Foraging requirements of the endangered long-fingered bat: the influence of micro-habitat structure, water quality and prey type

Myotis capaccinii is one of the most endangered Mediterranean bats. We radio tracked 21 adult individuals to assess foraging range and analyse micro-habitat selection around a nursery roost in central Italy. Habitats were characterized by development of riparian vegetation, distance between banks, degree of water clutter and levels of water pollution (expressed by macro-benthic bioindicators). Diet was also analysed to see whether prey rarity might account for species decline. Myotis capaccinii proved highly mobile: the maximum straight line distance between roost location and the farthest foraging fix recorded on one night was c . 21 km, whereas this variable averaged 7.5 km for the entire study. In general, the species preferred calm waters bordered by well-developed riparian vegetation and large (>5 m) inter-bank distances. Such factors determined the overall quality of foraging sites. Although diet was dominated by pollution-tolerant insects such as Chironomus midges, bats preferred less polluted waters. Our study also confirmed the occurrence of piscivory in this bat. Of the factors potentially responsible for species endangerment, the most likely are general habitat degradation, that is alteration of riparian vegetation and pollution, and cave roost loss. Given the large ecological niche overlap, increasing Myotis daubentonii may be outcompeting M. capaccinii . The most urgent actions to preserve M. capaccinii are extensive restoration of riparian vegetation and strict roost protection. Our study offers indications about where, and how, restoration of riparian vegetation may translate into best conservation results.     

Automimicry and the evolution of discrete prey defences

We consider the neglected question of how secondary defences of prey animals evolve if they are discontinuous in nature, being either present or absent, or expressible over a limited number of levels. We present a novel computer model that evaluates the conditions in which defended mutant prey may (1) fail to rise above nontrivial levels within a population, (2) reach values close to fixation, or (3) find some evolutionarily stable strategy (ESS) frequency between these two situations. Undefended prey that coexist with defended conspecifics are known as automimics. One finding is that automimicry can be an ESS over a range of conditions, but especially when prey are relatively cryptic and secondary defences are very effective at deterring predation. Evolutionarily stable automimicry emerges from the interplay between the direct benefits of costly defences in surviving individual attacks by predators and frequency-dependent benefits conferred on all prey, from a reduction in the rate of attack on all identical-looking prey. When, in contrast, secondary defences have continuous variation, the result is effectively a monomorphic state of defence across the population. Thus the degree and kind of variation that a defence takes has a profound effect on its initial evolution. We discuss the interesting possibility that mixed ESSs may help explain some examples of variation in prey secondary defences.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 393–402.     

The relative influence of prey abundance and co-breeders on the reproductive performance of polyandrous Pale Chanting-goshawks

This study investigates if the reproductive performance of polyandrous Pale Chanting-goshawks, Melierax canorus, is governed by the abundance of dominant rodent-prey species or a co-breeding male participating fully in prey being delivered to the female and young. Polyandrous trios in prey-rich habitat, the only habitat where these trios occurred, failed to produce more offspring than monogamous pairs, but attempted more second broods in years of high prey abundance. The higher the prey-delivering rates at the nesting sites by either one monogamous male or two polyandrous males (combined effort), the higher the proportion of time their females spent in close proximity to the nest. Since there were no significant differences between the body masses of nestlings fledged by polyandrous and monogamous groups, higher delivery rates relieved females from away-from-the-nest hunting duties and permitted them to feed on prey not fed to offspring. Although breeding in polyandrous trios held fitness benefits for females, e.g. to accumulate the necessary body reserves for laying a second clutch in years of high prey abundance, it is still not clear how males benefited. The reproductive performance of each group was strongly linked to the abundance of the dominant, otomyine rodent prey (Otomys unisulcatus and Parotomys brantsii) and it was therefore prey abundance, and not the number of males delivering prey to the female and nestlings at each nesting site, that controlled the reproductive performance of cooperative-breeding Pale Chanting-goshawks.     

