Mobile Predators Research Articles

Predation upon Laternula elliptica (Bivalvia, Anatinidae): A field manipulation in South Bay, Antarctica

The presence of empty shells of Laternula elliptica that provide refuge sites for juvenile fishes on the soft-bottom surface of South Bay, Antarctica, has been difficult to explain because this bivalve normally lives deeply buried (>50 cm). L. elliptica individuals unburied and aggregated at the surface by the action of icebergs could be consumed by mobile predators. This paper examines experimentally both burying rates and predation upon unburied L. elliptica in the field at South Bay. Live and intact L. elliptica were hand-collected by diving, and separated in 16 groups of 10 each, and placed on mud-sand bottoms protected from the ice disturbance at a depth of 17 m in South Bay. Eight groups were confined by open wooden frames so as to exclude predators, mainly star-fish and gastropods, the other eight remained as control. Species and number of predators and burying rates were estimated during 23 days. Within the first 24 h, 30% of the bivalves buried themselves, after which, rates fell abruptly. By the end of the day 23, only 60% had successfully buried; of the 40% which remained unburied, 20% were consumed by the following sequence of predators: Odontaster validus, Cryptasterias turqueti, Parborlasia corrugatus, Neobuccinum eatoni and two species of amphipods; all completely consumed one bivalve in 5–7 days. The 20% that remained unburied constituted potential prey though they showed no signs of being attacked by O. validus during the observation period. In addition to serving as prey, L. elliptica provides empty and intact shells used as refuge sites by juvenile fishes.

Prey Selection by Freshwater Predators with Different Foraging Strategies

We observed several freshwater predators, including the odonate larvae Pachydiplax longipennis and Anax junius, the hemipterans Notonecta unifasciata and Buenoa scimitra, the dytiscid larva Acilius semisulcatus, and juvenile Gambusia affinis, feeding on a variety of microcrustacean prey and determined the frequency of the component parts of predator–prey interactions (encounter, attack, capture, ingestion). Encounter rates were the most important determinant of predator selectivity when predators were presented with a variety of microcrustacean prey. When only copepod species were used as prey, however, both encounter rates and capture success were important in determining predator diets. We used our data to test hypotheses concerning relationships between predator foraging mode and patterns of prey selection: mobile predators exhibited stronger selection for sedentary prey than did sit-and-wait predators; our own and literature data also indicated that macroinvertebrate sit-and-wait predators are better able to capture, and have higher selectivity for evasive prey than do mobile predators. A predator's attack acceleration, however, may be a better predictor of its selectivity for evasive versus nonevasive prey than its mean swimming speed.

Niche separation within the mobile predator guild on marine shallow soft bottoms

Segregation of coexisting predatory fish and shrimp species on marine shallow soft bottoms was studied in the Gullmar Fjord (Sweden). Here, the gobiids Pomatoschistus minutus (Pallas) and P. microps (Krayer) and the brown shrimp Crangon crangon L. are the most abundant epibenthic species close inshore. A temporary reduction in number of one of the species was balanced by an increased recruitment of other species in the guild, so that the overall density of epibenthic predators was kept at approximately the same level. Experimental validation of field results showed that segregation maintained by interspecific territoriality is an important mechanism regulating guild structure. We argue that competitive relations undoubtedly are of importance in maintaining structure of the epibenthic communities in Gullmar Fjord, but of minor importance for overall density of the guild.

Crab Response to Prey Density Can Result in Density-Dependent Mortality of Clams

Field experiments involving recovery of marked clams showed that even adult native littleneck clams (Protothaca staminea) could suffer high mortality to cancrid crabs. The mortality rate increased with clam density, suggesting that these crabs preferentially forage in areas of higher prey density. Acoustic telemetry showed that at least one of the crabs, Cancer productus, is sufficiently mobile to search large areas while foraging. This is important for understanding the effects that these large, mobile predators have on the distribution and the abundance of their prey and may explain the high incidence of crab predation seen in mariculture operations where the density of clams is artificially raised.

The Behavioral Response Race Between Predator and Prey

On tente de preciser par la methode de regression lineaire ce qui determine les rapports de force relatifs en ce qui concerne les relations predateur-proie (on donne comme exemple Notonectidae-Culicidae)

Opportunity-Cost Foraging Models for Stationary and Mobile Predators

A simple graphical technique is presented. It relates two existing foraging models to marginal valuations of the time and energy currencies used as proxies for fitness. For anthropologists it is also capable of relating these proxy currencies to utility or preference. The predictions of the models are responsive to important theoretical assumptions of evolutionary ecology research: costs in behavioral trade-offs are opportunity costs, often evaluated at the margin. The approach offers a flexible and potentially subtle method of analyzing foraging behavior of both stationary and mobile foragers. It leads to extension of some existing hypotheses about stationary predators, and it refines existing hypotheses about mobile, searching predators.

