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  • Foraging  (55)
  • 1
    ISSN: 1432-1939
    Keywords: Key words Pinnipeds ; Foraging ; Migration ; Stable isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We investigated the impact of foraging location (nearshore vs offshore) and foraging latitude (high vs middle) on the carbon (δ13C) and nitrogen (δ15N) isotope compositions of bone collagen of northern fur seals (Callorhinus ursinus), harbor seals (Phoca vitulina), California sea lions (Zalophus californianus), and northern elephant seals (Mirounga angustirostris). Nearshore-foraging harbor seals from California had δ13C values 2.0‰ higher than female northern elephant seals foraging offshore at similar latitudes. Likewise, nearshore-foraging harbor seals from Alaska had values 1.7‰ higher than male northern fur seals, which forage offshore at high latitudes. Middle-latitude pinnipeds foraging in either the nearshore or offshore were 13C enriched by ∼1.0‰ over similar populations from high latitudes. Male northern elephant seals migrate between middle and high latitudes, but they had δ13C values similar to high-latitude, nearshore foragers. Female northern fur seal δ13C values were intermediate between those of high- and middle-latitude offshore foragers, reflecting their migration between high- and middle-latitude waters. The δ13C values of California sea lions were intermediate between nearshore- and offshore-foraging pinnipeds at middle latitudes, yet there was no observational support for the suggestion that they use offshore food webs. We suggest that their “intermediate” values reflect migration between highly productive and less-productive, nearshore ecosystems on the Pacific coasts of California and Mexico. The relative uniformity among all of these pinnipeds in δ15N values, which are strongly sensitive to trophic level, reveals that the carbon isotope patterns result from differences in the δ13C of organic carbon at the base of the food web, rather than differences in trophic structure, among these regions. Finally, the magnitude and direction of the observed nearshore-offshore and high-to middle-latitude differences in δ13C values suggest that these gradients may chiefly reflect differences in rates and magnitudes of phytoplankton production as well as the δ13C value of inorganic carbon available for photosynthesis, rather than the input of 13C-enriched macroalgal carbon to nearshore food webs.
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  • 2
    ISSN: 1432-1939
    Keywords: Key words Microhabitat choice ; Foraging ; Safety ; Predation risk ; Life history
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  In Idotea baltica, a marine isopod that lives and feeds on the brown alga Fucus vesiculosus, microhabitat choice differs between sexes so that males are found more often than females on the light-coloured and exposed apical parts of the alga. We investigated how the requirements of avoiding visual predators and feeding were related to microhabitat choice in relation to diurnal and life-cycle stage in males and females. Faced with a choice between an apical and a basal piece of the alga, females spent more time than males on the basal piece, but this difference was not due to food choice. Faced with a choice between a dark, concealing and a light, exposing background, the preference for a dark background was stronger at day than at night, and stronger in females than in males. This suggests that a sex difference in the importance of avoiding visual predators can explain the sex difference in microhabitat choice. Further, the preference for a dark background and night feeding both increased with age, suggesting that feeding is increasingly subordinated to the need to avoid visual predators. Our experiment found no effect of the presence of the opposite sex on microhabitat choice. Our results support the hypothesis that the sexes trade off feeding against predation risk differently, presumably because growth is more important to males than to females, which have more to gain by protection and therefore spend more time on the lower parts of the alga.
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  • 3
    ISSN: 1432-1939
    Keywords: Intercropping ; Phyllotreta ; Experimental design ; Cropping patterns ; Patch choice ; Foraging ; Foraging movement ; Agroecosystems ; Insect-plant interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Does the response of insect herbivores to the spatial dispersion of their food plants depend on whether alternative dispersions are available? To answer this question, four quartets of collard plots (Brassicae oleracae) were planted. Quartets contained two pairs of plots representing alternative planting designs. In one pair the alternatives were separated from one and other by a curtain barrier that effectively prevented plot to plot movement by the flea beetle, Phyllotreta cruciferae. The boundary between the other pair of alternatives was without barriers, and the beetles could range freely between these two plots. We hypothesized that the presence of a choice (i.e. the absence of a barrier) would exaggerate any differences in beetle numbers between the alternative plant arrangements. Beetles were given “choices” between two kinds of alternatives. In two quartets, the alternatives were high density collard monocultures versus low density collard monocultures. In the other two quartets, the alternatives were collard monocultures versus collard-potato discultures. In each quartet, the abundances of P. cruciferae were censused weekly for three weeks. As we hypothesized, the influence of cropping pattern (both diversity and density) was less where there was a barrier between cropping alternatives than where there was no barrier between the same alternatives. This suggests that nonrandom foraging movement, or “patch choice”, explains the response of Phyllotreta to cropping treatments. The consequence of this mechanism for interpreting the results of insect-host experiments are substantial; experimental designs allowing insects to move and accumulate in a preferred treatment may have different results from the same treatments in isolation.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 72 (1987), S. 473-478 
    ISSN: 1432-1939
    Keywords: Foraging ; Hunger ; Plecoptera ; Profitability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The influences of hunger and prey size on prey selection by the stonefly Hesperoperla pacifica (Perlidae) were explored in the laboratory by observing behavioral responses toward ten prey taxa and three nonprey taxa. Patterns of behavior were consistent with most assumptions and predictions of optimal foraging theory predicting sizebased prey selection by pursuing predators. Handling time appeared to increase as an exponential function of prey mass, and prey profitability (mg/s) was highest for small and intermediate-sized prey. Fasted stoneflies consumed a wide range of prey sizes, whereas well-fed stoneflies concentrated their attacks on intermediate-sized prey. Responses of H. pacifica to nonprey taxa, however, suggest that prey recognition and selection are not based on size alone.