Predation,apparent competition,and the structure of prey communities

It is argued that alternate prey species in the diet of a food-limited generalist predator should reduce each other's equilibrial abundances, whether or not they directly compete. Such indirect, interspecific interactions are labeled apparent competition. Two examples are discussed in which an observed pattern of habitat segregation was at first interpreted as evidence for direct competition, but later interpreted as apparent competition resulting from shared predation. In order to study the consequences of predator-mediated apparent competition in isolation from other complicating factors, a model community is analyzed in which there is no direct interspecific competition among the prey. An explicit necessary condition for prey species coexistence is derived for the case of one predator feeding on many prey species. This model community has several interesting properties: (1) Prey species with high relative values for a parameter $\text{r}\text{a}$ are “keystone” species in the community; (2) prey species can be excluded from the community by “diffuse” apparent competition; (3) large changes in the niche breadth of the predator need not correspond to large changes in predator density; (4) the prey trophic level as a whole is regulated by the predator, yet each of its constituent species is regulated by both the predator and available resources; (5) increased productivity may either increase, decrease, or leave unchanged the number of species in the community; (6) a decrease in density-independent mortality may decrease species diversity. These conclusions seem to be robust to changes in the prey growth equations and to the incorporation of predator satiation. By contrast, adding prey refugia or predator switching to the model weakens these conclusions. If the predator can be satiated or switched, the elements a_ij comprising the community matrix may have signs opposite the long-term effect of j upon i. The effect of natural selection upon prey species coexistence is discussed. Unless r_i, K_i, and a_i are tightly coupled, natural selection within prey species i will tend to decrease the equilibrial abundance of species j.     

Temperature and prey density jointly influence trophic and non‐trophic interactions in multiple predator communities

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Subsidies to predators, apparent competition and the phylogenetic structure of prey communities

Ecosystems are fragmented by natural and anthropogenic processes that affect organism movement and ecosystem dynamics. When a fragmentation restricts predator but not prey movement, then the prey produced on one side of an ecosystem edge can subsidize predators on the other side. When prey flux is high, predator density on the receiving side increases above that possible by in situ prey productivity, and when low, the formerly subsidized predators can impose strong top-down control of in situ prey—in situ prey experience apparent competition from the subsidy. If predators feed on some evolutionary clades of in situ prey over others, then subsidy-derived apparent competition will induce phylogenetic structure in prey composition. Dams fragment the serial nature of river ecosystems by prohibiting movement of organisms and restricting flowing water. In the river tailwater just below a large central Mexican dam, fish density was high and fish gorged on reservoir-derived zooplankton. When the dam was closed, water flow and the zooplankton subsidy ceased, densely packed pools of fish formed, fish switched to feed on in situ prey, and the tailwater macroinvertebrate community was phylogenetic structured. We derived expectations of structure from trait-based community assembly models based on macroinvertebrate body size, tolerance to anthropogenic disturbance, and fish-diet selectivity. The diet-selectivity model best fit the observed tailwater phylogenetic structure. Thus, apparent competition from subsidies phylogenetically structures prey communities, and serial variation in phylogenetic community structure can be indicative of fragmentation in formerly continuous ecosystems.     

The influence of habitat homogenization on the trophic structure of fish fauna in tropical streams

Habitat homogenization is one of the most important drivers of change in riverine fauna. Therefore, the aim of this study was to determine whether habitat homogenization influences the trophic structure of fish assemblages in tropical streams. We sampled 78 streams located in pasture and crop lands to examine habitat variables and fish. Principal coordinates analysis, canonical analysis of principal coordinates, and a distance-based test for homogeneity of multivariate dispersions revealed two groups of streams, designated homogeneous and heterogeneous, based on the habitat variables. We determined trophic guilds according to the frequency and biovolume of food items. Seven guilds were identified: aquatic insectivores, terrestrial insectivores, detritivores, herbivores, omnivores, algivores, and detritivores–algivores. Homogeneous streams showed higher abundance and biomass of aquatic insectivores, detritivores, and algivores. Heterogeneous streams showed greater diversity of trophic guilds and higher abundance and biomass of terrestrial insectivores and herbivores than homogeneous streams. Our results demonstrate that trophic structure is influenced by habitat condition. Additionally, the riparian canopy and nearshore vegetation have a modulating role in the trophic structure of stream fishes due to their influence on resource supply and promotion of the physical heterogeneity of the channel.     

