Abstract
Coyotes (Canis latrans) play a keystone role in the population regulation of microherbivores and mesopredators in certain ecosystems. Despite this fact, coyote control measures still are implemented.
We evaluated the effects of removing coyotes on sympatric populations of rodents, lagomorphs, raptors, and mammalian mesopredators in a shortgrass prairie ecosystem of western Texas. Faunal communities were examined on 2 treatment and 2 comparison 5,000-ha sites of mixed grassland and shrubland habitats for 1 year before coyote removal and for 2 years during coyote removal. We removed 354 coyotes by aerial gunning on treatment sites. Removal efforts were initiated every third month from April 1990 to January 1992. Coyote density was reduced from 0.12 ± 0.01 (x̄ ± SE) to 0.06 ± 0.01 coyotes/km2 on treatment sites.
Density on comparison sites remained stable at 0.14 ± 0.01 coyotes/km2. We found no differences in faunal population estimates between comparison and treatment sites for the year before coyote removal.
Within 9 months following the initiation of coyote removal, rodent species richness and rodent diversity declined on treatment sites. Without coyote predation, the Ord's kangaroo rat (Dipodomys ordii) became the most abundant rodent in shrublands and was the only rodent species caught in grasslands after 12 months of coyote removal.
Rodent density and biomass, black-tailed jackrabbit (Lepus californicus) density, and relative abundance of badgers (Taxidea taxus), bobcats (Felis rufus), and gray foxes (Urocyon cineroargenteus) increased on treatment sites.
Variation in the density of desert cottontail rabbits (Sylvilagus audubonii) and raptor richness, diversity, and density was not related to coyote density. Our findings were consistent with the predator-mediated coexistence hypothesis, which suggests that a keystone predator (coyote) can influence faunal community structure.
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Coyote control breeds small predators
Removing the coyote as a "keystone predator" reduces diversity of small mammal prey species and increases the presence of small predators like skunks, badgers and bobcats, according to a Texas study.
Scott Henke and Fred Bryant of the Cesar Kleberg Wildlife Research Institute in Kingsville, Texas, conducted a study of coyotes as keystone predators on four 5,000 hectare sites in western Texas. Two of the sites were kept coyote-free by aerial gunning; the other two were left alone for normal coyote predation.
Scott Henke and Fred Bryant of the Cesar Kleberg Wildlife Research Institute in Kingsville, Texas, conducted a study of coyotes as keystone predators on four 5,000 hectare sites in western Texas. Two of the sites were kept coyote-free by aerial gunning; the other two were left alone for normal coyote predation.
A keystone predator is one that is considered to be at the top of the food chain, and it is more than a little unusual to see scientists study coyotes as if they occupied the same lordly position as wolves, grizzlies and cougars.
Mark Twain once wrote that the coyote "is a living, breathing allegory of Want. He is always hungry. He is always poor, out of luck and friendless. The meanest creatures despise him and even the fleas would desert him for a velocipede." (You probably have a velocipede in your garage. It's a bicycle.)The results of the study indicate that coyotes may deserve at least a minor rung on the ladder of predatory nobility. They seem to exert "a top-down influence in their prey community," according to the researchers.In the study areas, there were originally 11 kinds of rodents in residence. Nine months after coyotes were removed, only one rodent species remained: Ord's kangaroo rats. "Rodent species richness and and diversity declined on treatment sites," Henke said, "while rodent density, rodent biomass and percentage of Ord's kangaroo rats within rodent composition increased on treatment sites."
In other words, there was a larger number of rodents on the coyote-free sites, but there was only one species where there had been 11.
In addition, the black-tailed jackrabbits increased from three- to 18-fold on the test plots without coyotes. Cottontails, however, showed no changes based on the presence or absence of coyotes.
The study also looked at the abundance of raptors and "mesopredators," smaller predators such as gray foxes, badgers, skunks and bobcats.
The study found almost no change in the number or mix of the 14 species of raptors, owls and scavengers that used the areas, whether or not the coyotes were present.
However, Henke said, the small predators increased dramatically in the absence of coyotes. All four of the species mentioned above showed a dramatic increase in their presence on the coyote-free areas.
Coyote removal, which any sheepman can tell you requires a herculean effort, occurred once every three months from April 1990 to January 1992. Some 354 coyotes were killed on treatment sites, but the overall coyote population was only reduced by about 50 percent. Coyotes migrate easily into areas unoccupied by other coyote packs. Such was the case in the study areas, despite the aerial gunning.
Henke said he was surprised that the Ord's kangaroo rat turned out to be the species that benefited most from coyote depopulation. But he noted that the last months of the study coincided with a drier than normal period in western Texas, and that coyotes are well-adapted to dry conditions.
Mark Twain once wrote that the coyote "is a living, breathing allegory of Want. He is always hungry. He is always poor, out of luck and friendless. The meanest creatures despise him and even the fleas would desert him for a velocipede." (You probably have a velocipede in your garage. It's a bicycle.)The results of the study indicate that coyotes may deserve at least a minor rung on the ladder of predatory nobility. They seem to exert "a top-down influence in their prey community," according to the researchers.In the study areas, there were originally 11 kinds of rodents in residence. Nine months after coyotes were removed, only one rodent species remained: Ord's kangaroo rats. "Rodent species richness and and diversity declined on treatment sites," Henke said, "while rodent density, rodent biomass and percentage of Ord's kangaroo rats within rodent composition increased on treatment sites."
In other words, there was a larger number of rodents on the coyote-free sites, but there was only one species where there had been 11.
In addition, the black-tailed jackrabbits increased from three- to 18-fold on the test plots without coyotes. Cottontails, however, showed no changes based on the presence or absence of coyotes.
The study also looked at the abundance of raptors and "mesopredators," smaller predators such as gray foxes, badgers, skunks and bobcats.
The study found almost no change in the number or mix of the 14 species of raptors, owls and scavengers that used the areas, whether or not the coyotes were present.
However, Henke said, the small predators increased dramatically in the absence of coyotes. All four of the species mentioned above showed a dramatic increase in their presence on the coyote-free areas.
Coyote removal, which any sheepman can tell you requires a herculean effort, occurred once every three months from April 1990 to January 1992. Some 354 coyotes were killed on treatment sites, but the overall coyote population was only reduced by about 50 percent. Coyotes migrate easily into areas unoccupied by other coyote packs. Such was the case in the study areas, despite the aerial gunning.
Henke said he was surprised that the Ord's kangaroo rat turned out to be the species that benefited most from coyote depopulation. But he noted that the last months of the study coincided with a drier than normal period in western Texas, and that coyotes are well-adapted to dry conditions.
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