scholarly journals Predation impedes recovery of Sierra Nevada bighorn sheep

2021 ◽  
pp. 444-470
Author(s):  
Daniel J. Gammons ◽  
Jeffrey L. Davis ◽  
David W. German ◽  
Kristin Denryter ◽  
John D. Wehausen ◽  
...  
Keyword(s):  
Population Growth ◽  
Sierra Nevada ◽  
Puma Concolor ◽  
Population Decline ◽  
Survival Rates ◽  
Bighorn Sheep ◽  
Ovis Canadensis ◽  
Management Actions ◽  
Near Future ◽  
Ovis Canadensis Sierrae

Translocation of animals into formerly occupied habitat is a key element of the recovery plan for Sierra Nevada bighorn sheep (Ovis canadensis sierrae), which are state (California) and federally listed as endangered. However, implementing Sierra bighorn translocations is a significant conservation challenge because of the small size of the extant population and the limited number of herds available to donate translocation stock. One such herd, the Mt. Langley herd, recently became unusable as a translocation source following a substantial population decline. At the time of listing in 1999, predation by mountain lions (Puma concolor; hereafter lion) was considered a primary threat to Sierra bighorn, and since then lion predation may have continued to limit the ability of source herds to provide translocation stock. We evaluated the relationship between lion predation and ewe survival rates within three source herds of the Southern Recovery Unit, compared lion abundance and ewe survival among years of varying predation levels, provided a range of estimated times for the Mt. Langley herd to recover to its former status as a translocation source, and determined if the rates lions have been removed to mitigate Sierra bighorn predation exceeded sustainable harvest guidelines. We found compelling evidence that lion predation has impeded the recovery of Sierra bighorn by reducing survival rates of adult ewes (and consequently, population growth) and by preying upon individuals that could have otherwise been translocated. Ewe survival was poor during years of extreme predation but even during years of typical predation, survival rates were below a level needed to ensure population growth, indicating that years with little or no lion predation may be necessary for the population to grow and meet recovery goals. Because the intensity of predation was related to lion abundance, monitoring lion populations could provide managers with advance warning of periods of extreme predation. We found that following a period of particularly extreme predation, the Mt. Langley herd decreased in abundance far below the threshold needed to be considered a source of translocation stock, resulting in the loss of approximately 25% of the recovery program’s capacity for translocations. It is unclear how many years it will take for this herd to recover, but management actions to reduce lion predation are likely needed for this herd to grow to a size that can afford to donate individuals to translocation efforts in the near future, even when optimistic growth rates are assumed. We found that lion removal may also be needed to prevent predation from leading to Sierra bighorn population decline. Lion removal rates that have been implemented thus far are well below what would be needed to reduce the abundance the eastern Sierra lion population itself. We recommend continued monitoring of Sierra bighorn and sympatric lions and note that lion removal may be required to facilitate bighorn recovery for the foreseeable future.

How plastic is migratory behavior? Quantifying elevational movement in a partially migratory alpine ungulate, the Sierra Nevada bighorn sheep (Ovis canadensis sierrae)

2018 ◽  
Vol 96 (12) ◽  
pp. 1385-1394 ◽  
Author(s):  
D.B. Spitz ◽  
M. Hebblewhite ◽  
T.R. Stephenson ◽  
D.W. German
Keyword(s):  
Sierra Nevada ◽  
Nonlinear Modeling ◽  
Bighorn Sheep ◽  
Ovis Canadensis ◽  
Migratory Behavior ◽  
Conditional Strategy ◽  
Individual Level ◽  
Migratory Status ◽  
The Individual ◽  
Ovis Canadensis Sierrae

Migratory species face well-documented global declines, but the causes of these declines remain unclear. One obstacle to better understanding these declines is uncertainty surrounding how migratory behavior is maintained. Most migratory populations are partially migratory, displaying both migrant and resident behaviors. Theory only provides two possible explanations for this coexistence of migration and residency: either these behaviors are fixed at the individual level or both behaviors are part of a single conditional strategy in which an individual’s migratory status (adoption of migrant or resident behavior) is plastic. Here we test for plasticity in migratory status and tactics (timing, distance, and duration of migration) in a federally endangered mountain caprid, the Sierra Nevada bighorn sheep (Ovis canadensis sierrae Grinnell, 1912). We used nonlinear modeling to quantitatively describe migratory behavior, analyzing 262 animal-years of GPS location data collected between 2005 and 2016 from 161 females across 14 subpopulations. Migratory tactics and prevalence varied by subpopulation. On average, individuals from partially migratory subpopulations switched migratory status every 4 years. Our results support the hypothesis that partial migration is maintained through a single conditional strategy. Understanding plasticity in migratory behavior will improve monitoring efforts and provide a rigorous basis for evaluating threats, particularly those associated with changing climate.

