RESUMEN
The traditional trophic cascades model is based on consumer resource interactions at each link in a food chain. However, trophic-level interactions, such as mesocarnivore release resulting from intraguild predation, may also be important mediators of cascades. From September 2001 to August 2004, we used spatial and seasonal heterogeneity in wolf distribution and abundance in the southern Greater Yellowstone Ecosystem to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus), accounts for high rates of coyote predation on pronghorn (Antilocapra americana) fawns observed in some areas. Results of this ecological perturbation in wolf densities, coyote densities, and pronghorn neonatal survival at wolf-free and wolf-abundant sites support the existence of a species-level trophic cascade. That wolves precipitated a trophic cascade was evidenced by fawn survival rates that were four-fold higher at sites used by wolves. A negative correlation between coyote and wolf densities supports the hypothesis that interspecific interactions between the two species facilitated the difference in fawn survival. Whereas densities of resident coyotes were similar between wolf-free and wolf-abundant sites, the abundance of transient coyotes was significantly lower in areas used by wolves. Thus, differential effects of wolves on solitary coyotes may be an important mechanism by which wolves limit coyote densities. Our results support the hypothesis that mesopredator release of coyotes contributes to high rates of coyote predation on pronghorn fawns, and demonstrate the importance of alternative food web pathways in structuring the dynamics of terrestrial systems.
Asunto(s)
Antílopes/crecimiento & desarrollo , Conducta Competitiva/fisiología , Coyotes/crecimiento & desarrollo , Ecosistema , Cadena Alimentaria , Conducta Predatoria/fisiología , Lobos/crecimiento & desarrollo , Animales , Femenino , Masculino , Densidad de Población , Dinámica Poblacional , Conducta EspacialRESUMEN
Food web theory predicts that the loss of large carnivores may contribute to elevated predation rates and, hence, declining prey populations, through the process of mesopredator release. However, opportunities to test predictions of the mesopredator release hypothesis are rare, and the extent to which changes in predation rates influence prey population dynamics may not be clear due to a lack of demographic information on the prey population of interest. We utilized spatial and seasonal heterogeneity in wolf distribution and abundance to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus) throughout much of the United States, contributes to high rates of neonatal mortality in ungulates. To test this hypothesis, we contrasted causes of mortality and survival rates of pronghorn (Antilocapra americana) neonates captured at wolf-free and wolf-abundant sites in western Wyoming, USA, between 2002 and 2004. We then used these data to parameterize stochastic population models to heuristically assess the impact of wolves on pronghorn population dynamics due to changes in neonatal survival. Coyote predation was the primary cause of mortality at all sites, but mortality due to coyotes was 34% lower in areas utilized by wolves (P < 0.001). Based on simulation modeling, the realized population growth rate was 0.92 based on fawn survival in the absence of wolves, and 1.06 at sites utilized by wolves. Thus, wolf restoration is predicted to shift the trajectory of the pronghorn population from a declining to an increasing trend. Our results suggest that reintroductions of large carnivores may influence biodiversity through effects on prey populations mediated by mesopredator suppression. In addition, our approach, which combines empirical data on the population of interest with information from other data sources, demonstrates the utility of using simulation modeling to more fully evaluate ecological theories by moving beyond estimating changes in vital rates to analyses of population-level impacts.