Mobile Predators and the Structure of Marine Intertidal Communities

Mobile Predators and the Structure of Marine Intertidal Communities

Flux in the sublittoral macrobenthos of Moreton Bay

AbstractSeveral different intertime dissimilarity measures, used with a variety of standardisations of data, were applied to transformed data of macrobenthic species at six sites. These data were obtained over twenty‐two times at 8‐week intervals. Results were evaluated by stepwise regressions (linear, annual cyclical, longer term cycles). Manhattan metric flux between consecutive times was preferred for most subsequent purposes. This flux divided into positive and negative components which measure, summated over all species, rates of recruitment and depletion. Use of algebraic and absolute sums permits evaluation of an index of homeostasis which measures the counterbalancing of recruitment by some species and depletion by others; this index had a value of ca 0.7.Use of the Manhattan metric with catch standardized data indicated changes of community composition at the (more coastal) Bramble Bay sites with a roughly 3‐yr cycle and at the (more oceanic) Middle Banks sites with a roughly 51/2‐yr cycle.In the main analyses, sites were considered individually and in various groupings. It was shown that at Bramble Bay the optimum near‐annual periodicity gives a 50‐instead of a 52‐week year, and also that with increased numbers of sites in a grouping, the greater the significance of the near‐annual cycles.An hypothesis is outlined involving ‘counterbalancing’ between sites of depletion rates due to mobile predators or ‘disturbers’ (fish and prawns). The counterbalancing of recruitment rates is linked to depletion, and is in line with Caswell's (1978) somewhat theoretical paper in which he suggested the temporary action of predation opens up new cells for colonization.This hypothesis goes far towards ‘explaining’ the known patchiness of benthos in Moreton Bay. Also if mobile predators are a link between areas in proximity with different biotas the ecological unit (2 ‘community’) is necessarily expanded.

Predation on aphids in California's alfalfa fields

Alfalfa fields in two climatically different regions were sampled for aphids and their natural enemies throughout 3 years (1957-1959). The fields were under an integrated control program and therefore received minimum amounts of insecticides. The four imported parasites of the spotted alfalfa aphid and the pea aphid were not yet important in the study area, so predators were mainly responsible for the high degree of naturally occurring biological control. By pooling the data of entire regions, it was possible to follow changes in populations of these mobile predators more accurately than is possible from surveys of single fields because short-distance migration resulting from harvesting practices as well as uneven distribution could be neglected. Coccinellids and hemerobiids, two oligophagous groups, were closely linked in a density-dependent fashion to the aphid populations. This is a good indication that these predators (especially the lady beetles) are able to control the aphids. The more polyphagous predators, the chrysopidae and Hemiptera, become important in the control of the aphids only when the dominant coccinellids are inactive because of diapause or when lack of aphids for reproduction prompts the beetles to leave the fields. When aphid development exceeds the lady beetles’ momentary capacity for increase, however, syrphids are able to take a large toll. Furthermore, several species having similar biologies were found to replace each other throughout the year. Finally, the phenologies of the species could be explained by their biologies (diapause, temperature thresholds, ovipostional behavior).

On the Theory of Optimal Diets

Using techniques of stochastic theory, I develop a new aproach to predicting optimal diets. The models developed are for a mobile predator feeding on stationary prey; however, the models can easily be extended to include mobile prey. Parameters used in the models are caloric content, time to pursue and density of each prey type, and the speed of the predator. Both clumped and random prey distribution are considered. The models predict the optimal diet of a predator faced with a variety of potential prey types. The optimal diet is predicted as the set of successive prey choices which maximizes the rate of caloric intake or, alternatively, minimizes the time required to find a food ration. Also predicted are the criteria for specialization and switching from a specialist diet to a generalist diet. The criteria for specialization and for switching are independent of the density of the alternate prey type. Also, a predator feeding so as to maximize the rate of caloric intake should take a prey on every encoun...

