Relative Prey Size Research Articles

Decreased reproductive rate of the spider, Nephila clavata, inhabiting small woodlands in urban areas

AbstractThe reproductive characteristics and feeding conditions of the spider, Nephila clavata, were examined at some urban and non‐urban woodland sites. More than 80% of females were gravid by late October in both non‐urban and large urban woodlands, whereas only 10%–30% were gravid in small urban woodlands. The expected number of eggs per female in mid‐October was also lower in the small urban woodlands, although body length was not reduced. This suggests that reproductive failure was not caused by food shortage during the nymphal stage. Relative food consumption rate, prey size, biomass and size of potential prey during the adult stage all tended to be lower in small urban woodlands. These results suggest that decreased reproduction of N. clavata in small urban woodlands is caused by food shortage during the adult stage, particularly a shortage of large insects.

Predator-prey size interaction in tropical ponds

An experiment was set-up to see in mortality inflicted by tadpole predators depends on prey and predator sizes. Fish and dragonfly larvae were used as predators and two size classes of Osteocephalus taurinus tadpoles as prey. Results show that the effect of predators is dependent on the size structure of the prey population. Furthermore, dragonfly larvae are more voracious predators than the fish used in the experiment. Both predators occur in natural ponds where Osteocephalus taurinus lays its eggs. The timing of arrival of predators and prey, which determines the relative sizes of predators and prey, is an important factor determining the outcome of an episode of community interaction in tropical ponds, as in similar temperate systems.

Factors affecting prey selection by young bream Abramis brama and roach Rutilus rutilus: insights provided by parallel studies in laboratory and field

Prey selection by underyearling bream and roach was studied in both the laboratory and field. When presented with cladoceran and a more elusive copepod prey both fish species select against copepods, regardless of the relative prey sizes. However, the field diet of bream, but not roach, consistently includes a large proportion of copepods. The explanation for this discrepancy lies in the timing and location of foraging in the field. Bream foraging, unlike that of roach, is largely restricted to the hours of darkness and to the lowest stratum of the lake. The Microcrustacea of this stratum is depleted of cladocerans at night, because of vertical migration, and is relatively rich in copepods.

Basis of selective predation by the aquatic larvae of the salamander,Ambystoma tigrinum

SUMMARY.1. The effect of several factors on feeding selectivity by three size classes of larvae ofAmbystoma tigrinum(Green) was examined. Five types of invertebrate prey were used:Chaoborus, Daphnia, damselflies,Hyalellaand water boatmen.2. Five variables were examined in relation to the electivity indices associated with each prey type: ease of prey consumption, ease of prey capture, relative prey size, prey activity, and microhabitat overlap. No single variable explained the observed electivity.3. For small larvae (snout‐vent length, SVL, <2.5cm) relative prey size was correlated with electivity. For large larvae (SVL >6.5cm), ease of prey consumption, prey activity, and relative prey size predicted electivity values. However, none of the measured variables was related to electivity values found for medium sized larvae (SVL >3.5 and <5.5cm).

The Shell Size: Prey Size Relationship in Mudsnails

Character displacement resulting from interspecific competition is a central concept in community ecology, yet good examples are few (Arthur 1982). Populations of mudsnails (genus Hydrobia) in the Limfjord, Denmark, provide what has been widely accepted as the most convincing case (Roughgarden 1983). In the Limfjord, H. ulvae and H. ventrosa differ in size when coexisting but are more similar in size when occurring alone (Fenchel 1975b). A broadly similar pattern of shell size variation exists for these species in eastern England (Cherrill and James 1987). However, in a survey of populations around the Jutland coast Hylleberg (1986) failed to find consistent intraspecific differences in shell sizes between allopatric and sympatric populations. Both of these recent studies suggest that shell size may be determined, in large part, by environmental factors. A weakness of all three studies is that the occurrence

Pipefish foraging: effects of fish size, prey size and altered habitat complexity