Asunto(s)
Antílopes/fisiología , Coyotes/fisiología , Lobos/fisiología , Animales , Productos Biológicos , Conservación de los Recursos Naturales , Ecosistema , Femenino , Masculino , Dinámica Poblacional , WyomingRESUMEN
Interference competition with wolves Canis lupus is hypothesized to limit the distribution and abundance of coyotes Canis latrans, and the extirpation of wolves is often invoked to explain the expansion in coyote range throughout much of North America. We used spatial, seasonal and temporal heterogeneity in wolf distribution and abundance to test the hypothesis that interference competition with wolves limits the distribution and abundance of coyotes. From August 2001 to August 2004, we gathered data on cause-specific mortality and survival rates of coyotes captured at wolf-free and wolf-abundant sites in Grand Teton National Park (GTNP), Wyoming, USA, to determine whether mortality due to wolves is sufficient to reduce coyote densities. We examined whether spatial segregation limits the local distribution of coyotes by evaluating home-range overlap between resident coyotes and wolves, and by contrasting dispersal rates of transient coyotes captured in wolf-free and wolf-abundant areas. Finally, we analysed data on population densities of both species at three study areas across the Greater Yellowstone Ecosystem (GYE) to determine whether an inverse relationship exists between coyote and wolf densities. Although coyotes were the numerically dominant predator, across the GYE, densities varied spatially and temporally in accordance with wolf abundance. Mean coyote densities were 33% lower at wolf-abundant sites in GTNP, and densities declined 39% in Yellowstone National Park following wolf reintroduction. A strong negative relationship between coyote and wolf densities (beta = -3.988, P < 0.005, r(2) = 0.54, n = 16), both within and across study sites, supports the hypothesis that competition with wolves limits coyote populations. Overall mortality of coyotes resulting from wolf predation was low, but wolves were responsible for 56% of transient coyote deaths (n = 5). In addition, dispersal rates of transient coyotes captured at wolf-abundant sites were 117% higher than for transients captured in wolf-free areas. Our results support the hypothesis that coyote abundance is limited by competition with wolves, and suggest that differential effects on survival and dispersal rates of transient coyotes are important mechanisms by which wolves reduce coyote densities.
Asunto(s)
Conducta Competitiva/fisiología , Coyotes/crecimiento & desarrollo , Ecosistema , Conducta Predatoria/fisiología , Lobos/fisiología , Animales , Demografía , Femenino , Masculino , Densidad de Población , Dinámica Poblacional , Estaciones del Año , Conducta Espacial , WyomingRESUMEN
Numerous species undergo impressive movements, but due to massive changes in land use, long distance migration in terrestrial vertebrates has become a highly fragile ecological phenomenon. Uncertainty about the locations of past migrations and the importance of current corridors hampers conservation planning. Using archeological data from historic kill sites and modern methods to track migration, we document an invariant, 150 km (one-way) migration corridor used for at least 6000 years by North America's sole extant endemic ungulate. Pronghorn (Antilocapra americana) from the Greater Yellowstone Ecosystem, like other long distant migrants including Serengeti wildebeest (Connochaetes taurinus) and Arctic caribou (Rangifer tarandus), move nearly 50 km d-1, but in contrast to these other species, rely on an invariant corridor averaging only 2 km wide. Because an entire population accesses a national park (Grand Teton) by passage through bottlenecks as narrow as 121 m, any blockage to movement will result in extirpation. Based on animation of real data coupled with the loss of six historic routes, alternative pathways throughout the 60,000 km2 Yellowstone ecosystem are no longer available. Our findings have implications for developing strategies to protect long distance land migrations in Africa, Asia and North America and to prevent the disappearance of ecological phenomena that have operated for millennia.
Asunto(s)
Migración Animal , Rumiantes/fisiología , Animales , Conservación de los Recursos Naturales , Ecosistema , Femenino , Sistemas de Información Geográfica , Geografía , Factores de Tiempo , WyomingRESUMEN
Despite the importance of carnivores in terrestrial ecosystems, many nations have implemented well-coordinated, state-funded initiatives to remove predators, largely because of conflicts with humans over livestock. Although these control efforts have been successful in terms of the number of carnivores removed, their effects on the viability of the industries they seek to protect are less understood. I assessed the efficacy of long-term efforts by the U.S. government to improve the viability of the sheep industry by reducing predation losses. I used regression analysis and hierarchical partitioning of a 60-year data set to explore associations among changes in sheep numbers and factors such as predator control effort, market prices, and production costs. In addition, I compared trends in the sheep industry in the western United States, where predator control is subsidized and coyotes (Canis latrans) are abundant, with trends in eastern states that lack federally subsidized predator control and that were (1) colonized by coyotes before 1950 or (2) colonized by coyotes between 1950 and 1990. Although control efforts were positively correlated with fluctuations in sheep numbers, production costs and market prices explained most of the model variation, with a combined independent contribution of 77%. Trends in sheep numbers in eastern and western states were highly correlated (r > or = 0.942) independent of the period during which they were colonized by coyotes, indicating either that control has been ineffective at reducing predation losses or that factors other than predation account for the declines in both regions. These results suggest that government-subsidized predator control has failed to prevent the decline in the sheep industry and alternative support mechanisms need to be developed if the goal is to increase sheep production and not simply to kill carnivores.