The influence of clothing ensembles on the lower critical temperature

This paper describes the effect of clothing insulation on the lower critical temperature (LCT). Twelve young adult females were exposed to a temperature of 10 degrees C for 2 1/2 h. LCT was estimated at five different clothing conditions according to the intersect method. The total weights of clothing ensembles (CW) of the five conditions were 0.45, 0.52, 0.82, 1.34, and 2.56 kg, and their thermal insulating values (I) were 0.44, 0.60, 0.77, 1.21, and 2.14 clo, respectively. LCT of the five clothing ensembles were estimated to be 26.4, 25.4, 23.5, 21.5, and 17.5 degrees C, respectively. The regression equation of the logarithm of LCT on CW was calculated as logLCT = 1.4469-0.08283 CW and that on I was log LCT = 1.4613-0.10526 I, respectively. The rate of changes in LCT is suggested to be dependent on the clothing conditions as for the following equations: dLCT/dCW = -5.34 exp(-0.1907 CW) or dLCT/dI = -7.01 exp(-0.2424 I).     

The effects of prey relative abundance and chemical cues on prey selection in rainbow trout

An optimal foraging model was used to predict prey selection based on both energy maximization and number maximization strategies. The influence of chemical cues and relative abundance on rainbow trout diet selection was examined under laboratory conditions.
In most fish, diet composition was strongly influenced by chemical cues. No fish followed an energy maximization strategy, and selection of prey based on taste persisted despite large caloric penalties associated with these choices. In the absence of chemical cues, diet composition was based on relative abundance of prey (a number maximization strategy). Within the feasible constraints of the optimal foraging model lie a large number of possible diet combinations which would provide sufficient energy for growth and reproduction. This provides a wide scope for feeding flexibility. Response to prey chemical cues may be the basis for observations of individual diet variability in trout.     

Diet and prey selection in the trawling long-fingered bat

The diet of the long-fingered bat Myotis capaccinii is poorly known, and there is no previously recorded information on this species' prey preferences. To investigate these subjects, we captured 51 individuals at a nursery cave in the Iberian Peninsula, from pre-breeding to post-lactation seasons. Each bat's diet composition was assessed by faecal content analysis and its foraging places (rivers, pools and channels) identified by radio-telemetry. To estimate prey availability, we sampled arthropods in the individual bats' identified foraging places and also emulated the bats' hunting technique. The bats' diet comprised of arthropods, dominated by small insects with aquatic larvae and flying adult phases. The most consumed taxon was Nematocera (mainly Chironomidae), including adults and pupae, which were also found to be the most abundant prey over water. Other frequently consumed prey were brachycerans, lepidopterans, arachnids, trichopterans and neuropterans. Diet proportions were compared with prey availability to infer a rank of preferences. The preferred prey were lepidopterans and arachnids, both having a terrestrial life cycle and a bigger size than any other taxa consumed. Without discarding the possible underestimation of prey's aerial availability, the observed preference pattern seems to be a consequence of selection for size more than for specific taxa. Apparently M. capaccinii efficiently exploit water-related prey according to availability when the bats hunt low over the water's surface, and are also able to take more profitable prey found higher in the air.     

The influence of prey hardness on Daphnia's selectivity for large prey

Two comparable methods were used to study the feeding of four species of Daphnia on large spherical particles which differed in size and hardness. The first method used gut analysis to estimate the selectivities of daphnids feeding in a broad size range of a single particle type, including polystyrene beads (4–60 µm diameter) in the laboratory and Eudorina colonies (10–90 µm) in the field. In the second method, Daphnia of different sizes fed in a mixture of 6.5 µm Chlamydomonas and one of eight test particles. Smaller daphnids were less effective in feeding on large test particles. Nonlinear regression was therefore used to estimate the Daphnia body size at which the clearance rate on a test particle was reduced to 50% of that for Chlamydomonas. The results of both methods show that prey size and hardness are both very important in determining daphnid feeding selectivity. For a given particle size, soft algae (naked and gelatinous flagellates) are more readily ingested than hard algae (diatoms and dinoflagellates), and hard algae are more readily ingested than polystyrene beads. Daphnia can feed effectively on algae that are 2–5 times larger than the largest ingestible bead.     

