Community- and landscape-level responses of reptiles and small mammals to feral-horse grazing in the Great Basin

Beever, Erik A.; Brussard, Peter F.

doi:10.1016/j.jaridenv.2003.12.008

Cited by 62 publications

(73 citation statements)

References 40 publications

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“…In the USA, feral horses are federally managed and protected under the Free-Roaming Wild Horse and Burro Protection Act of 1971 and continue to overpopulate rangelands where they can negatively impact grasslands, riparian areas, soils and other wildlife 4 species (Rogers 1990;Beever and Brussard 2000;Levin et al 2002;Beever and Brussard 2004;Zalba and Cozzani 2004;Beever and Herrick 2006). Despite this trend, lethal control is largely unacceptable to the public.…”

Section: Introductionmentioning

confidence: 99%

Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

et al. 2010

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Context. Contraception is increasingly used as a management technique to reduce fertility in wildlife populations, but the feasibility of contraceptive formulations has been limited until recently as they have required multiple treatments to achieve prolonged infertility.Aims. We tested the efficacy and evaluated potential side effects of two contraceptive formulations, a porcine zona pellucida (PZP) formulation, SpayVac®, and a gonadotrophin releasing hormone (GnRH) formulation GonaCon-B™, in a population of free-roaming feral horses (Equus caballus). Both formulations were developed to provide several years of infertility with one injection. 2Methods. Females were treated in June 2005 with either GonaCon-B™ (n=24), SpayVac® (n=20), adjuvant only (n=22), or received no injection (n=18). Females were monitored for fertility status year round for three years post treatment.Key results. Both contraceptive treatments significantly reduced fertility for three years.Fertility rates for GonaCon-B™ mares were 39%, 42% and 31% respectively and 37%, 50%, and 44% for SpayVac® mares. During the same seasons, 61%, 67% and 76% of control females were fertile. We found no significant effects from contraceptive treatment on the sex ratio of foals, birthing season, or foal survival.Conclusions. These results demonstrate that both vaccines are capable of significantly reducing fertility for several years without boosters.Implications. Contraceptive vaccines examined in this study represent a useful tool for the management of feral horses, due to their being efficacious for three years in the absence of booster immunisations.

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Section: Introductionmentioning

confidence: 99%

Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

et al. 2010

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“…Reptiles were sampled within plots using visual based surveys. Reptile diversity was greater on average in areas without horse grazing than areas with horse grazing (Beever and Brussard, 2004). Also, seven of nine reptile species were more abundant in areas unoccupied by horses.…”

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confidence: 88%

“…Bock et al (1990) attributed the differences in bunchgrass lizard abundance to 1) the lack of bunch grasses in heavily grazed areas and 2) increased predation (bunchgrass lizards are relatively slow and require vegetative cover to escape from predators). Beever and Brussard (2004) studied the effects of feral horse grazing on both reptile and small mammal diversity and abundance in the Great Basin. Reptiles were sampled within plots using visual based surveys.…”

mentioning

confidence: 99%

“…Also, seven of nine reptile species were more abundant in areas unoccupied by horses. Despite these differences however, Beever and Brussard (2004) were reluctant to associate the differences with the presence of the horses. Instead they believed that an array of random factors could have produced the associations that they observed.…”

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confidence: 99%

“…A review by Germano et al (2001) Snakes are underrepresented in grazing studies. Only two studies (Beever and Brussard, 2004;Szaro et al, 1985) attempted to include snakes in their analyses and only Beever and Brussard (2004) attempted a snake community analysis. Snakes are traditionally viewed as poor study organisms for ecological, behavioral, and physiological research (Huey et al, 1983).…”

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confidence: 99%

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The Ecological Effects of Cattle Grazing on Reptiles and Small Mammals in a San Joaquin Valley Grassland