Asunto(s)
Conservación de los Recursos Naturales/economía , Coyotes/fisiología , Control de Plagas/métodos , Conducta Predatoria/fisiología , Ovinos/fisiología , Crianza de Animales Domésticos/economía , Crianza de Animales Domésticos/tendencias , Animales , Modelos Biológicos , Control de Plagas/economía , Factores de Tiempo , Estados UnidosRESUMEN
We initially evaluated in mice the ability of naked DNA encoding intracellular forms of the E1E2 envelope proteins from HCV to induce antibody responses and compared the responses induced with the same plasmid adsorbed onto cationic poly (lactide co-glycolide) (PLG) microparticles. Although naked DNA was only able to induce detectable responses at the 100 microg dose level, making this approach impractical for evaluation in larger animals, PLG/DNA induced detectable responses at 10 microg. In addition, the PLG/DNA microparticles induced significantly enhanced responses to naked DNA when compared at the same dose level. Remarkably, PLG/DNA induced comparable responses to recombinant E1E2 protein adjuvanted with the emulsion MF59. Furthermore, PLG/DNA effectively primed for a booster response with protein immunization, while naked DNA did not. Therefore, PLG/DNA was selected for further evaluation in a non-human primate model. In a study in rhesus macaques, PLG/DNA induced seroconversion in 3/3 animals following three immunizations. Although the antibody responses appeared lower than those induced with recombinant protein adjuvanted with MF59, following a fourth dose, PLG/DNA and protein induced comparable responses. However, a single booster dose of recombinant protein administered to the animals previously immunized with PLG/DNA induced much higher responses. In addition, one of three animals immunized with PLG/DNA showed a cytotoxic T lymphocyte response in peripheral blood lymphocytes. In conclusion, cationic PLG microparticles with adsorbed HCV DNA generates potent immune responses.
Asunto(s)
Hepatitis C/prevención & control , Ácido Láctico/administración & dosificación , Ácido Poliglicólico/administración & dosificación , Polímeros/administración & dosificación , Vacunas de ADN/administración & dosificación , Vacunas contra Hepatitis Viral/administración & dosificación , Adyuvantes Inmunológicos/administración & dosificación , Adyuvantes Inmunológicos/farmacología , Animales , Cationes , Pruebas Inmunológicas de Citotoxicidad , ADN Viral , Portadores de Fármacos , Sistemas de Liberación de Medicamentos , Anticuerpos contra la Hepatitis C/sangre , Inmunoglobulina G/sangre , Ácido Láctico/química , Ácido Láctico/inmunología , Macaca mulatta , Ratones , Microesferas , Plásmidos/genética , Plásmidos/inmunología , Ácido Poliglicólico/química , Copolímero de Ácido Poliláctico-Ácido Poliglicólico , Polímeros/química , Polisorbatos/administración & dosificación , Polisorbatos/farmacología , Escualeno/administración & dosificación , Escualeno/farmacología , Vacunas de ADN/inmunología , Proteínas del Envoltorio Viral/genética , Proteínas del Envoltorio Viral/inmunología , Vacunas contra Hepatitis Viral/inmunologíaRESUMEN
A diminuiçao da perfusao placentária com conseqüente distúrbio de trocas gasosas ocorre com freqüência após a circulaçao extracorpórea (CEC) fetal experimental. Com o objetivo de caracterizar a hemodinâmica placentária durante a CEC, foram colocadas em CEC sete placentas de ovelhas, isoladas in situ, através da canulaçao dos vasos umbilicais. O fluxo da CEC foi alterado de 15 a 300 ml/min/kg de peso fetal, em normotermia e hipotermia. A resistência vascular placentária (RVP) permaneceu constante durante uma pressao de perfusao e fluxo da CEC acima de 40 mmHg e 150 ml/min/kg, respectivamente. Abaixo destes valores, a relaçao da RVP com estes dois parâmetros foi inversamente proporcional. Um maior aumento da RVP foi observado durante a hipotermia. A implicaçao clínica destes achados reside no fato de que a diminuiçao do fluxo e da pressao de perfusao placentária durante a CEC pode conduzir a um ciclo vicioso, resultando em prejuízo adicional da perfusao placentária das trocas gasosas, sendo que a hipotermia agrava ainda mais esta disfunçao placentária.