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Abstract?Larval western toads (Bufo boreas) are known to exhibit antipredator behavior in response to both chemical alarm cues released from injured conspecifics and chemical cues of predatory invertebrates. In this study, we tested whether long-term exposure to predator and alarm cues resulted in an adaptive shift in life history characteristics of the toads. We raised groups of tadpoles in the presence of: (1) predatory backswimmers (Notonecta spp.) that were fed toad tadpoles, (2) nonpredatory water boatman (Corixidae), and (3) chemical alarm cues of injured conspecifics. Tadpoles raised in the presence of both chemical alarm cues and cues of predators fed tadpoles metamorphosed in significantly shorter time...
Concern over the status of species associated with prairie dog colonies has increased with the recent proposed listing of black-tailed prairie dogs (Cynomys ludovicianus). We monitored burrowing owl (Athene cunicularia) populations and prairie dog densities in 17 black-tailed prairie dog colonies in the Nebraska panhandle between 1990 and 1996. All prairie dog colonies were controlled at least once during the study. We observed a 63% decline in nesting pairs of burrowing owls and significant declines in burrow densities. Results indicated a time lag in owl response to changes in active burrow densities. However, in the later years of the study when burrow densities were lowest, owl numbers were positively correlated...
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Conclusions: Habitat changes resulting from timber harvest have altered the predator–prey balance leading to asymmetric predation affecting the survivial rates of endangered mountain caribou Thresholds/Learnings: As young forest stands increase in proportion to old forests, caribou population densities and survival rates decline as they become increasingly vulnerable to predation and extripation. Synopsis: Timber harvesting in areas of Mountain Caribou habitat have created landscapes of early seral forests. Such habitat changes have altered the predator–prey balance resulting in asymmetric predation in which predators are maintained by alternative prey (i.e. apparent competition). This study estimates survival...
The role of biotic interactions in structuring freshwater invertebrate communities has been extensively studied but with mixed results. For example, fish effects on invertebrates are most pronounced in pelagic and soft-sediment benthic habitats that lack structural complexity, yet appear insignificant in benthic rubble habitats. Backwaters of the Green River, Utah, are shallow, structurally simple, quiet-water embayments adjacent to the river. These habitats form in middle to late summer and are colonized by benthic and epibenthic invertebrates that produce standing crops significantly higher than the river. Backwaters are also utilized by a large number of fish species. We used cages to determine if selective exclusion...
Conclusions:Adult mortality appeared to be largely the result of predation, with cougars accounting for half of the known-cause mortalities. The much higher rate of mortality observed in the more developed portion of the study area supports a link between predation and forestry development.Thresholds/Learnings:
Historically, terrestrial food web theory has been compartmentalized into interactions among aboveground or belowground communities. In this study we took a more synthetic approach to understanding food web interactions by simultaneously examining four trophic levels and investigating how nutrient (nitrogen and carbon) and detrital subsidies impact the ability of the belowground microbial community to alter the abundance of aboveground arthropods (herbivores and predators) associated with the intertidal cord grass Spartina alterniflora. We manipulated carbon, nitrogen, and detrital resources in a field experiment and measured decomposition rate, soil nitrogen pools, plant biomass and quality, herbivore density,...
Nine Heloderma suspectum were observed between 1 April and 13 July 1979. In April and May, movements of Heloderma were associated with areas where eggs of ground nesting birds were most abundant. During June and July, Heloderma responded to decreasing egg availability by shifting their diets to small mammals and moving onto areas where these prey were most abundant. These shifts are adaptive as Heloderma continually exploit the most abundant prey. Lizards demonstrated a foraging strategy of rarely backtracking and consuming only an average of 46% of the eggs available at each nest. The number of eggs eaten per day by each lizard was positively correlated with lizard weight. Combinations of lizard satiation, reproduction,...