The influence of prey behaviour on prey selection of the carnivorous plant Utricularia vulgaris

The mechanisms underlying differential prey selection of two microcrustaceans by the common bladderwort (Utricularia vulgaris) were studied in the laboratory. Functional response experiments with single prey showed that Utricularia had a higher attack rate coefficient and a longer handling time coefficient with the cladoceran Polyphemus pediculus than with the cyclopoid copepod Eucyclops serrulatus. Observation of predation rate, defined as number of prey eaten per unit time, from direct behavioural observation on single prey species, showed a higher predation rate with Polyphemus than on Eucyclops, at low prey densities. The opposite pattern was found at high prey density. When the two prey were presented simultaneously to the predator, Eucyclops was preferred over Polyphemus. Results from the situation with two prey and some of the results from the direct behavioural observations support field data on the diet of Utricularia, which shows that cyclopoid copepods are selected more frequently than Polyphemus.     

The influence of trophic status and large-scale climatic change on the structure of fish communities in Perialpine lakes

1. A recurrent question in ecology is the influence of environmental factors, particularly nutrients and climatic variables, on community structure and functioning, and their interaction with internal community processes (e.g. competition). 2. Perialpine lakes have been subject to two main kinds of human-induced changes over the last 50 years: eutrophication-reoligotrophication, represented by lake-specific changes in total phosphorus concentration (TP), and long-term global climatic change, captured by average winter temperature (AWT). 3. Changes in fish communities (abundance of seven species from fishery data) in 11 Perialpine lakes during 31 years (1970-2000) were investigated in relation to variation in TP and AWT using models incorporating the effects of fish maturation age, and potentially discriminating effects on adult survival and recruitment. 4. We show that phosphorus concentration affects fish abundance in species-specific ways. These effects are mediated by recruitment rather than by adult survival. Phosphorus effects are probably modulated by interspecific interactions, as increasing TP enhances total community biomass, which in turn is either positively or negatively associated with species abundance depending on species position in trophic chains. 5. Climatic change has very little effect on fish abundances, which is not consistent with the prediction of larger changes in species near their southern distribution boundary. 6. We propose several hypotheses to account for those findings, and place our study in the wider framework of community ecology.     

The evolution of trophic structure

The trophic relationships of an ecological community were represented by digital individuals consuming resources or prey within a simulated ecosystem and producing offspring that may differ from their parents. When individuals meet, a few simple rules are used to decide the outcome of their interaction. Trophically complex systems persist for long periods of time even in finite communities, provided that the strength of predator-prey interaction is sufficient to repay the cost of maintenance. The topology of the food web and important system-level attributes such as overall productivity follow from the rules of engagement: that is, the macroscopic properties of the ecosystem follow from the microscopic attributes of individuals, without the need to invoke the emergence of novel processes at the level of the whole system. Evolutionarily stable webs exist only when the pool of available species is small. If the pool is large, or speciation is allowed, species composition changes continually, while overall community properties are maintained. Ecologically separate and topologically different source webs based on the same pool of resources usually coexist for long periods of time, through negative frequency-dependent selection at the level of the source web as a whole. Thus, the evolved food web of species-rich communities is a highly dynamic structure with continual species turnover. It both imposes selection on each species and itself responds to selection, but selection does not necessarily maximize stability, productivity or any other community property.     

