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PubMed1993

Small and medium sized mammals as predators of ticks (Ixodoidea) in South Africa.

A total of 1,640 stomach contents from 56 South African species of small and medium sized mammals were examined for ticks. Only six ticks were found in three specimens of the caracal Felis caracal. Although identification of the tick species was not possible owing to fragmentation and partial digestion, the genus Haemaphysalis was represented in four of these cases. We conclude that predation by small and medium sized mammals on ticks is uncommon in South Africa.

Animals↗
PubMed2004

Web-building spiders attract prey by storing decaying matter.

The orb-weaving spider Nephila edulis incorporates into its web a band of decaying animal and plant matter. While earlier studies demonstrate that larger spiders utilise these debris bands as caches of food, the presence of plant matter suggests additional functions. When organic and plastic items were placed in the webs of N. edulis, some of the former but none of the latter were incorporated into the debris band. Using an Y-maze olfactometer, we show that sheep blowflies Lucilia cuprina are attracted to recently collected debris bands, but that this attraction does not persist over time. These data reveal an entirely novel foraging strategy, in which a sit-and-wait predator attracts insect prey by utilising the odours of decaying organic material. The spider's habit of replenishing the debris band may be necessary to maintain its efficacy for attracting prey.

Animals↗
PubMed2005

Larval competition in weevils Revena rubiginosa (Coleoptera: Curculionidae) preying on seeds of the palm Syagrus romanzoffiana (Arecaceae).

Inter- and intraspecific local resource competition may lead to the selection of specific adaptive individual characteristics to overcome interference competition. A highly selective scenario is predictable for interference competition among seed preying weevil larvae that live in and feed upon a single host seed. This scenario is found in Syagrus romanzoffiana palm seeds which are predated by Revena rubiginosa (Curculionidae) larvae. Although multiple infestation of one seed by weevil larvae can occur, invariably only one individual survives and develops in each host seed. A strong competition between the first instar larvae in a restricted window of host fruit development stages leads to physical interactions of conspecifics by ovicide or direct fighting using falcate mandibles. The occurrence of this type of mandible is synchronized with fruit development and restricted to instars with probable competition, as infestation occurs only while the endocarp is soft. Only after lignification of the endocarp the larva changes into the next instar. Mandibles of subsequent instars differ markedly from those of the first instar. The new mandibles can scrape the solid endosperm but are unable to perforate and kill conspecifics. These findings give strong evidence for the selective pressure of intraspecific competition, where special behaviour, mandible morphology and synchronization of its changes with the seed development contribute to individual benefit that involves the killing of conspecifics, since one host seed can only maintain a single larva throughout its complete development.

Animals↗
PubMed2004

Rodents balancing a variety of risks: invasive fire ants and indirect and direct indicators of predation risk.

We used foraging trays to compare how oldfield mice, Peromyscus polionotus, altered foraging in response to the presence of fire ants, Solenopsis invicta, and in the presence of direct (predator urine) and indirect (sheltered or exposed microhabitat, moonlight, and precipitation) indicators of predation risk. Foraging reductions elicited by S. invicta were greater than reductions in response to well-documented indicators of risk (i.e., moonlit nights) and the presence of predator urine. The presence of S. invicta always led to reduced foraging, but the overall impact of S. invicta was dependent upon microhabitat and precipitation. When S. invicta was not present, foraging was greater in sheltered microhabitats compared to exposed microhabitats. S. invicta made sheltered microhabitats equivalent to more risky exposed microhabitats, and this effect was especially pronounced on nights without precipitation. The effect of S. invicta suggests that interactions with S. invicta may entail a potentially heavy cost or that presence of S. invicta may represent a more reliable indicator of imminent competition or predation compared to indirect cues of risk and predator urine. The presence of S. invicta led to reduced foraging under situations when foraging activity would otherwise be greatest (i.show $132#e., under vegetative cover), potentially reducing habitat quality for P. polionotus and the distribution of seeds consumed by rodents.

Analysis of Variance↗
PubMed2005

Mechanisms of selectivity in a nocturnal fish: a lack of active prey choice.

Fish that feed on individual zooplankton usually exhibit strong selectivity for large prey. Such selectivity can result from the predator's active choice of larger prey or from differential encounter rate due to lower detectability of small prey, or both. In diurnal fishes, selectivity is thought to be determined mostly by active choice. In spite of a lack of direct observations, active choice is also considered the prevailing mechanism of prey selectivity in nocturnal fishes. Our objective was to resolve this mechanism in the highly selective, nocturnal zooplanktivorous fish Apogon annularis. Laboratory experiments indicated that the fish's encounter rate with small prey was lower than that with large prey and that its selectivity became stronger with decreasing light intensity. Feeding efficiency, defined as the ratio between feeding and encounter rates, ranged 41-89% and was positively correlated with prey size. When feeding on a mixture of prey sizes, the fish fed on each size group at a rate similar to that of its feeding on the respective size alone, indicating that selectivity in A. annularis was due to size-dependent encounter rate and differential feeding efficiency. A low visual acuity in A. annularis, as inferred from its inability to detect small prey (<0.9 mm in length), together with the low abundance of large zooplankton in situ, can explain the dominance of differential encounter over active choice in this nocturnal coral-reef fish.

