

The Lymantria dispar nucleopolyhedrovirus (LdNPV) is one of the most important regulators of gypsy moth populations, but some aspects of its transmission remain poorly understood, particularly its high rate of spatial spread and ability to persist in low‐density populations. We tested the role of predatory birds in the transmission of this virus using experimental gypsy moth populations in an aviary. Predatory birds captured virus‐infected caterpillars and facilitated viral dispersal via two processes: 1) by ingesting infected caterpillars and passing viral occlusion bodies (OBs) through their guts, and 2) by scattering OBs during predator‐specific processing behaviors, a mechanism documented here for the first time. The relative importance of both pathways differed by predator species. After eating virus‐infected gypsy moth larvae, red‐eyed vireos and black‐capped chickadees passed more gypsy moth nucleopolyhedrovirus in feces than did gray catbirds. During prey‐processing, the repetitive beating of caterpillars by red‐eyed vireos, a behavior that was rarely utilized by chickadees and catbirds, resulted in the scattering of infectious virus. Due to the combination of efficient gut passage and virus spread from prey beating, higher rates of transmission occurred in experimental gypsy moth populations exposed to red‐eyed vireos than those exposed to catbirds or chickadees. Our results show that effective virus transmission was achieved when virus was vectored by predatory birds through a combination of both behavioral and physiological traits.     

Facilitation and interference among three predators affect their consumption of a stream-dwelling mayfly

1. We experimentally tested if a multiplicative risk model accurately predicted the consumption of a common mayfly at risk of predation from three predator species in New Zealand streams. Deviations between model predictions and experimental observations were interpreted as indicators of ecologically important interactions between predators. 2. The predators included a drift‐feeding fish [brown trout (T), Salmo trutta], a benthivorous fish [galaxiid (G), koaro, Galaxias brevipennis] and a benthic predatory stonefly (S; Stenoperla sp.) with Deleatidium sp. mayflies as prey. Eight treatments with all predator species combinations and a predator‐free control were used. Experiments were performed in aquaria with cobbles as predator refuges for mayflies and we measured the proportion of prey consumed after 6 h for both day and night trials. 3. Trout consumed a higher proportion of prey than other predators. For the two predator treatments we found less than expected prey consumption in the galaxiid + trout treatment (G + T) for both day and night trials, whereas a higher than expected proportion of prey was consumed during night time in the stonefly + trout (S + T) treatment. 4. The results indicate interference (G + T) and facilitation (S + T) between predators depending on predator identity and time of day. Thus, to make accurate predictions of interspecific interactions, it is necessary to consider the ecology of individual species and how differences influence the direction and magnitude of interactions.     

Losing anti‐predatory behaviour: A cost of translocation

Translocation of endangered species to habitats where exotic predators have been removed is now a common conservation practice around the world. Many of these translocated populations have thrived, and they are often used as sources for the harvesting of individuals for translocations to sites where exotic predators still exist, albeit at reduced densities. This study investigates how isolation from exotic predators affects the ability of individuals to recognize such predators using the North Island robin (Petroica longipes) as a model. The study was carried out in three robin populations in the North Island, New Zealand: a translocated population on Tiritiri Matangi Island, where exotic mammalian predators are absent; a population reintroduced from Tiritiri Matangi Island to Wenderholm Regional Park, a mainland site where these mammals are controlled to low densities; and a mainland population at Benneydale where exotic predatory mammals are common. The response intensity of robins to a model stoat was high at Benneydale and low at Tiritiri Matangi and Wenderholm. This result indicates that isolation from mammalian predators on Tiritiri Matangi has suppressed the ability of North Island robins to recognize these predators. It is possible that the low predatory mammal densities at Wenderholm have reduced robin contact with stoats, therefore reduced the opportunity for robins to learn to recognize stoats. Thus, translocation of individuals from populations without predators to places where key predators still exist could be unsuccessful if translocated individuals fail to perform appropriate anti‐predator behaviours.     