Seed Predation by Animals

Many plants suffer very heavy preand/or post-dispersal seed predation by animals. A few exemplary studies (2,18,38,52,74,87, 106, 110, 111, 124, 140, 161, 162, 171, 181, 187, 196, 197, 203, 205, 207, 217, 220, 227) and a variety of shorter reports scattered through the agricultural, botanical, and zoological literature suggest a large and important, yet unexploited, field of study. It is clear that the pattern of seed predation is highly structured and that it co evolved at, the chemical, spatial, and temporal level. It involves all levels of animal-plant interaction from the internal energy budget of indi­ viduals to the entire community (203 ) . Owing to parental and sibling com­ petition, successful development of a seedling may depend on the seed's dis­ persal (101). Equally important, thc seed must escape from the predators at the seed crop and in the parent plant's habitat before and after dispersal (111 ) . The game is played by mobile predators in search of sessile prey; escape is through a single dispersal move, seed chemistry, parental morphol­ ogy and behavior, and evolutionary change. The processes and patterns are:ideal candidates for ecological and evolu­ tionary analyses (83, 111 ) of the typcs traditionally conducted by zoologi­ cally oriented biologists (37, 51,73, 141, 155,156, 182) or applied to plants in general ( 40,116,208,209,241) . Seed predators and leaf eaters are often lumped together in ecological discussions, but they differ in ways especially important in the coevolution of seed predators and seeds: (a) Like leaves, seeds are highly subdivided and small, but unlike leaves and other vegetative parts, they have very high nutrient values per unit volume. ( b) While obvious in large quantities, they may be extremely inconspicuous once dispersed. ( c) Being comparatively dormant, seeds have low self-repair abilities but can contain high concentra­ tions of toxic compounds (secondary substances) with less sophisticated ad­ aptations against self-intoxication than can leaves and meristematic tissues. ( d ) Seed production is not continually required for direct survival of the parent plant; seed timing, quantity, and quality can therefore be manipu­ lated more freely by natural selection than can these traits of leaves and other vegetative parts. (e ) Seeds are not directly replaced· when killed or germinated; once removed, seeds may be absent far longer than edible vege­ tative parts and thus a common plant species may be rare in time,toa seed

The Limiting Effects of Natural Predation on Experimental Cotton Rat Populations

Survival curves for 2to 6-month periods were plotted for 17 different populations of nonbreeding cotton rats (Sigmodon hispidus) introduced into isolated or enclosed areas of natural habitat. Eight populations were introduced onto predator-free islands or into a 1-acre, predator-proofed enclosure of old field habitat, and nine populations were released into 1-acre enclosures freely accessible to bird and mammal predators. Radioactive pins (cobalt-60 or zinc-65) inserted under the skin aided in determining the fate of cotton rats which failed to appear in live traps. Survival curves were linear or convex for introduced populations protected from predation and strongly concave for those open to natural predators. Abundant evidence for kills by hawks, foxes, and bobcats was found in the latter cases. A density of about 15/acre, the mean point of inflection in the survival curves, was considered to be a predator-limited carrying capacity since mortality was high above, and low below, this density when predators were active. The experimental study has special relevance to the fall and winter cotton rat populations in the southeastern United States. It is concluded that when diverse and highly mobile predator populations are present they are more important than food, social interaction, or weather in regulating cotton rat density. The role played by predation in the regulation of mammal populations is usually difficult to determine because survival of individuals and the exact causes of mortality are hard to ascertain in the field. Isolated or enclosed areas of natural habitat can simplify the evaluation of predation effects since emigration and immigration can be controlled and the survival of marked individuals can be followed with reasonable precision. The object of this investigation was to determine the effect of natural predation on the mortality of nonreproducing populations of the cotton rat confined to areas of natural habitat. Survival of groups of animals introduced to predatorfree islands and to a large predator-proof enclosure was compared with survival of similar groups occupying enclosures accessible to predators. In all, survival curves for 2to 6-month periods were plotted for 17 different populations. I am especially indebted to Drs. Eugene 1 Contribution from the Laboratory of Ecology, AEC Savannah River Plant supported by AEC Contract No. AT(38-1)-310. 2Present address: Tall Timbers Research Station, Tallahassee, Florida. 698 P. Odum and Frank B. Golley for help in organizing the manuscript; Drs. Richard G. Wiegert and Michael H. Smith also read the manuscript and gave helpful suggestions. John H. Harper and Dr. George F. O'Neill of AEC Savannah River Plant assisted with radionuclide labeling and John B. Gentry, Jim C. Mayenschein, Michael R. Pelton, and Dr. Howard Orr assisted in the field. Dr. Orr also permitted me to use his unpublished data to construct curve No. 4 (Fig. 8).

Studies on Avian Predators of Dendroctonus brevicomis LeConte (Coleoptera: Scolytidae) With Special Reference to Picidae

AbstractFour species of woodpeckers (family Picidae) are definitely known to be predaceous on the western pine beetle in the Central Sierra Nevada Mountains in California. These are: Dendrocopus villosus, Dendrocopus pubescens, Dendrocopus albolarvatus and Dryocopus pileatus. The red-shafter flicker (Colaptes cafer, Picidae), creepers (Certhiidae), nuthatches (Sittidae), and flycatchers (Tyrannidae) are thought to be predators on the western pine beetle.Predation by woodpeckers reduced the western pine beetle population by (a) actual consumption of 31.8% in two generations studied, and (b) by increasing parasite densities in the order of 3.85 factor. The increase in parasite density was believed to have been caused by bark removal to a near uniform thickness enabling a higher parasitism by those parasites with short ovipositors, such as Cecidostiba and Roptrocerus spp.One adverse effect of woodpecker predation was a reduction or a depression of insect predation. Highly mobile insect predators may have been driven away by woodpecker activity, actually consumed, or both.Bark flakes, chipped or pried off by the woodpeckers during their feeding activity, contained but few insects and it is doubtful that these could survive on the ground and reach the adult stage.