Animals↗
PubMed2006

Reproductive tactics under severe egg predation: an eider's dilemma.

Parental defence against predators may increase offspring survival but entail other costs. Egg predation is frequent early in the laying sequence of the common eider, which differs in this and in several other ways from most other waterfowl. We test the hypothesis that permanent presence at the nest from the second or third egg is an adaptation for reducing egg predation in eiders. Two other alternative hypotheses for lower predation at later nest stages are early predation loss of the most vulnerable nests and seasonal decrease in predation risk. Analyses of predation rates at the one-egg and later stages refute these two alternatives. Early nest attendance by eider females is estimated to increase clutch survival by about 20% in four-egg and 35% in five-egg clutches, albeit probably at a cost of smaller clutch size.

Animals↗
PubMed2006

Hierarchical patch dynamics and animal movement pattern.

In hierarchical patch systems, small-scale patches of high density are nested within large-scale patches of low density. The organization of multiple-scale hierarchical systems makes non-random strategies for dispersal and movement particularly important. Here, we apply a new method based on first-passage time on the pathway of a foraging seabird, the Antarctic petrel (Thalassoica antarctica), to quantify its foraging pattern and the spatial dynamics of its foraging areas. Our results suggest that Antarctic petrels used a nested search strategy to track a highly dynamic hierarchical patch system where small-scale patches were congregated within patches at larger scales. The birds searched for large-scale patches by traveling fast and over long distances. Once within a large-scale patch, the birds concentrated their search to find smaller scale patches. By comparing the pathway of different birds we were able to quantify the spatial scale and turnover of their foraging areas. On the largest scale we found foraging areas with a characteristic scale of about 400 km. Nested within these areas we found foraging areas with a characteristic scale of about 100 km. The large-scale areas disappeared or moved within a time frame of weeks while the nested small-scale areas disappeared or moved within days. Antarctic krill (Euphausia superba) is the dominant food item of Antarctic petrels and we suggest that our findings reflect the spatial dynamics of krill in the area.

Animal Migration↗
PubMed2005

Patterns of avian nest predators and a brood parasite among restored riparian habitats in agricultural watersheds.

In fragmented edge-dominated landscapes, nest predation and brood parasitism may reduce avian reproductive success and, ultimately, populations of some passerine species. In the fragmented agroecosystem of northwest Mississippi, placement of drop-pipe structures has been used as a restoration technique for abating gully erosion along stream banks. These actions have formed small herbaceous and woody habitat extensions into former agricultural lands. We quantified species relative abundances, species richness, and evenness of avian nest predators and a brood parasite within four categories of constructed habitat resulting from drop-pipe installation. Differences in the abundance of two nest predators, cotton mouse (Peromyscus gossypinus) and blue jay (Cyanocitta cristata), were observed among constructed habitats. However, relative abundances of other predators such as common grackle (Quiscalus quiscula), American crow (Corvus brachyrhynchos), and hispid cotton rat (Sigmodon hispidus), and the obligate brood parasite brown-headed cowbird (Molothrus ater) did not differ among four habitat categories. Although species richness, abundance, and evenness of potential nest predators were generally similar among the constructed habitats, predator species composition varied, suggesting that these habitats supported different predator communities. This difference is important because as each predator species is added to or deleted from the community, variation may occur in the framework of prey search methods, predator strategies, and potentially overall predation pressure. We suggest that land managers using drop-pipes as part of stream restoration projects allow for the development of the constructed habitat with the largest area and greatest vegetative structure.

Agriculture↗
PubMed1985

Parturition influences initial pup preferences at later onset of maternal behavior in primiparous rats.

Initial maternal responsiveness as a function of varying pup stimuli was assessed in primiparous Long-Evans rats. Pups were removed during parturition and the dams tested beginning 24 hr later. These dams were most likely to respond maternally towards newborn (0-2-day-old) rat pups (100%) and 6-8-day-old hamsters, which are the size of newborn rats (83.3%). In contrast, dams were significantly less likely to respond maternally towards newborn hamsters (50%) and 8-10-day-old rats (16.7%), pups which are half as large and twice as large, respectively, as newborn rats; indeed, dams were likely to attack these pups (33.3% and 25%, respectively). The maternal response (less than or equal to 1 hr) to dead newborn rats was similar to that towards live newborn rats, except that fewer dams retrieved dead pups rapidly (less than or equal to 1 min). Cesarean-delivered dams did not display higher maternal responsiveness towards 0-2 than towards 8-10-day-old rats. Further, whereas no parturition-experienced dam displayed infanticide towards newborn rats, 21.9% of primiparous Cesarean-delivered dams did. Thus, the exogenous and/or endogenous stimuli associated with parturition enhance selective maternal responsiveness and diminish infanticide towards pups the size of newborn rats.