Laboratory experiments determined the effects of 2 levels of habitat complexity upon pipefish Syngnathus fuscus foraging for amphipods. Habitats were composed of equal densities of either narrow (low complexity) or wide (high complexity) leafed artificial seagrass. Response to habitat as measured by rate of encounter with amphipods, probability of attack after encounter, probability of success after attack, and overall rate of amphipod consumption was determined for combinations of 2 fish size classes and 3 amphlpod size classes. Small fish did not respond to changes in habitat complexity, while large fish &d. Large fish encountered fewer amphipods in the high than in the low complexity habitat. In general encounter rate increased with amphipod size. Large fish attack probability was negatively related to amphipod size in the narrow leaf habitat, but positively related to amphipod size in the wide leaf habitat. Small fish attack probability was negatively related to amphipod size in both habitats. Success was negatively related to prey size and greater for large than for small fish. and showed no overall effect of habitat. The position that amphipods occupy in the structure of vegetation in part determines their vulnerability to predation, a criterion by which pipefish appear to select prey. In this respect pipefish behavior is flexible, allowing adjustment of foraging tactics to match habitat constraints. Results suggest that relative sizes of predator and prey are important factors in determining the effect of structural complexity upon predator-prey dynamics.

Interactions between an Exotic Crayfish and Stocked Rainbow Trout in Newcastle Reservoir, Utah

Crayfish Orconectes virilis appeared in Newcastle Reservoir, Utah, in the 1970s. Rainbow trout Salmo gairdneri are stocked annually in the reservoir to support a sport fishery. Predation of rainbow trout on crayfish was studied during 1983-1985. This predation was seasonal, occurring only during June-December. It was greatest during June-August, when up to 100% of fish stomachs contained crayfish. Relative sizes of predators and prey helped to limit crayfish consumption by fish, but seasonal behavior and distribution of crayfish also influenced their availability. Crayfish of ingestible sizes occupied the reservoir throughout the year, though rainbow trout did not eat them in winter and early spring. Crayfish were consumed up to a size of 38 mm in carapace length (CL). They grew to a size of 22 mm CL during their first year and attained a maximum size of 60 mm CL. Rainbow trout growth declined after crayfish became abundant in 1979. Crayfish changed the reservoir ecosystem by altering the food web and thereby reducing the energy transfer to rainbow trout. Fish-stocking rates were cut in half in 1983 and 1984 to improve the growth rate of rainbow trout.

Prey Size Selection by the Mosquitofish: Relation to Optimal Diet Theory

We investigated size—selective predation upon Daphnia pulex and D. magna by the mosquitofish (Gambusia). The independent variables were the relative size of predator and prey, prey density, and predator satiation. Gambusia actively chose to attack small prey (which we showed to be more profitable). Gambusia's preference increased monotonically, or decreased, or peaked at an intermediate prey size, depending upon fish size, prey size, and fish satiation level. These results contrast with the hypothesis the "gape—limited predators" select the largest prey available, and "size—limited predators" select small or intermediate—sized prey. Optimal diet theory predicts that a predator should drop less profitable prey items from the diet at higher prey densities. In contrast, Gambusia maintained a mixed diet and its preferences did not change in response to changes in either the absolute or the relative abundance of prey. Moreover, the ingestion rate would have been higher if less profitable (larger) prey types had been ignored. Gambusia did sharply alter its size—selective feeding behavior in response to its own satiation level, and we expect that this factor is correlated with prey density in the field. Well—fed fish concentrated their attacks, to a greater degree than starved fish, on small, more profitable prey. They also ingested less biomass per unit time. This last result suggests that maximizing food intake per unit time may not be the goal of well—fed fish, and that different criteria may determine the profitability of prey at different prey densities.

Effects of Cover and Prey Size on Preferences of Juvenile Largemouth Bass for Blue Tilapias and Bluegills in Tanks

Abstract The effects of vegetative cover and relative size of prey were tested on the forage preference of juvenile largemouth bass Micropterus salmoides offered blue tilapias Tilapia aurea and bluegills Lepomis macrochirus in laboratory electivity experiments. When offered forage at or near the maximum consumable size in tanks without vegetative cover, largemouth bass preferred bluegills, but consumed blue tilapias in the presence of vegetation. When offered forage smaller than the maximum consumable size in tanks without vegetation, largemouth bass selected blue tilapias. Differences between the forage species in body morphology and effective use of protective cover apparently caused the changes in prey selection. Our results suggest blue tilapias may be a suitable forage for largemouth bass, but that habitat characteristics and relative size distributions of other available forage may affect their use.

