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Richard Shine - One of the best experts on this subject based on the ideXlab platform.
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the early toad gets the worm cane toads at an invasion front benefit from higher Prey Availability
Journal of Animal Ecology, 2013Co-Authors: Gregory P Brown, Crystal Kelehear, Richard ShineAbstract:Summary In biological invasions, rates of range expansion tend to accelerate through time. What kind of benefits to more rapidly dispersing organisms might impose natural selection for faster rates of dispersal, and hence the evolution of range-edge acceleration? We can answer that question by comparing fitness-relevant ecological traits of individuals at the invasion front compared with conspecifics in the same area a few years post-invasion. In tropical Australia, the rate of invasion by cane toads (Rhinella marina) has increased substantially over recent decades, due to shifts in heritable traits. Our data on field-collected cane toads at a recently invaded site in the Australian wet–dry tropics span a 5-year period beginning with toad arrival. Compared with conspecifics that we monitored in the same sites post-invasion, toads in the invasion vanguard exhibited higher feeding rates, larger energy stores, better body condition and faster growth. Three processes may have contributed to this pattern: (i) higher Prey Availability at the front (perhaps due to reduced competition from conspecifics); (ii) the lack of viability-reducing parasites and pathogens in invasion-front toads; and (iii) distinctive (active, fast-growing) phenotypes of the invasion-front toads. Nutritional benefits to individuals in the invasion vanguard (whether because of higher Prey Availability, or lower pathogen levels) thus may have conferred a selective advantage to accelerated dispersal in this system.
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silver spoons and snake body sizes Prey Availability early in life influences long term growth rates of free ranging pythons
Journal of Animal Ecology, 2000Co-Authors: Thomas Madsen, Richard ShineAbstract:Summary 1. A 13-year study of free-ranging water pythons (Liasis fuscus) and their main Prey (dusky rats, Rattus colletti) in tropical Australia provided extensive data on the relationship between python growth rates and Prey Availability. 2. Python growth rates exhibited considerable variation among individuals. Growth rates of siblings were not correlated, suggesting that environmental rather than genetic factors cause this wide variation. 3. The Availability of Prey varied considerably among years, due to annual variation in rainfall patterns. Pythons grew more rapidly in years with high rat abundance than in years when rats were scarce. Also, python cohorts that hatched in years when Prey were abundant exhibited faster growth rates than those that hatched when Prey were scarce. 4. The snakes showed strong ontogenetic consistency in relative growth rates: that is, an individual with faster-than-average growth in its first year of life continued to grow rapidly throughout the study period. Thus, these pythons displayed a strong ‘silver spoon’ effect, whereby favourable conditions (high Prey abundance) in the first year of life exerted a long-term effect on growth trajectories and thus, adult body sizes. This effect was strongest in the faster-growing sex (females). 5. Hence, the current body size composition of the python population reflects stochastic rainfall-induced annual variation in Prey Availability over the preceding decades.
Dale E. Gawlik - One of the best experts on this subject based on the ideXlab platform.
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physiological condition of juvenile wading birds in relation to multiple landscape stressors in the florida everglades effects of hydrology Prey Availability and mercury bioaccumulation
PLOS ONE, 2014Co-Authors: Garth Herring, Dale E. Gawlik, Collin A Eaglessmith, James M Beerens, Joshua T AckermanAbstract:The physiological condition of juvenile birds can be influenced by multiple ecological stressors, and few studies have concurrently considered the effects of environmental contaminants in combination with ecological attributes that can influence foraging conditions and Prey Availability. Using three temporally distinct indices of physiological condition, we compared the physiological response of nestling great egrets (Ardea alba) and white ibises (Eudocimus albus) to changing Prey Availability, hydrology (water depth, recession rate), and mercury exposure in the Florida Everglades. We found that the physiological response of chicks varied between species and among environmental variables. Chick body condition (shortterm index) and fecal corticosterone levels (medium-term) were influenced by wetland water depth, Prey Availability, region, and age, but not by mercury contamination. However, mercury exposure did influence heat shock protein 70 (HSP70) in egret chicks, indicating a longer-term physiological response to contamination. Our results indicate that the physiological condition of egret and ibis chicks were influenced by several environmental stressors, and the time frame of the effect may depend on the specialized foraging behavior of the adults provisioning the chicks.