Aggression↗
PubMed2005

Spatial variation of mercury levels in nesting Bonelli's eagles from Southwest Portugal: effects of diet composition and prey contamination.

Mercury (Hg) was determined in adult Bonelli's eagles (Hieraaetus fasciatus) and their avian prey, from samples of feathers collected between 1992 and 2001 at the nesting sites of 21 pairs in Southwest Portugal. Eagle Hg levels showed great variation, reflecting primarily differences in diet composition and food chain biomagnification. Concentrations were positively correlated with the dietary proportion of insectivorous and omnivorous birds (e.g. egrets, corvids and thrushes), with very low levels for pairs feeding mainly on herbivores (e.g. rabbits, pigeons and partridges). Differences in prey contamination among breeding territories added to dietary effects in determining variation of Hg levels in eagles, shaping a spatial pattern that was largely consistent with a source of contamination in a coal-burning power-plant lying upwind of the study area. Despite this presumed contamination, Hg levels seemed to be of little concern to this eagle population, though there might be subtle deleterious effects on the reproductive output of a few pairs. This study emphasizes the need to account for dietary effects when biomonitoring Hg contamination using birds of prey.

Animals↗
PubMed2002

The venom optimisation hypothesis: a spider injects large venom quantities only into difficult prey types.

The spider Cupiennius salei needs 0.01-10 microl venom to kill a prey item. Since its venom glands contain only 10 microl and regeneration requires 8-16 days C. salei should use its venom very economically. By a monoclonal antibody we measured, for the first time, the amounts of venom injected by a spider into different prey types. Crickets and stick insects, as victims without special defence mechanism, received only the minimum amount of venom which is not significantly different from the LD(50). Blowflies and ground beetles received considerably more venom because they are difficult to overwhelm or even endanger the spider by their defence behaviour. These results support our venom optimisation hypothesis which supposes that spiders use their venom as economically as possible.

Animals↗
PubMed2001

Energetic and physiological correlates of prey handling and ingestion in lizards and snakes.

In this review, we summarize the energetic and physiological correlates of prey handling and ingestion in lizards and snakes. There were marked differences in the magnitude of aerobic metabolism during prey handling and ingestion between these two groups, although they show a similar pattern of variation as a function of relative prey mass. For lizards, the magnitude of aerobic metabolism during prey handling and ingestion also varied as a function of morphological specializations for a particular habitat, prey type, and behavior. For snakes, interspecific differences in aerobic metabolism during prey handling seem to be correlated with adaptations for prey capture (venom injection vs. constriction). During ingestion by snakes, differences in aerobic metabolism might be due to differences in cranial morphology, although allometric effects might be a potentially confounded effect. Anaerobic metabolism is used for prey handling and ingestion, but its relative contribution to total ATP production seems to be more pronounced in snakes than in lizards. The energetic costs of prey handling and ingestion are trivial for both groups and cannot be used to predict patterns of prey-size selection. For lizards, it seems that morphological and ecological factors set the constraints on prey handling and ingestion. For snakes, besides these two factors, the capacity of the cardio-respiratory system may also be an important factor constraining the capacity for prey handling and ingestion.

Animals↗
PubMed2002

Overview: For crying out loud--dangers and opportunities of communicating in the public domain.

Communication often extends into the public domain, inviting "eavesdropping" and other forms of exploitation by other species. Conflict is frequently the result, although interspecific communication can be mutually beneficial even when interests conflict fundamentally, such as between predator and prey. However, the most complex communication systems are likely to involve species with mutual rather than with conflicting interests. When interests do conflict, exploitation of the communication systems of others may impose high costs on signalers and select for signals that are less exploitable. Other costs of communication in the public domain arise from "mistakes" (e.g., mating with the wrong species) and select for more species-specific signal structure. The articles in this section illustrate the complexity of interspecific communication and yield important insights into the dynamic nature of communication systems.

Agonistic Behavior↗
PubMedDate not supplied

Flock-feeding on fish schools increases individual success in gulls.

Flock-foraging and the role of white plumage in gulls and other seabirds have been the subject of much debate. At first sight it seems that competition within the flock would render flock formation against the interest of the bird who finds the fish school, as the fish must then be shared with birds joining the flock. However, it is also possible that flock formation is neutral or even beneficial to the individual members, including the bird that found the fish (the 'first finder'). Here we show that the fishing success of individual black-headed gulls, Larus ridibundus, increases with flock size up to at least eight birds. Part of the reason is that the fish school is more vulnerable when attacked by several gulls. The first gull to reach a fish school therefore benefits from being joined by others, and conspicuous white upper parts in gulls may act as a means of attracting other gulls to the flock and hence improving hunting success.

Animals↗