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  • 5
    ISSN: 1432-1939
    Keywords: Clonal growth ; Clonal integration ; Foraging ; Glechoma hederacea ; Translocation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The costs and benefits, measured in terms of dry weight, of physiological integration between clonal ramets, were analysed in two experiments conducted on the clonal herb Glechoma hederacea. Firstly, integration between consecutively-produced ramets was examined in an experiment in which stolons grew from one set of growing conditions (either unshaded or shaded and either nutrient-rich or nutrient-poor) into conditions in which light or nutrient level was altered. Comparisons were made between the dry weight of the parts of the clones produced before and after growing conditions were changed, and the dry weights of the corresponding part of control clones subjected to constant growing conditions. In a second experiment, integration between two distinct parts of G. hederacea clones was investigated. In this experiment clones were grown from two connected parent ramets and the parts of the clone produced by each parent ramet were subjected independently to either nutrient-rich or nutrient-poor conditions. Ramets in resource-rich conditions provided considerable physiological support to those in resource-poor conditions. This was measured as a dry weight gain compared with the weight of the corresponding part of the control clones growing in resource-poor conditions. However, when stolons grew from resource-poor conditions into resource-rich conditions, there was no similar evidence of the resourcepoor ramtes receiving support from resource-rich ramets. Physiological integration did not result in dry weight gains when this would have necessitated basipetal translocation of resources.Because of the predominantly acropedal direction of movement of translocates in G. hederacea, the structure of the clone was important in determining the effectiveness of integration between ramets. Where physiological integration was effective, the cost to the supporting ramets in terms of dry weight was insignificant. Physiological integration allows clones to maintain a presence in less favourable sites with insignificant cost to ramets in favourable sites, thereby reducing the probability of invasion by other plants, and providing the potential for rapid clonal growth if conditions improve. Integrated support of ramets in unfavourable conditions also enables the clone to grow through unfavourable sites, thus increasing the probability of encountering more favourable conditions by wider foraging.
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  • 6
    ISSN: 1432-1939
    Keywords: Canada Goose ; Digestion ; Foraging ; Grazing ; Tundra
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Time spent foraging (and in other activities), rate of pecking at food items and length of foraging and nonforaging periods were studied in cackling Canada goose (Branta canadensis minima) goslings during brood-rearing on the Yukon-Kuskokwim Delta, Alaska in 1978 and 1979. Brood density on the study area was twice as high in 1978 (23 broods) as in 1979 (12 broods) owing in part to annual variation in nesting density and success. Peck-rates were lower in meadows during 1978 than in 1979. There was no between-year difference in time spent foraging prior to the adult molt (59% of daylight hours) but during molt, goslings spent more time feeding in 1978 (70%) than in 1979 (56%). Prior to the adult molt, 12.2 and 11.9 hours were spent feeding each day in 1978 and 1979 respectively, whereas goslings fed for 13.4 and 10.6 hours daily, in the two years during molting and fledging. Increased foraging time during the molt in 1978 completely compensated for lower peck rates so that total number of pecks per day during this period were similar in 1978 (62,800 pecks/d) and 1979 (57,900 pecks/d). Elsewhere, we reported that cackling geese significantly reduced the availability of their preferred food in 1979 and this food comprised a smaller proportion of the diet in 1978 than 1979. This variation in diet suggests that preferred foods were less available at higher brood densities, resulting in annual variation in foraging behavior. Lengths of foraging periods increased during brood-rearing in both years but were longer on average in 1978. There was no seasonal or between year variation in the length of nonforaging periods. The alternating pattern of foraging and nonforaging periods suggests that rate of processing limits rate of food intake because a relatively constant period of time was regularly required to empty the esophagus before foraging could be resumed. The restriction of food intake by digestive processes increased the importance of dietary nutrient concentrations because low nutrient concentrations could not be compensated for by higher rates of food intake.