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Differential physiological responses to Prey Availability by the great egret and white Ibis
Journal of Wildlife Management, 2012Co-Authors: Garth Herring, Dale E. GawlikAbstract:In long-lived species, the balance between the benefits of reproduction and the costs from reduced survival or productivity is particularly challenging in dynamic environments like wetlands, where food levels vary greatly year to year. Some wetland species exhibit changes in reproductive strategies in response to food Availability but whether physiological responses function in a similar manner is unclear. We compared the pre-breeding physiological responses (fecal corticosterone [FCORT], heat shock protein 60 [HSP60], and mass) of 2 species of wading birds with contrasting foraging strategies (great egret [Ardea alba], an exploiter, and white ibis [Eudocimus albus], a searcher) during years with contrasting levels of Prey Availability. Both species were in good physiological condition, with low levels of HSP60 and FCORT, during a year with high Prey Availability (2006). In a contrasting year with lesser Prey Availability (2007), HSP60 and FCORT concentrations indicated that ibis physiological condition was reduced, whereas egrets showed little change. Egrets and male ibis increased body mass, whereas female ibis decreased mass, in the year with low Prey Availability. Although poorly understood, we hypothesize that the differential response between female ibis and the others is associated with differential investment strategies based on long-term costs of reproduction. Model results identified Prey Availability and the 2-week water recession rate as the primary habitat variables that were associated with the physiological condition of white ibises, whereas great egret physiological condition was influenced mostly by 2-week water recession rate. Our results support the hypothesis that Prey Availability and hydrological factors play crucial roles in regulating populations of wading birds in the Florida Everglades. The results of this study show a more complete pathway by which hydrologic patterns affect wading birds, and it suggests that ibis are more sensitive to habitat conditions than are egrets. This information can be used to refine species models designed to evaluate water management scenarios and will improve our ability to manage and restore wetland ecosystems © 2012 The Wildlife Society.
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sensitivity of nesting great egrets ardea alba and white ibises eudocimus albus to reduced Prey Availability
The Auk, 2010Co-Authors: Garth Herring, Dale E. Gawlik, James M Beerens, Mark I CookAbstract:ABSTRACT. Life-history theory suggests that long-lived bird species will adjust their nesting effort according to current conditions to balance the costs and benefits of current reproduction with their long-term needs for survival and future reproduction. However, responses to the same habitat conditions may differ between species, even within the same ecosystem, to produce different nesting and population patterns. We examined differences in the nesting ecology of two sympatric wading species, Great Egret (Ardea alba) and White Ibis (Eudocimus albus), between years with high (2006) and below-average (2007) Prey Availability in the Florida Everglades. Clutch size of White Ibises decreased by ∼19% from 2006 to 2007, whereas Great Egret clutch size remained constant. Model selection identified rain, water depth, Julian date, year, and Prey biomass as parameters that most influenced daily survival rates (DSR) of White Ibis nests, whereas nest stage, region, Julian date, water depth, and the quadratic form of...
