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Managing more than the mean: using quantile regression to identify factors related to large elk groups

View Article: PubMed Central - PubMed

ABSTRACT

Animal group size distributions are often right‐skewed, whereby most groups are small, but most individuals occur in larger groups that may also disproportionately affect ecology and policy. In this case, examining covariates associated with upper quantiles of the group size distribution could facilitate better understanding and management of large animal groups.

We studied wintering elk groups in Wyoming, where group sizes span several orders of magnitude, and issues of disease, predation and property damage are affected by larger group sizes. We used quantile regression to evaluate relationships between the group size distribution and variables of land use, habitat, elk density and wolf abundance to identify conditions important to larger elk groups.

We recorded 1263 groups ranging from 1 to 1952 elk and found that across all quantiles of group size, group sizes were larger in open habitat and on private land, but the largest effect occurred between irrigated and non‐irrigated land [e.g. the 90th quantile group size increased by 135 elk (95% CI = 42, 227) on irrigation].

Only upper quantile group sizes were positively related to broad‐scale measures of elk density and wolf abundance. For wolf abundance, this effect was greater on elk groups found in open habitats and private land than those in closed habitats or public land. If we had limited our analysis to mean or median group sizes, we would not have detected these effects.

Synthesis and applications. Our analysis of elk group size distributions using quantile regression suggests that private land, irrigation, open habitat, elk density and wolf abundance can affect large elk group sizes. Thus, to manage larger groups by removal or dispersal of individuals, we recommend incentivizing hunting on private land (particularly if irrigated) during the regular and late hunting seasons, promoting tolerance of wolves on private land (if elk aggregate in these areas to avoid wolves) and creating more winter range and varied habitats. Relationships to the variables of interest also differed by quantile, highlighting the importance of using quantile regression to examine response variables more completely to uncover relationships important to conservation and management.

Synthesis and applications. Our analysis of elk group size distributions using quantile regression suggests that private land, irrigation, open habitat, elk density and wolf abundance can affect large elk group sizes. Thus, to manage larger groups by removal or dispersal of individuals, we recommend incentivizing hunting on private land (particularly if irrigated) during the regular and late hunting seasons, promoting tolerance of wolves on private land (if elk aggregate in these areas to avoid wolves) and creating more winter range and varied habitats. Relationships to the variables of interest also differed by quantile, highlighting the importance of using quantile regression to examine response variables more completely to uncover relationships important to conservation and management.

No MeSH data available.


Related in: MedlinePlus

Map of the 10 elk hunt areas, aerial survey transects and elk groups. Hunt areas are labelled as 50, 51, 52, 54, 121, 59, 63, 67, 25 and 99. Panels a–c correspond to labelled areas in the upper left map. YNP, Yellowstone National Park; Elev, elevation.
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jpe12514-fig-0001: Map of the 10 elk hunt areas, aerial survey transects and elk groups. Hunt areas are labelled as 50, 51, 52, 54, 121, 59, 63, 67, 25 and 99. Panels a–c correspond to labelled areas in the upper left map. YNP, Yellowstone National Park; Elev, elevation.

Mentions: We measured elk group size and environmental variables in 10 elk hunt areas in western Wyoming (Fig. 1) from January through May in 2010, 2011 and 2012. These months encompass the period when B. abortus is most likely to be transmitted among elk (Roffe et al. 2004) and when most elk have moved to mountain foothills and valley bottoms to avoid snow at higher elevations. The hunt areas in our study were selected because their annual elk densities, wolf numbers and brucellosis seroprevalence in elk spanned the range of values found across the broader GYA region. Elk densities ranged from 0·2 to 3·0 elk km−2 [Wyoming Game and Fish Department (WGFD) (2011)], wolf numbers ranged from 0 to 18 wolves per year (USFWS et al. 2011), and brucellosis seroprevalence ranged from 0 to 25% (Cross et al. 2010; Scurlock & Edwards 2010). Our study area did not contain feedgrounds where elk are supplementally fed during the winter.