The influence of preformed defences on the dynamic wound response in Spruce bark

1. Two of the principal defences in conifer bark against attack by bark beetles and associated fungi, the flow of preformed resin and the dynamic wound response (DWR), are commonly regarded as separate, sequential responses to attack. In this paper the concentration of three preformed defences (resin, total polyphenols and lignified stone cell masses) was measured at different heights on the stem of Norway and Sitka Spruce to determine their effect on the size of lesions formed during the DWR to inoculation with three facultatively pathogenic fungi ( Phacidium coniferarum, Ophiostoma piceae and Cryptosporiopsis sp.) inoculated during the dormant season.
2. There was considerable within-tree variation in concentration of lignin and there was a dose-dependent negative effect of lignin on lesion size. The form of the relationship, however, was influenced by fungal and tree species and for some fungi, also by an individual tree effect.
3. Results suggest that resistance of conifer bark to pests and pathogens depends on an interaction between preformed and induced defences.     

On competition of predators and prey infection

A class of prey–predator models with infected prey is investigated. Predation terms are either of Holling type II or III, infection is either modelled by mass action or standard incidence. It is shown that the key for understanding the model behaviour is the competition of predators versus infection. In the presented models the predator is not susceptible to the infection and the infection of the prey has no influence on the ability of the predator of catching the prey. However, the prey population can be seen as a resource which both the predators and the infection depend on. The competition for this resource is strong—the principle of competitive exclusion holds for biologically meaningful choices of parameters as long as there is no destabilisation by a Hopf bifurcation. The representation of models in competition diagrams which are introduced in this article can be used for a wide range of competition models which seems to be a promising method with many potential applications.     

The influence of prey identity and size on selection of prey by two marine fishes

Laboratory experiments were conducted with two predatory fishes, Lagodon rhomboides (Linnaeus) and Syngnathus floridae (Jordan & Gilbert), to determine if prey selection was a result of predator preference or prey accessibility. Prey consisted of two species of caridean shrimp, Tozeuma carolinense (Kingsley) and Hippolyte zostericola (Smith), that commonly inhabit seagrass meadows. Natural diets of both predators revealed that selection ofTozeuma and Hippolyte was not related to their field densities. My experiments demonstrated that natural prey selection was a consequence of prey accessibility, not predator preference. Experiments examining the role of prey size in predator preference revealed that large individuals were significantly preferred over small individuals. Observations of prey behavior indicated that prey motion affected predator choice. These results suggest that predator preference was primarily determined by prey visibility and that the combined effects of prey size and motion contributed to the visibility of these prey.     

Predatory wasps learn to overcome the shelter defences of their larval prey

Larvae of Epargyreus clarus (Hesperiidae), the silver-spotted skipper, inhabit leaf-and-silk shelters that they construct on their leguminous host plants. In the field, Polistes spp. (Vespidae) wasps land on the shelters, quickly extracting and killing the larvae within. In marked contrast, wasps that emerge from field-collected colonies maintained in the laboratory visit and examine leaflets bearing sheltered caterpillars, but only rarely do they extract and kill the sheltered larvae. To examine whether learning is involved in the development of the ability of Polistes wasps to forage successfully on sheltered E. clarus larvae, we tested the responses of P. fuscatus and P. dominulus wasps to sheltered E. clarus larvae before and after their exposure to unsheltered larvae that were visible either on an opened host-leaf shelter (P. fuscatus and P. dominulus) or on a nonhost leaf in the absence of a shelter (P. fuscatus). After killing and processing an unsheltered larva that was visible on an opened leaf shelter, a majority of foragers subsequently extracted and killed larvae from closed shelters. Wasps that killed and processed an unsheltered larva on a nonhost leaf, on the other hand, generally did not later open shelters. Thus, it seems that experience with an exposed larva in the context of its shelter is necessary for a wasp to be able to prey on sheltered larvae. We conclude that the wasps must learn to associate the taste of the larva with shelter-related cues, such as presence of leaf damage and silk. In nature, this initial exposure may occur when the larva is visible in or near its shelter, perhaps when feeding or constructing a new shelter. Learning opportunities will thus depend on larval density. Our results show that invertebrate predators can learn to overcome their prey's defences, and are therefore able to make use of previously inaccessible prey.