Tom¹

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Livestock grazing is a common and extensive land use practice in the United States occurring in a wide range of habitat types. As such, livestock grazing has the potential to alter ecosystem structure, function and community composition. The primary component (Chapter 1) of this thesis examined the effects of cattle grazing in a San Joaquin Valley grassland on two target taxa: reptiles and small mammals. The study took place on the Chimineas Unit of the Carrizo Ecological Reserve, San Luis Obispo County, California during Fall 2009 and Spring 2010. These taxa were sampled on matched pairs of two grazed and two ungrazed sites. Live trapping methods appropriate to sampling reptiles (coverboards and pit fall traps) and small mammals (Sherman live traps) were used to determine species richness and abundance of these taxa. Uta stansburiana (sideblotched lizard) abundances were greatest on Ungrazed1 (Fall: 1.75±0.49 captures/night, Spring: 3.58±0.35 captures/night). In addition, Chaetodipus californicus (Spiny pocket mouse) abundance was also greatest on Ungrazed1. Population estimates generated by Program CAPTURE suggest C. californicus could be 6.27 times more abundant on Ungrazed1 than Grazed1. However, sample size issues and site level effects confounded and made it difficult to determine significant differences between the grazed and ungrazed treatments for both reptile and small mammal taxa. Habitat structure at these sites was also evaluated including small mammal burrow abundance and vegetation structure. Again, differences between the grazed and ungrazed pasture could not be discerned because of site level effects occurring among matched pairs. As such, this thesis illustrates the difficulty in studying grazing and its potential effects on biotic systems because an array of variables can make unclear the differences between grazed and ungrazed areas. As a follow up study (Chapter 2) I used logistic regression to model U. stansburiana presence to examine possible sources of variation observed at trapping array locations utilized in the main study (Chapter 1). Shrubs exhibited a quasi-complete separation of data points and the three best models included: 1) Bare soil cover (AICc = 28.12), 2) Holes (AICc = 29.76), and 3) Bare soil cover + Holes (AICc = 29.90). Shrubs, bare soil cover and small mammal burrow density were all positively associated with U. stansburiana presence at array locations. Although species have general habitat requirements based upon their ecology and evolution, variations in habitat utilization exists depending upon the resources present at a specific location. Quantifying basic ecological information on a site specific basis is important to managing populations by identifying important resources and habitat components utilized by a given species on a given site. v ACKNOWLEDGMENTS

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Feral horses influence both spatial and temporal patterns of water use by native ungulates in a semi‐arid environment

et al. 2018

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Abstract. The horse (Equus caballus) is a feral ungulate that currently exceeds target population sizes in many areas of western North America. Horses are behaviorally dominant over native ungulates and outcompete the latter for access to water sources. However, a better understanding of the broader spatial and temporal implications of horse-induced competition on access to water by native ungulates will enable better conservation and management of native species. Our objective was to determine whether pronghorn (Antilocapra americana) and mule deer (Odocoileus hemionus) spatially or temporally altered their use of water to minimize interactions with horses. From 2010 to 2014, we used remote cameras to monitor ungulates at 32 water sources in the Great Basin Desert. We evaluated spatial and temporal partitioning by these species at water sources using generalized linear models, mixed-effects models, and Mann-Whitney U tests. We found that both native ungulates used water sources less often where horse activity at water sources was high, indicating that spatial avoidance occurred. Further, we observed significant differences in peak arrival time for pronghorn, but not mule deer at horse-occupied sites versus sites where horses were absent or uncommon, indicating that temporal avoidance may be more important for pronghorn than mule deer. Because mule deer are primarily crepuscular and nocturnal whereas horses are largely diurnal, we did not expect to observe a temporal shift for mule deer. We also found strong support for the interactive negative effect of elevated temperature and subsequent increased activity of horses at water sources on drinking patterns of pronghorn and mule deer. Our findings indicate that feral horses further constrain access to an already limited resource for native species in a semi-arid environment.

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Community- and landscape-level responses of reptiles and small mammals to feral-horse grazing in the Great Basin

Cited by 62 publications

References 40 publications

Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

Multi-year fertility reduction in free-roaming feral horses with single-injection immunocontraceptive formulations

The Ecological Effects of Cattle Grazing on Reptiles and Small Mammals in a San Joaquin Valley Grassland

Feral horses influence both spatial and temporal patterns of water use by native ungulates in a semi‐arid environment

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