Managing more than the mean: using quantile regression to identify factors related to large elk groups
Map of the 10 elk hunt areas, aerial survey transects and elk groups. Hunt areas are labelled as 50, 51, 52, 54, 121, 59, 63, 67, 25 and 99. Panels a–c correspond to labelled areas in the upper left map. YNP, Yellowstone National Park; Elev, elevation.
© Copyright Policy - creativeCommonsBy-nc-nd
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016784&req=5

jpe12514-fig-0001: Map of the 10 elk hunt areas, aerial survey transects and elk groups. Hunt areas are labelled as 50, 51, 52, 54, 121, 59, 63, 67, 25 and 99. Panels a–c correspond to labelled areas in the upper left map. YNP, Yellowstone National Park; Elev, elevation.
Mentions: We measured elk group size and environmental variables in 10 elk hunt areas in western Wyoming (Fig. 1) from January through May in 2010, 2011 and 2012. These months encompass the period when B. abortus is most likely to be transmitted among elk (Roffe et al. 2004) and when most elk have moved to mountain foothills and valley bottoms to avoid snow at higher elevations. The hunt areas in our study were selected because their annual elk densities, wolf numbers and brucellosis seroprevalence in elk spanned the range of values found across the broader GYA region. Elk densities ranged from 0·2 to 3·0 elk km−2 [Wyoming Game and Fish Department (WGFD) (2011)], wolf numbers ranged from 0 to 18 wolves per year (USFWS et al. 2011), and brucellosis seroprevalence ranged from 0 to 25% (Cross et al. 2010; Scurlock & Edwards 2010). Our study area did not contain feedgrounds where elk are supplementally fed during the winter.

View Article: PubMed Central - PubMed

ABSTRACT

Animal group size distributions are often right‐skewed, whereby most groups are small, but most individuals occur in larger groups that may also disproportionately affect ecology and policy. In this case, examining covariates associated with upper quantiles of the group size distribution could facilitate better understanding and management of large animal groups.

We studied wintering elk groups in Wyoming, where group sizes span several orders of magnitude, and issues of disease, predation and property damage are affected by larger group sizes. We used quantile regression to evaluate relationships between the group size distribution and variables of land use, habitat, elk density and wolf abundance to identify conditions important to larger elk groups.

We recorded 1263 groups ranging from 1 to 1952 elk and found that across all quantiles of group size, group sizes were larger in open habitat and on private land, but the largest effect occurred between irrigated and non‐irrigated land [e.g. the 90th quantile group size increased by 135 elk (95% CI = 42, 227) on irrigation].

Only upper quantile group sizes were positively related to broad‐scale measures of elk density and wolf abundance. For wolf abundance, this effect was greater on elk groups found in open habitats and private land than those in closed habitats or public land. If we had limited our analysis to mean or median group sizes, we would not have detected these effects.

Synthesis and applications. Our analysis of elk group size distributions using quantile regression suggests that private land, irrigation, open habitat, elk density and wolf abundance can affect large elk group sizes. Thus, to manage larger groups by removal or dispersal of individuals, we recommend incentivizing hunting on private land (particularly if irrigated) during the regular and late hunting seasons, promoting tolerance of wolves on private land (if elk aggregate in these areas to avoid wolves) and creating more winter range and varied habitats. Relationships to the variables of interest also differed by quantile, highlighting the importance of using quantile regression to examine response variables more completely to uncover relationships important to conservation and management.

Synthesis and applications. Our analysis of elk group size distributions using quantile regression suggests that private land, irrigation, open habitat, elk density and wolf abundance can affect large elk group sizes. Thus, to manage larger groups by removal or dispersal of individuals, we recommend incentivizing hunting on private land (particularly if irrigated) during the regular and late hunting seasons, promoting tolerance of wolves on private land (if elk aggregate in these areas to avoid wolves) and creating more winter range and varied habitats. Relationships to the variables of interest also differed by quantile, highlighting the importance of using quantile regression to examine response variables more completely to uncover relationships important to conservation and management.

No MeSH data available.


Related in: MedlinePlus