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the effects of Prey Availability on the numerical response of wading birds
Ecological Monographs, 2002Co-Authors: Dale E. GawlikAbstract:Reduced Prey Availability has emerged as a primary hypothesis to explain population constraints on wading birds in numerous wetlands around the world. However, there is almost no understanding of which component of Prey Availability (i.e., Prey density or vulnerability of Prey to capture) is affecting populations and whether the relative effects of each component differ among species. In this study, I manipulated Prey density and water depth (i.e., Prey Availability) in 12 0.2-ha ponds to determine their relative effects on the numeric response of eight species of free-ranging wading birds (White Ibis, Eudocimus albus; Wood Stork, Mycteria americana; Snowy Egret, Egretta thula; Glossy Ibis, Plegadis falcinellus; Great Egret, Ardea alba; Tricolored Heron, Egretta tricolor; Great Blue Heron, Ardea herodias; and Little Blue Heron, Egretta caerulea). The experiment was conducted in a constructed wetland adjacent to, and west of, the northern tip of the remnant Everglades, in Palm Beach County, Florida, USA. Each pond was set to a water depth of 10 cm, 19 cm, or 28 cm, and was stocked with golden shiners (Notemigonus crysoleucas) at a density of either 3 fish/m2 or 10 fish/m2. Total bird use (all treatments pooled) increased from day 1 (day after stocking) to day 6, stabilized for several days at ∼280 birds, and then decreased until day 16, when bird use nearly ceased. Fish were depleted most rapidly in the shallow treatment and least rapidly in the deep treatment. The giving-up-density (GUD) of Prey increased with increasing water depth. There was no significant difference among species in the slope of that relationship; however, a visual inspection of the data showed that differences in GUDs were becoming more apparent in the deepest treatment. At that depth, the White Ibis, Wood Stork, and Snowy Egret had higher GUDs than did the Glossy Ibis, Great Egret, Tricolored Heron, Great Blue Heron, and Little Blue Heron. Also, the first three species were affected significantly by both Prey density and water depth, whereas the latter five species showed a decidedly weaker response to one or the other component of Prey Availability. The first three species were more abundant in the shallow treatments and the high Prey density treatments, and they abandoned the study site before other species reached their maximum density. The feeding strategy of the first group appeared to be one of searching for new high-quality food patches rather than staying and exploiting food patches that were declining in quality. Species that employed a searching strategy also have shown the most severe population declines, suggesting that factors affecting bird density at feeding sites may also have affected population size.
John R H Hoxmeier - One of the best experts on this subject based on the ideXlab platform.
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growth and survival of age 0 walleye sander vitreus interactions among walleye size Prey Availability predation and abiotic factors
Canadian Journal of Fisheries and Aquatic Sciences, 2006Co-Authors: John R H Hoxmeier, David H Wahl, Ronald C Brooks, Roy C HeidingerAbstract:We examined the importance of Prey Availability, predation, and abiotic factors in determining growth and survival of age-0 walleye (Sander vitreus) across 15 Illinois reservoirs during 7 years. Multiple life stages were examined by stocking walleye at three different size groups: larval (6 mm total length (TL)), small (46 mm TL), and large (100 mm TL). Factors affecting growth and survival of walleye varied depending on walleye size. Growth of small and large walleye increased with benthic invertebrate density. Temperature had a positive effect on larval and small walleye growth but a negative effect on large walleye growth. Prey Availability was an important factor for walleye survival across all size groups, whereas temperature affected only larval and large walleye. Juvenile centrarchid density had a negative effect on larval walleye survival, presumably caused by predation. Our best predictive models explained substantial variation in survival for larval (97%), small (57%), and large (83%) walleye. W...
Yael Lubin - One of the best experts on this subject based on the ideXlab platform.
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EFFECTS OF CLIMATE AND Prey Availability ON FORAGING IN A SOCIAL SPIDER, STEGODYPHUS MIMOSARUM (ARANEAE, ERESIDAE)
Journal of Arachnology, 2000Co-Authors: Tanza Crouch, Yael LubinAbstract:Abstract Tropical areas with favorable climatic conditions, high Prey Availability and large Prey size are assumed to favor sociality in spiders. Notwithstanding, the three social species of Stegodyphus (Eresidae) inhabit arid and semi-arid habitats with marked daily and seasonal variation in climate. The nests of the social spider Stegodyphus mimosarum Pavesi commonly occur in dry Acacia savanna in southern Africa. We investigated the abiotic conditions to which the nests of S. mimosarum are exposed and the changes in Availability of potential insect Prey at different times of year and over the daily cycle. We used these data to determine the extent to which Prey Availability and climatic conditions explain seasonal and daily variation in the activity of the spiders. Data were collected during four sampling periods a year over two years from nests of S. mimosarum located on the Mkomazi River Bridge (KwaZulu-Natal, South Africa). We measured ambient and nest temperatures and in a sample of nests, spider g...
James D. Harwood - One of the best experts on this subject based on the ideXlab platform.