Predator–prey size relationships in North American dabbling ducks

Diets of dabbling ducks (Anas: Anatidae) usually have been recorded only with respect to taxonomic composition and not prey size. Interspecific diet overlap thus has been termed large. However, using published taxonomic diet lists for seven species of ducks, measurements of bill morphology from museum specimens, and "handbook" data on the sizes and caloric density of invertebrates, prey size distributions were found to differ among species (P < 0.001). Also, the sizes of prey in each species' diet differed from that found in the environment. The number of lamellae per centimetre of bill negatively correlated with mean prey size (P < 0.001); body size and bill length did not. Based on the similarity of environmental and dietary prey size distributions, species were classified as specialist or generalist foragers. This classification corresponded well with one generated from analyses of foraging behaviour alone. An explanation for the diminuitive sizes of ducks on islands was advanced: if interspecific competition for food selects for niche divergence among coexisting dabbling ducks along a prey size niche dimension, then in the absence of competition from small species on islands, large solitary species have evolved to a smaller size which may be optimal for the distribution of energy among prey size classes in the environment.

Significance of Sequential Feeding Patterns of Juvenile Rainbow Trout in a Large Lake-Fed River

Abstract Rainbow trout fry Salmo gairdneri, feeding during the day in a large river below a lake, far more frequently attacked drifting organisms than substrate-associated organisms. Recently emerged fry struck at prey more frequently than did older fry. Zooplankton from the lake upstream were the prey most frequently consumed by small fry, whereas larger aquatic and terrestrial insects were the major food of larger fry. Of those zooplankters fed upon by small fry, large calanoid copepods (mainly Epischura nevadensis) and Daphnia galeata mendotae were selectively consumed and smaller Bosmina longirostris rarely consumed, as would be expected of size-selective predators, but large Cyclops bicuspidatus were also under-represented in fry stomachs. There was a seasonal increase in size of prey consumed. The relative prey size (size of prey consumed divided by fry size) increased throughout the year, except from fall to winter when fry growth was slow. It is suggested that the sequential change in feeding patt...

Foraging Tactics of a Terrestrial Salamander: Judging Prey Profitability

(1) Optimal foraging theory predicts that predators will rank all potential types of prey by their profitability and then specialize on the most profitable type when it is abundant. We designed an experiment to test whether the red-backed salamander, Plethodon cinereus (Green), determines the caloric profitability of prey by innate recognition, by relative sizes of the prey or by learning through previous experience with the prey types. (2) Salamanders were trained for 3 months under four conditions: biweekly feedings of (I) both large and small flies, (II) large flies only, (III) small flies only or (IV) a non-dipteran prey. Each group was then given a high density of both large and small flies and choice of diet was determined. (3) Only after Condition I did the salamanders appear to forage 'optimally': expressing a high degree of specialization on large flies, rejecting more encountered small than large flies, pursuing more large than small flies, having shorter intercapture intervals and higher positive rates of net energy. (4) The salamanders did not rely on an inherited ability to assess profitability, because they could specialize on the more profitable prey even though it is not in their natural diet. They did not use relative sizes of prey to judge profitability, because they failed to specialize after Conditions III and IV. (5) We conclude that they learned through foraging experience to assess profitabilities of the prey types. Such experience is necessary to balance off the gross caloric value of the prey types (which can be estimated by size) against the rate at which those prey types can be assimilated once ingested (which is a variable depending on chitinous content of the arthropods).

Foraging Costs and Relative Prey Size

Foraging Costs and Relative Prey Size

Predation by Hydrophilus triangularis and Tropisternus lateralis1 in California Rice Fields

Gut content examinations of the larvae of Hydrophilus triangularis Say and Tropisternus lateralis (F.) (Coleoptera: Hydrophilidae) showed that predation was influenced by the relative size of predator and prey and by the availability of prey. The rice seed midges Cricotopus sylvestris (F.), an undescribed Paratanytarsus sp. (= Tanytarsus sp.), and Paralauterborniella spp. comprised most of the diet, and were apparently selected with greater frequency than their abundance in the rice field community would indicate. The extent of natural control of midges provided by hydrophilid larvae is unknown.