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  • 7
    ISSN: 1432-1939
    Keywords: Atta cephalotes ; Foraging ; Costa Rica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A month-long study was conducted on the comparative foraging behavior of 20 colonies of the leafcutting ant, Atta cephalotes L. in Santa Rosa National Park, Guanacaste Province, Costa Rica. The study was conducted during the middle of the wet season, when trees had mature foliage and the ants were maximally selective among species of potential host plants. The colonies always gathered leaves from more than a single tree species but on average one species constituted almost half the diet with the remaining species being of geometrically decreasing importance. Colonies exhibited greater diversity in their choice of leaves and lower constancy of foraging when the average quality of resource trees was lower, as predicted by elementary optimal foraging theory. Furthermore, the ants were more selective of the species they attacked at greater distances from the nest. However, the ants sometimes did not attack apparently palatable species, and often did not attack nearby individuals of species they were exploiting at greater distances. A classical explanation for why leafcutting ants exploit distant host trees when apparently equally good trees are nearer, is that the ants are pursuing a strategy of conserving resources to avoid long-term overgrazing pressure on nearby trees. We prefer a simpler hypothesis: (1) Trees of exploited species exhibit individual variation in the acceptability of their leaves to the ants. (2) The abundance of a species will generally increase with area and radial distance from the nest, so the probability that at least one tree of the species will be acceptable to the ants also increases with distance. (3) The ants forage using a system of trunk-trails cleared of leaf litter, which significantly reduces their travel time to previously discovered, high-quality resource trees (by a factor of 4- to 10-fold). (4) Foragers are unware of the total pool of resources available to the colony. Therefore once scouts have chanced upon a tree which is acceptable, the colony will concentrate on harvesting from that tree rather than searching for additional sources of leaves distant from the established trail.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 74 (1988), S. 546-550 
    ISSN: 1432-1939
    Keywords: Energetics ; Albatross ; Incubation ; Foraging ; Seabirds
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The energy expenditure of incubating and foraging Laysan Albatross (Diomedea immutabilis, mean body weight 3.07 kg) was estimated by means of the doubly-labelled water technique. During incubation, the energy expenditure was similar to that of resting birds that were not incubating an egg. The energy expenditure of foraging albatross (2072 kJ/day) was 2.6 times that of resting birds. It was concluded that the energy expenditure of the tropical Laysan Albatross was not less than that of species foraging over cold, high-latitude oceans. An energy budget compiled for an incubating pair of albatross revealed that the energy expenditure of the female was greater than that of the male bird, during the incubation period.
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  • 9
    ISSN: 1432-1939
    Keywords: Ornithoptera ; Amegilla ; Territoriality ; Foraging ; Thermoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The foraging activities of the papilionid butterflies Ornithoptera priamus poseidon and Papilio ulysses, and the solitary bee Amegilla sapiens (Apoidea, Anthophoridae) on the shrub Stachytarpheta mutabilis were studied in highland Papua New Guinea. 2. The insects' activity patterns were analysed at three sites with differing diurnal microclimate variation. O. priamus and A. sapiens foraged in the morning (after a period of basking and wing-whirring) and late afternoon when temperatures were well below daily maxima, whereas P. ulysses showed foraging peaks during the hottest part of the day. 3. Site choice by all 3 species appeared to be determined primarily by temperature, but within the limits imposed by temperature, nectar supplies probably determined which site was visited. 4. P. ulysses showed interspersed foraging and courtship behaviour, and no behavioural switching was observed for this species. At high temperatures, both O. priamus and A. sapiens ceased foraging and showed territorial and courtship behaviour. This behavioural change allowed avoidance of heat stress, and occurred even when nectar supplies were maintained at high levels. 5. Thermal effects on behavioural switching in these insects are compared with related phenomena in other bees and butterflies.
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  • 10
    ISSN: 1432-1939
    Keywords: Foraging ; Rules of thumb ; Spider ; Stochastic model ; Yield profile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We compared the patch-choice performances of an ambush predator, the crab spider Misumena vatia (Thomisidae) hunting on common milkweed Asclepias syriaca (Asclepiadaceae) umbles, with two stochastic rule-of-thumb simulation models: one that employed a threshold giving-up time and one that assumed a fixed probability of moving. Adult female Misumena were placed on milkweed plants with three umbels, each with markedly different numbers of flower-seeking prey. Using a variety of visitation regimes derived from observed visitation patterns of insect prey, we found that decreases in among-umbel variance in visitation rates or increases in overall mean visitation rates reduced the “clarity of the optimum” (the difference in the yield obtained as foraging behavior changes), both locally and globally. Yield profiles from both models were extremely flat or jagged over a wide range of prey visitation regimes; thus, differences between optimal and “next-best” strategies differed only modestly over large parts of the “foraging landscape”. Although optimal yields from fixed probability simulations were one-third to one-half those obtained from threshold simulations, spiders appear to depart umbels in accordance with the fixed probability rule.
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