Airborne dispersal ofPhytoseiulus persimilis (Acarina:Phtyoseiidae) from a raspberry garden in New Zealand

Airborne dispersal of the predatory mitePhytoseiulus persimilis Athias-Henriot and its preyTetranychus urticae Koch was recorded by trapping mites in silicon grease on microscope slides mounted on a cross-shaped frame placed horizontally 2.5 m above ground level (0.5 m above the top of the crop). Both species were also recorded on raspberry foliage, and population changes there were closely mirrored by numbers caught in the trap.Phytoseiulus persimilis was trapped on slides and recovered from foliage until leaf fall which occurred 6 weeks after the last prey was found. The decline in predator numbers on the foliage closely followed the decline in prey numbers, but the decline of predators on the aerial trap more closely mirrored the decline in the proportion of sample leaves with predators.     

Shift in predation regime mediates diversification of foraging behaviour in a dragonfly genus

1. Behavioural adaptations to avoid and evade predators are common. Many studies have investigated population divergence in response to changes in predation regime within species, but studies exploring interspecific patterns are scant. Studies on interspecific divergence can infer common outcomes from evolutionary processes and highlight the role of environmental constraints in shaping species traits. 2. Species of the dragonfly genus Leucorrhinia underwent well‐studied shifts from habitats being dominated by predatory fish (fish lakes) to habitat being dominated by predatory invertebrates (dragonfly lakes). This change in top predators resulted in a set of adaptive trait modifications in response to the different hunting styles of both predator types: whereas predatory fish actively search and pursue prey, invertebrate predator follow a sit‐and‐wait strategy, not pursuing prey. 3. Here it is shown that the habitat shift‐related change in selection regime on larval Leucorrhinia caused species in dragonfly lakes to evolve increased larval foraging and activity, and results suggest that they lost the ability to recognise predatory fish. 4. The results of the present study highlight the impact of predators on behavioural trait diversification with habitat‐specific predation regimes selecting for distinct behavioural expression.     

Who eats whom in a pool? A comparative study of prey selectivity by predatory aquatic insects

Predatory aquatic insects are a diverse group comprising top predators in small fishless water bodies. Knowledge of their diet composition is fragmentary, which hinders the understanding of mechanisms maintaining their high local diversity and of their impacts on local food web structure and dynamics. We conducted multiple-choice predation experiments using nine common species of predatory aquatic insects, including adult and larval Coleoptera, adult Heteroptera and larval Odonata, and complemented them with literature survey of similar experiments. All predators in our experiments fed selectively on the seven prey species offered, and vulnerability to predation varied strongly between the prey. The predators most often preferred dipteran larvae; previous studies further reported preferences for cladocerans. Diet overlaps between all predator pairs and predator overlaps between all prey pairs were non-zero. Modularity analysis separated all primarily nectonic predator and prey species from two groups of large and small benthic predators and their prey. These results, together with limited evidence from the literature, suggest a highly interconnected food web with several modules, in which similarly sized predators from the same microhabitat are likely to compete strongly for resources in the field (observed Pianka's diet overlap indices >0.85). Our experiments further imply that ontogenetic diet shifts are common in predatory aquatic insects, although we observed higher diet overlaps than previously reported. Hence, individuals may or may not shift between food web modules during ontogeny.     

Natural born killers: an invasive amphipod is predatory throughout its life-history

Introduced predators can have profound impacts on prey populations, with subsequent ramifications throughout entire ecosystems. However, studies of predator–prey interaction strengths in community and food-web analyses focus on adults or use average body sizes. This ignores ontogenetic changes, or lack thereof, in predatory capabilities over the life-histories of predators. Additionally, large individual predators might not be physically capable of consuming very small prey individuals. Both situations are important to resolve, as native prey may or may not therefore experience ontogenetic or size refuges from invasive predators. Here, we find that the freshwater amphipod invader, Gammarus pulex, is predatory throughout its development from juvenile through to adult. All size classes collected in the field had a common prey, nymphs of the mayfly Baetis rhodani, in their guts. In an experiment with predator, prey and experimental arenas scaled for body size, G. pulex juveniles and adults consumed B. rhodani in all size-matched categories. In a second experiment, the largest G. pulex individuals were able to prey on the smallest B. rhodani. Thus, the prey do not benefit from any ontogenetic or size refuge from the predator. This corroborates with the known negative population abundance relationships between this invasive predator and its native prey species. Understanding and predicting invasive predator impacts will be best served when interactions among all life-history stages of predator and prey are considered.     