scholarly journals Sexual Segregation in Sierra Nevada Bighorn Sheep, Ovis canadensis sierrae: Ramifications for Conservation

2010 ◽  
Vol 42 (4) ◽  
pp. 476-489 ◽  
Author(s):  
Cody A. Schroeder ◽  
R. Terry Bowyer ◽  
Vernon C. Bleich ◽  
Thomas R. Stephenson
Keyword(s):  
Sierra Nevada ◽  
Bighorn Sheep ◽  
Ovis Canadensis ◽  
Sexual Segregation ◽  
Ovis Canadensis Sierrae

Using population dynamics modelling to evaluate potential success of restoration: a case study of a Hawaiian vine in a changing climate

2014 ◽  
Vol 42 (1) ◽  
pp. 20-30 ◽  
Author(s):  
TAMARA M. WONG ◽  
TAMARA TICKTIN
Keyword(s):  
Population Growth ◽  
Growth Rates ◽  
Key Management ◽  
Demographic Data ◽  
Population Decline ◽  
Management Strategies ◽  
Survival Rates ◽  
Population Modelling ◽  
Population Growth Rates

SUMMARYDemographic comparisons between wild and restored populations of at-risk plant species can reveal key management strategies for effective conservation, but few such studies exist. This paper evaluates the potential restoration success ofAlyxia stellata, a Hawaiian vine. Stage-structured matrix projection models that compared long-term and transient dynamics of wild versus restoredA. stellatapopulations, and restored populations under different levels of canopy cover, were built from demographic data collected over a four year period. Stochastic models of wild populations projected stable or slightly declining long-term growth rates depending on frequency of dry years. Projected long-term population growth rates of restored populations were significantly higher in closed than open canopy conditions, but indicated population decline under both conditions. Life table response experiments illustrated that lower survival rates, especially of small adults and juveniles, contributed to diminished population growth rates in restored populations. Transient analyses for restored populations projected short-term decline occurring even faster than predicted by asymptotic dynamics. Restored populations will not be viable over the long term under conditions commonly found in restoration projects and interventions will likely be necessary. This study illustrates how the combination of long-term population modelling and transient analyses can be effective in providing relevant information for plant demographers and restoration practitioners to promote self-sustaining native populations, including under future climates.

A comparative study of survival, recruitment and population growth in two translocated populations of the threatened greater bilby (Macrotis lagotis)

2020 ◽  
Vol 47 (5) ◽  
pp. 415
Author(s):  
Karleah K. Berris ◽  
Steven J. B. Cooper ◽  
William G. Breed ◽  
Joshua R. Berris ◽  
Susan M. Carthew
Keyword(s):  
Population Growth ◽  
Habitat Degradation ◽  
Mammalian Species ◽  
Survival Rates ◽  
Previous History ◽  
Feral Cats ◽  
Offshore Island ◽  
Management Actions ◽  
History Of ◽  
European Rabbits

Abstract Context Translocations have been widely used to re-establish populations of threatened Australian mammalian species. However, they are limited by the availability of sites where key threats can be effectively minimised or eliminated. Outside of ‘safe havens’, threats such as exotic predators, introduced herbivores and habitat degradation are often unable to be completely eliminated. Understanding how different threats affect Australian mammal populations can assist in prioritising threat-management actions outside of safe havens. AimsWe sought to determine whether translocations of the greater bilby to two sites in the temperate zone of South Australia could be successful when human-induced threats, such as prior habitat clearance, historic grazing, the presence of feral cats and European rabbits, could not be completely eliminated. Methods Greater bilbies were regularly cage trapped at two translocation sites and a capture–mark–recapture study was used to determine survival, recruitment and population growth at both sites. Key results Our study showed that bilbies were successfully translocated to an offshore island with a previous history of grazing and habitat clearance, but which was free of exotic predators. At a second site, a mainland exclosure with feral cats and European rabbits present, the bilby population declined over time. Adult bilbies had similar survival rates in both populations; however, the mainland bilby population had low recruitment rates and low numbers of subadults despite high adult female fecundity. ConclusionsThe results indicated that past grazing and habitat clearance did not prevent the bilby population on the offshore island establishing and reaching a high population density. In the mainland exclosure, the low recruitment is probably due to feral cats predating on subadult bilbies following pouch emergence. Implications The results demonstrated that the bilby, an ecologically flexible Australian marsupial, can be successfully translocated to sites with a history of habitat degradation if exotic predators are absent. At the mainland exclosure site, threat mitigation for bilbies should focus on control or eradication of the feral cats. The control of European rabbits without control of feral cats could lead to prey-switching by feral cats, further increasing predation pressure on the small bilby population.