The Feeding Biology of Ant-Lion Larvae: Prey Capture, Handling and Utilization

SUMMARY (1) The general feeding biology of Morter obscurus is described. (2) First instar larvae, because they use a different pit construction technique, have steeper-walled pits than later instars. Pit diameter and larval length are linearly related. (3) Capture success is determined mainly by the relative sizes of predator and prey. For a given relative size instar 1 larvae are more successful because of the steep-walled pits. Capture success drops to zero when ants can place some of their legs outside the pit. Third instar larvae were more successful than second instar larvae in pits of the same size. Capture success, particularly for large larvae, is 100% over much of the prey size range. (4) Successful attacks on ants with thick exoskeletons occurred almost exclusively via the gaster whereas mandible insertion for ants with thin exoskeletons frequently occurred elsewhere. (5) Differences in pit morphology and prey capture behaviour in Macroleon lynceus are documented and related to habitat differences. In Morter, pit morphology is crucial for prey capture, while strength is more important for the larger Macroleon. (6) Handling time was divided into time to capture (Ta), time to death (Td), and time to extract body contents (Te). T, was constant for small prey but increased rapidly for larger prey. Td was constant for all sizes of predator and prey. Te increased with prey size and decreased with increasing predator size and temperature. Te seems to depend not only on the amount of extractable food but also on the shape of the victim. (7) Hunger has no effect on prey handling time or food extraction efficiency. However hungry larvae are more likely to move their pits. Ant-lions can capture prey falling into the pit when already feeding and so increase their food supply. (8) Growth rates of larvae feeding on different sized prey were measured. Large larvae grew more slowly than small ones when fed on the same sized prey because of higher maintenance costs. For a given sized predator, growth per unit weight of prey received declined with increasing prey size because of increased feeding costs. Each size of ant-lion had a prey size for which the costs per unit return were a minimum, this size changing abruptly from very small prey for the first two instars to large prey for the final instar. (9) The feeding biology of the three instars is compared and contrasted. First instar larvae are adapted to achieve a high capture success rate on a small prey size range because feeding costs are high and escapes therefore expensive. For large larvae, maintenance costs are more important and selection has favoured a large size range of catchable prey. While the behaviour of ant-lion larvae is consistent with an energy maximizer strategy it is concluded that the approach is of limited value in this instance.

The association between the sponge Halichondria panicea (Pallas) and scallop Chlamys varia (L.): A commensal-protective mutualism

The scallop Chlamys varia (L.) was found associated with an enveloping epizoitic growth of the sponge Halichondria panicea (Pallas). The bivalve was protected against predatory starfishes by the sponge which interfered with the attachment of tube feet and made the vulnerable byssal opening and valve margins inaccessible to the predator's gastric membranes. Protection was partial or complete depending upon the species of starfish and relative sizes of predator, prey, and epizoite. The effectiveness of the pectinid escape response was enhanced by the sponge which enabled the mollusc to dislodge attacking asteroids. The sponge benefited from an increased supply of suspended nutrients generated by the inhalant current of the host. The partnership is a commensal-protective mutualism of an unspecialized and probably facultative nature. The association has not been reported before although it may have a wide distribution, at least on the Atlantic coast of Ireland.

Predator size and prey size: presumed relationship in the mantid Hierodula coarctata Saussure

Measurements of tibia length and tibial hook angle were used to calculate optimum prey size in 714 specimens of the mantid Hierodula coarctata. These values were then regressed on the cube root of dry body weight to derive a presumed predator–prey size relationship for the species. Energetic arguments are advanced to account for the observed relationship. An interspecific relationship is also demonstrated for three species of mantids and two species of mantis shrimp (stomatopod crustaceans).