Fishing spiders, green sunfish, and a stream-dwelling water strider: male-female conflict and prey responses to single versus multiple predator environments

Many studies have experimentally addressed the effects of a particular predator species on prey behavior. In nature, however, prey frequently face multiple species of predators that often vary in their predatory mode and in their level of predation risk. Relatively few studies have considered prey responses under these complex conditions. In Kentucky, the stream-dwelling water strider (Aquariusremigis) coexists with many potentially dangerous predators, two of which are the green sunfish (Lepomiscyanellus) and the fishing spider (Dolomedesvittatus). Green sunfish occupy stream pools and attack water striders from below. In contrast, fishing spiders hunt along stream shorelines where they perch on overhanging vegetation or rocks and attack water striders near shore. We compared how A. remigis individuals respond to these two very different predators in pools with one or both predators. The presence of sunfish in pools had strong effects on male water strider behavior, including increased use of three types of refuge from sunfish (riffles, climbing out of the water, sitting on the water but at the edges of pools), decreased activity and a decreased number of aggressive males on the water. Spiders also influenced water strider behavior; male water striders avoided spiders by shifting away from the edges of pools. Comparisons of the effects of the two predator species showed that in general, antipredator responses by male water striders were stronger in pools with fish alone than in those with spiders alone. In the presence of both predators, male water strider behavior (microhabitat use and activity) was generally similar to behavior in the presence of fish alone. In contrast, female water striders showed no significant response to the presence of sunfish, and little response to the presence of spiders. This lack of response could be because females spent much of their time in refuges even in the absence of predators (apparently hiding from harassment by males). Both spiders and fish caused decreases in water strider mating activity. The presence of fish reduced both the number of matings per pool (mating frequency), and mean mating durations. Spiders induced a decrease in mean mating duration, but not in mating frequency. The largest reductions in mating activity occurred in pools with both predators present. Pools with either spiders or fish alone suffered 15–20% water strider mortality during our experiment (versus no mortality in predator-free pools). Extant theory suggests that when prey face conflicting microhabitat responses to two predators (as in this study), the predators should have facilitative effects on predation rates (i.e., prey that avoid one predator are often killed by the other and vice versa). Mortality rates in pools with both predators present, however, were not significantly different from that predicted by a null model of multiple predator effects. The lack of predator facilitation can be explained by the compensatory reductions in water strider activity and mating activity in the presence of both predators. Received: 26 August 1996 / Accepted: 12 June 1998     

Predator release of the gastropod <Emphasis Type="Italic">Cyphoma gibbosum</Emphasis> increases predation on gorgonian corals

When large, predatory fishes and invertebrates were excluded from areas of a coral reef in the Florida Keys, USA, densities of the normally rare gastropod Cyphoma gibbosum, a principal predator of gorgonian corals, increased 19-fold. Gorgonians in predator exclosures were grazed more frequently and extensively by C. gibbosum than were gorgonians in uncaged areas. In exclosures, 14% of all gorgonians showed recent predation by C. gibbosum, with 62% of the entire colony surface being removed from these attacked individuals. In areas where predators of C. gibbosum were not excluded, only 5% of gorgonians exhibited recent damage, with only 26% of the colony surface being removed from these few damaged individuals. Thus, the increases in both frequency and extent of attack combined to produce an 8× increase in gorgonian damage following removal of large predators. These patterns suggest that predators typically suppress C. gibbosum populations, that overfishing of these predators could release C. gibbosum from top-down control, and that this release will allow increased damage to gorgonian corals.