scholarly journals The viability of pronatalism as a response to population growth decline in the Canadian context

2021 ◽  
Author(s):  
Katharine Emma Blair
Keyword(s):  
Population Growth ◽  
Labour Force ◽  
Population Decline ◽  
Labour Force Participation ◽  
Long Term Effects ◽  
Demographic Trends ◽  
Canadian Context ◽  
Growth Decline ◽  
Near Future

A decrease in fertility over the last thirty years has led to projections for population growth decline and possible population decline in the near future. Although immigration has traditionally been seen as a source of growth for Canada, current demographic trends suggest a more comprehensive approach may be needed. A pronatalist policy may help offset the long term effects of population decline if used in tandem with increased immigration and increased support for arriving immigrants. In order to be successful such a policy would need to address both the direct and indirect barriers to fertility as experienced by women and families while encouraging increased labour force participation by women.

Temporal geographic variation in the lambing season of bighorn sheep

1982 ◽  
Vol 60 (8) ◽  
pp. 1781-1793 ◽  
Author(s):  
Richard W. Thompson ◽  
Jack C. Turner
Keyword(s):  
Plant Growth ◽  
Geographic Variation ◽  
Sierra Nevada ◽  
National Parks ◽  
Bighorn Sheep ◽  
Ovis Canadensis ◽  
Vegetative Development ◽  
Growing Seasons ◽  
Environmental Regimes ◽  
Sierra Nevada Mountains

Temporal geographic variation in lambing seasons was statistically assessed for 22 populations, including 5 ecological races, of North American bighorn sheep (Ovis canadensis ssp.) from the Canadian National Parks (52° N) to western Texas (30° N). Throughout their distribution, bighorn lambing occurs coincident with the period of vegetative development when the environmental regime ameliorates neonate survival. Analyses generally demonstrate later and shorter lambing seasons in higher latitudinal populations (P < 0.001). Inception of lambing occurs later with colder temperatures, increased snowfall, at higher latitudes and elevations, and with later and shorter growing seasons [Formula: see text]. Additionally, a significant (P < 0.001) divergence in the reproductive "strategy" (median onset and duration of lambing) exists between bighorn herds of the Sierra Nevada Mountains, California (37° N) and the Desert National Wildlife Range, Nevada (36° N) as a result of two distinct, but adjacent environmental regimes. Lambing in northern populations is cued to a brief, relatively predictable period of plant growth. Southern bighorn protract lambing such that some recruitment coincides with relatively unpredictable plant growth, triggered by erratic rains.

scholarly journals An efficient method of evaluating multiple concurrent management actions on invasive populations

2021 ◽  
Author(s):  
Amy Jane Davis ◽  
Randy O Farrar ◽  
Brad Jump ◽  
Parker T Hall ◽  
Travis Guerrant ◽  
...  
Keyword(s):  
Invasive Species ◽  
Population Growth ◽  
Population Decline ◽  
Species Abundance ◽  
Management Effectiveness ◽  
Feral Swine ◽  
Management Efficiency ◽  
Management Actions ◽  
Spatial Coverage ◽  
Management Effort

Evaluation of the efficacy of management actions to control invasive species is crucial for maintaining funding and to provide feedback for the continual improvement of management efficiency. However, it is often difficult to assess the efficacy of control methods due to limited resources for monitoring. To evaluate management actions there is often a trade-off in effort aimed at performing management actions and effort aimed at collecting monitoring data to evaluate management actions. We developed a method to estimate invasive species abundance, evaluate management effectiveness, and evaluate population growth overtime from a combination of removal activities (e.g., aerial gunning, trapping, ground shooting) using only data collected during removal efforts (the method of removal, the date, location, number of animals removed, and the effort). This dynamic approach allows for estimating abundance at discrete time points and the estimation of population growth between removal periods. We applied this method to removal data from Mingo National Wildlife Refuge in Missouri from December 2015 to September 2019, where the management objective is elimination. Populations of feral swine on Mingo NWR have fluctuated over time but have shown more marked declines in the last 3-6 months. More dramatic declines were observed in the center of the refuge. To counteract population growth (from both births and immigration) the percent of the population of feral swine removed monthly must be greater than the growth rate. On average, we found that removing 10% of the population monthly had only a 50% chance of causing a population decline, whereas removing 15% of the population monthly had a 95% chance of causing a population decline. Our method provides advancement over traditional removal modeling approaches because it can be applied to evaluate management programs that use a broad range of removal techniques concurrently and whose management effort and spatial coverage vary across time.

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