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Selectivity underlies the dissociation between seasonal Prey Availability and Prey consumption in a generalist predator
Molecular Ecology, 2018Co-Authors: Thomas D. Whitney, Michael I. Sitvarin, Edward A. Roualdes, Simon J. Bonner, James D. HarwoodAbstract:: Generalist predators are capable of selective foraging, but are predicted to feed in close proportion to Prey Availability to maximize energetic intake especially when overall Prey Availability is low. By extension, they are also expected to feed in a more frequency-dependent manner during winter compared to the more favourable foraging conditions during spring, summer and fall seasons. For 18 months, we observed the foraging patterns of forest-dwelling wolf spiders from the genus Schizocosa (Araneae: Lycosidae) using PCR-based gut-content analysis and simultaneously monitored the activity densities of two common Prey: springtails (Collembola) and flies (Diptera). Rates of Prey detection within spider guts relative to rates of Prey collected in traps were estimated using Roualdes' cst model and compared using various linear contrasts to make inferences pertaining to seasonal Prey selectivity. Results indicated spiders foraged selectively over the course of the study, contrary to predictions derived from optimal foraging theory. Even during winter, with overall low Prey densities, the relative rates of predation compared to available Prey differed significantly over time and by Prey group. Moreover, these spiders appeared to diversify their diets; the least abundant Prey group was consistently overrepresented in the diet within a given season. We suggest that foraging in generalist predators is not necessarily restricted to frequency dependency during winter. In fact, foraging motives other than energy maximization, such as a more nutrient-focused strategy, may also be optimal for generalist predators during Prey-scarce winters.
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Influence of Prey Availability on seasonal fluctuation in body condition in the wolf spider, Pardosa milvina (Araneae: Lycosidae)
Journal of Arachnology, 2013Co-Authors: Jason M. Schmidt, James D. Harwood, Ann L. RypstraAbstract:Abstract Foraging by an organism varies over the season in response to environmental conditions. Predatory arthropods, such as spiders, are frequently in a food-limited state despite their polyphagous habits and may feed opportunistically to enhance rates of growth, survival and reproduction. We predicted that, to circumvent food limitation, spider foraging would be related to Prey Availability. We examined the extent to which body condition of spiders, a correlate of recent foraging, was related to Prey Availability and habitat type. Wolf spiders Pardosa milvina (Hentz 1844) were collected between May and October in two habitat types, corn and soybean fields. To assess changes in spider condition, we calculated and compared multiple body condition indices derived from morphometric measures of individual spiders. Prey abundance was monitored over the same period using a vacuum suction sampler. Body condition indices provided qualitatively equivalent results. Interestingly, juvenile males were in better co...
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living where the food is web location by linyphiid spiders in relation to Prey Availability in winter wheat
Journal of Applied Ecology, 2001Co-Authors: James D. Harwood, K D Sunderland, William Oliver Christian SymondsonAbstract:Summary 1. Spiders form a major component of the generalist predator fauna, potentially able to restrict pest population growth, but their populations may be food-limited under current farming regimes. This study aimed to quantify food Availability to spiders in winter wheat and to determine whether spider web locations are positively associated with available food resources. 2. Mini-sticky traps (Availability rate per 24 h, including Prey falling from the crop) and mini-quadrats (instantaneous density on the ground by day) were used, in combination, to monitor the Availability of potential Prey to web-building species of money spider (Linyphiidae) in fields of winter wheat in Warwickshire, UK, 1997‐98. 3. These methods were applied to web sites of individual spiders and to non-web sites located randomly up to 30 cm away from each web. A total of 18 546 invertebrates were captured using these methods. 4. Overall, significantly more potential Prey were available in web sites than in non-web sites (both on sticky traps and in quadrats). 5. Prey Availability in May and July was about a third of that in June (both on sticky traps and in quadrats) and may have been below that known to be necessary for spiders to realize their maximum population growth rate. 6. The peak rate of capture of linyphiid spiders on mini-sticky traps was 0·6 trap ‐1 day ‐1 at web sites, and approximately half this value at non-web sites. Numbers of spiders captured by mini-sticky traps and mini-quadrats increased exponentially as the season progressed. The high capture frequency in relation to population density, and the differential between web and non-web sites, points to a dynamic and aggregated distribution of spiders in winter wheat, which is consistent with what is known about mate-searching and web site abandonment rates by the Linyphiidae. 7. The combination of techniques described here is recommended for monitoring Prey Availability in Prey-enhancement programmes and may prove useful in quantitative studies of both intra- and interspecific interactions between spiders.