51 research outputs found
Feral Goats and Sheep
Sheep and goats are among the earliest animals domesticated by mankind (Zeder 2009). Both goats and sheep may have made better candidates for domestication than other animals like deer because they follow a single dominant leader, the herdsman (Geist 1971). They now have a nearly ubiquitous worldwide distribution, and they are among the most abundant of all commensal animals. However, they have also become some of the most widespread invasive feral mammals, particularly on the 100 or more islands throughout the world where they have been introduced, causing severe damage to island ecosystems, in some cases for hundreds of years (Rudge 1984; Chynoweth 2013). Problems caused by feral goats and sheep are a subset of the larger problem of domestic livestock and natural systems. Feral goats are perhaps more widespread than feral sheep because goats have not been as highly modified by the process of domestication (Francis 2015).
The Bezoar ibex (Capra aegagrus) is the most likely ancestor of domestic goats (C. hircus) from both genetic and paleontological evidence (Pidancier et al. 2006). The domestication process started at least 10,000 years ago in highlands of western Iran, beginning with the selective harvesting of subadult males and the transition from hunting to herding of the species (Zeder and Hesse 2000). Multiple independent domestication events may have occurred or domestication may have incorporated multiple ancestral lineages (Pidancier et al. 2006). Traits selected during domestication include behavior, dairy, meat, skins, pelage color, mohair, cashmere, horns, pathogen resistance, and even intestines for catgut. Selection for reduced body size may have been related to the ability to better survive in hot and arid environments (Zeder 2009). A profound reduction in horn size occurred after humans began to control breeding, particularly in males, possibly associated with the absence of selective pressures for large horns used in mate competition (Zeder 2009)
Stochastic Population Dynamics of a Montane Ground-Dwelling Squirrel
Understanding the causes and consequences of population fluctuations is a central goal of ecology. We used demographic data from a long-term (1990–2008) study and matrix population models to investigate factors and processes influencing the dynamics and persistence of a golden-mantled ground squirrel (Callospermophilus lateralis) population, inhabiting a dynamic subalpine habitat in Colorado, USA. The overall deterministic population growth rate λ was 0.94±SE 0.05 but it varied widely over time, ranging from 0.45±0.09 in 2006 to 1.50±0.12 in 2003, and was below replacement (λ<1) for 9 out of 18 years. The stochastic population growth rate λs was 0.92, suggesting a declining population; however, the 95% CI on λs included 1.0 (0.52–1.60). Stochastic elasticity analysis showed that survival of adult females, followed by survival of juvenile females and litter size, were potentially the most influential vital rates; analysis of life table response experiments revealed that the same three life history variables made the largest contributions to year-to year changes in λ. Population viability analysis revealed that, when the influences of density dependence and immigration were not considered, the population had a high (close to 1.0 in 50 years) probability of extinction. However, probability of extinction declined to as low as zero when density dependence and immigration were considered. Destabilizing effects of stochastic forces were counteracted by regulating effects of density dependence and rescue effects of immigration, which allowed our study population to bounce back from low densities and prevented extinction. These results suggest that dynamics and persistence of our study population are determined synergistically by density-dependence, stochastic forces, and immigration
A 32-year demography of yellow-bellied marmots (Marmota flaviventris)
Yellow-bellied marmots Marmota flaviventris in the East River Valley of Colorado were live-trapped and individually marked annually from 1962 through 1993. These pooled data were used to produce a demography and life table for these years. Females had significantly better survivorship than males beyond the first-year age class, and the sex ratio became progressively female biased. The major mortality factors of predation and unsuccessful hibernation acted evenly on all age classes as shown by the constant rates of survivorship. The rate of senescence indicated that the probability of mortality did not increase with age. Females produced litters from ages 2 to 10 years. Mean litter size was 4.1 and did not differ among age classes. The female generation length of 4.49 years was 2.4 times the life expectancy and the median survivorship. The net reproductive rate (R-o) was 0.67, yet the population did not continually decline; adjustments to these data increased R-o to 0.85. Reproductive values (V-x) were approximately equal across the reproductive age classes. The polygynous mating system is both cause and effect of the demography. Marmot population size is affected by weather factors that influence reproduction and survival, by predation, and by movement into and out of the study area
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Differential investment in twin offspring by female pronghorns (Antilocapra americana)
Differential investment in offspring has been reported for many mammals, often in the context of the Trivers–
Willard model of male-biased investment, but evidence of differential investment in pronghorns (Antilocapra
americana) is largely lacking. We assessed the causes and consequences of different birth masses of littermate
fawns in a pronghorn population in Oregon. The mass differential for co-twins ranged from 0% to 89% (median
¼8.35%). Male-biased investment explained the mass differential in opposite-sex litters but not same-sex litters.
The mass differential did not result from mothers producing 1 normal-size fawn and 1 runt fawn, and the smaller
fawn was not deficient in physiological condition. Only 29% of fawns survived to 8 weeks and both fawns died
in 56% of litters, but co-twin mortalities were largely separate events. Mass did not confer a survival advantage
when considering all fawns through age 8 weeks, but there was evidence of such an advantage when comparing
fawns within litters before age 18 days. Differential investment in fawns might be a bet-hedging strategy in
which the mother accepts a lower expected reproductive success in exchange for a lower variance, but neither the
mean nor the variance differed between mothers of different-size (.8.35% mass differential) and similar-size
(,8.35%) litters. In fact, there was evidence of increased reproductive success for mothers of different-size
litters, much of which stemmed from higher survival 4–6 days after birth. Having different-size fawns reduced
the chances of sequential mortality, in which a predator killed one fawn then returned to kill the other.Keywords: Maternal investment, Sex-biased investment, Fawn survival, Antilocapra americana, Bet hedging, Win–stay strategy, Pronghorn, Body mas
Threat of Hantavirus Pulmonary Syndrome to Field Biologists Working with Small Mammals
Field biologists should use personal protective equipment appropriate for their activities
Temporal correlations among demographic parameters are ubiquitous but highly variable across species
Temporal correlations among demographic parameters can strongly influence
population dynamics. Our empirical knowledge, however, is very limited regarding
the direction and the magnitude of these correlations and how they vary among
demographic parameters and species’ life histories. Here, we use long-term
demographic data from 15 bird and mammal species with contrasting pace of life
to quantify correlation patterns among five key demographic parameters: juvenile and adult survival, reproductive probability, reproductive success and productivity.
Correlations among demographic parameters were ubiquitous, more frequently
positive than negative, but strongly differed across species. Correlations did not
markedly change along the slow-fast continuum of life histories, suggesting that
they were more strongly driven by ecological than evolutionary factors. As positive
temporal demographic correlations decrease the mean of the long-run population
growth rate, the common practice of ignoring temporal correlations in population
models could lead to the underestimation of extinction risks in most species
Bottlenecks and rescue effects in a fluctuating population of golden-mantled ground squirrels (Spermophilus lateralis)
Impacts of Feral Livestock on Island Watersheds
We assessed the effects of overgrazing by feral sheep on watersheds
on Santa Cruz Island, California. Overgrazing had a marked effect on stream
flow; flows were much greater in overgrazed than in lightly grazed watersheds
early in the rainy season, but the difference vanished later in the season. This
pattern can be explained by reduced infiltration and increased surface runoff of
rainfall in overgrazed areas. Thus, feral livestock may affect island species not
only directly by grazing and trampling, but also indirectly by altering hydrologic
processes and therefore species that are dependent on these processes
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