The Influence of Hunting Manner on Prey Size, Particularly in Spiders with Long Attack Distances (Araneidae, Linyphiidae, and Salticidae)

Several classifications of foraging manner are related along two axes: the time (from within feeding bouts to among generations) during which locomotion occurs, and the actual level of locomotion. Habitat specialization as "searchers" seems to occur in large species of araneid (orb-web) spider and in small species of salticid (jumping) spider, while small araneid and large salticid species seem to show more specialization for size of prey as "pursuers." The use of larger prey by web than by nonweb spiders is related to the peaked lognormal curve of abundance of insects. Specialization for prey size as a pursuer, then, seems more common in spiders using prey of intermediate sizes, which are most abundant. Specialists for habitat are more usual at the two tails of the insect (prey) abundance curve. The use of nets and poison apparently increases the size of prey used, relative to the predator's size, since web spiders take larger prey than nonweb spiders and the latter take larger prey than chewing insectivores. Nets, poison, surprise, and pack hunting may occur as tools to increase the relative size of prey in both arthropods and vertebrates. Pack hunters seem to be more olfactory, terrestrial, and diurnal in their habits, while hunters which use the other tools are more tactile, arboreal, and nocturnal. A complementary relative species abundance between the Linyphiidae (sheet-web spiders) and Salticidae is discussed in relation to their probable use of similarsized prey. The linyphiids dominate the spider fauna at high latitudes and, in one case at least, replace the salticids among habitats within a latitude, in those habitats with the ground surface disturbed. There may be a relative rarity of small insects in the tropics, or competition with ants may be involved. Analysis of the size, abundance, and motility of insectivores, including insectivorous insects, should predict the relative abundance in particular habitats of species of the various guilds of web and nonweb spider modes, as well as the species, degree of specialization for prey size or for habitat.

The effect of relative prey size on the ingestion behavior of rodent-eating snakes

Six species of snakes from three families that represent diverse phyletic position and prey-capture techniques were fed mice of different sizes. The probability of the prey-capture technique’s being employed and of headfirst ingestion were determined by relative meal size, i.e., ingestion ratio. When dealing with relatively large prey, all constrictors and venomous species reliably located the head prior to ingestion.

Foraging Strategy of a Starfish in Relation to Actual Prey Availability and Environmental Predictability

The foraging ecology of the asteroid Leptasterias hexactis was studied at five rocky intertidal areas in the San Juan Islands, Washington, for 2—2¾ years. Feeding activity during high tides reaches a high point in mid— to late summer (July and August) and a low point in the winter (January). Three probable factors selecting for this cycle are (1) reproduction, virtually immobilizing the females, during the winter; (2) low food availability in winter compared to summer; and (3) violent winter storms. Persistently reduced low tide feeding during all but autumnal night low tides indicates that some light—related factor(s) select for a tidal cycle of feeding also. Factors believed responsible are desiccation stress and possibly predation by visual predators. A graphic model of foraging behavior is presented. Analysis of the diet of Leptasterias by both numbers and calories of prey consumed indicates that this starfish is a food generalist. Moreover, numbers of prey consumed, when compared to prey available, indicate those prey chosen selectively and those which are avoided. Lastly, calories consumed compared to calories available indicate why particular prey are chosen. Many factors are involved in prey choice including ease of capture, relative sizes of predator and prey, and caloric yield of the prey. Actual availability is defined as that portion of available prey (i.e., prey physically present) which could be consumed by a predator. The factors affecting prey choice, coupled with prey and predator distribution, abundance, and behavior must be considered when determining actual availability of prey. Actual availability coefficients are computed and suggest that (1) hard—to—capture prey are least available; (2) Leptasterias is more selective in summer and autumn, when food is more abundant; and (3) prey are more available to large starfish. Calculations suggest that, under normal conditions, Leptasterias would be severely energy—limited in winter if it foraged at rates similar to those of spring or summer, or both. Thus, food limitation may be partially responsible for reduced feeding in winter. Comparison of numerical patterns of consumption of energy—rich and energy—poor prey indicates that energy—rich prey are most important except in summer when energy—poor prey become the most important prey, presumably because of their tremendous numerical increase and domination. Comparisons between the foraging strategy of this starfish and theoretical models previously proposed support some predictions but not others, indicating that complex natural systems require more comprehensive and precise models. Predictability of resources in time and space probably determines the degree of resource specialization or generalization in animals.