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Conclusions: Caribou mortalities attributed to wolf predation were generally closer to a corridor, indicating that linear corridors may enhance wolf predation efficiency. Therefore, caribou existing closer to linear corridors are at a higher risk of depredation than those farther from corridors. Thresholds/Learnings: Synopsis: This study tested the hypothesis that linear corridors affect caribou and wolf activities by examining the distribution of telemetry locations of caribou and wolves, as well as locations of caribou mortality and caribou predation by wolves relative to linear corridors caused by roads, seismic lines, power lines, and pipeline rights-of-way. Caribou mortalities attributed to wolf predation...
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Synopsis: This study examines the influence of landscape fragmentation on trophic cascades in southern California. Results indicate that, as habitat fragmentation negatively affects the persistence of coyote populations, the abundance of smaller meso-predators increase, resulting in higher mortality rates in scrub-breeding birds. Fragment size was a strong indicator of coyote abundance, and coyote abundance was a strong indicator of bird diversity, as coyotes kept down the number of meso-predators that prey on birds. The positive effect of fragment area and the negative effect of fragment age were the strongest determinants of bird diversity in this system. Conclusions: Fragment size correlates with coyote abundance,...
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Conclusions: Nest predators with different home-range sizes and habitat affinities responded to landscape configuration in different ways. Influence of landscape structure varied across scale. Thresholds/Learnings: Herbaceous cover was negatively associated with predation in roadsides whereas the proximity of woody cover was positively associated with predation rates. Synopsis: This study evaluated the influence of habitat structure and spatial configuration on nest predation in central Iowa. In a multi-scale analysis of 10 artificial ground nests along 136 roadsides across six watersheds, researchers found that predation was affected by the surrounding landscape mosaic. Nest predators with different home-range...
This study demonstratest he correlationo f an arrayo f ecological characteristicsw ith foraging mode in sit-and-wait foraging Crotalus cerastes and widely foraging Masticophis flagellum. Crotalus cerastes are chiefly nocturnal and spend most of their time on the surface either coiled on or partially buried in the sand waiting to ambush prey. Masticophis flagellum are strictly diurnal predators and cruise through the habitat searching for active and sedentary prey. In this study, C. cerastes averaged 7.2 ? 0.7 (SE) h/day on the surface, almost twice the time of M. flagellum (3.9 ? 0.9 h/day). Body temperatures (Tb's) of active M. flagellum, determined from surgically implanted radio transmitters, were significantly...
The desert tortoise Gopherus agassizii is federally listed as Threatened because of documented declines in some populations, yet the proximate causes of these declines are not well understood. With use of radiotelemetry, I monitored a total of 55 individual tortoises at two Mojave Desert sites over three years. Both populations suffered high adult mortality during an extreme drought period, but the temporal pattern and inferred proximate causes of mortality differed between sites. At the eastern Mojave site, no telemetered tortoises died in 1988 or 1989, but 41% died in 1990. All nine carcasses were found and only one showed any evidence of predation or scavenging. Tortoises that died had symptoms of dehydration...
Understanding how communities respond to changes in temperature is a major challenge for community ecology. Temperature influences the relative degree to which top-down and bottom-up forces structure ecological communities. In greenhouse experiments using the aquatic community found in pitcher plants (Sarracenia purpurea), I tested how temperature affected the relative importance of top-down (mosquito predation) and bottom-up (ant carcasses) forces on protozoa and bacteria populations. While bottom-up effects did not vary consistently with temperature, the top-down effects of predators on protozoa increased at higher temperatures. These results suggest that temperature could change the relative importance of top-down...
    map background search result map search result map Distribution of caribou and wolves in relation to linear corridors Changes in landscape composition influence the decline of a threatened woodland caribou population Effects of landscape structure on nest predation on roadsides of a mid-western agroecosystem: a multi-scale analysis. Mesopredator release and avifaunal extinctions in a fragmented system. Distribution of caribou and wolves in relation to linear corridors Effects of landscape structure on nest predation on roadsides of a mid-western agroecosystem: a multi-scale analysis. Changes in landscape composition influence the decline of a threatened woodland caribou population Mesopredator release and avifaunal extinctions in a fragmented system.