Population density of North American elk: effects on plant diversity

Abstract

Large, herbivorous mammals have profound effects on ecosystem structure and function and often act as keystone species in ecosystems they inhabit. Density-dependent processes associated with population structure of large mammals may interact with ecosystem functioning to increase or decrease biodiversity, depending on the relationship of herbivore populations relative to the carrying capacity (K) of the ecosystem. We tested for indirect effects of population density of large herbivores on plant species richness and diversity in a montane ecosystem, where increased net aboveground primary productivity (NAPP) in response to low levels of herbivory has been reported. We documented a positive, linear relationship between plant-species diversity and richness with NAPP. Structural equation modeling revealed significant indirect relationships between population density of herbivores, NAPP, and species diversity. We observed an indirect effect of density-dependent processes in large, herbivorous mammals and species diversity of plants through changes in NAPP in this montane ecosystem. Changes in species diversity of plants in response to herbivory may be more indirect in ecosystems with long histories of herbivory. Those subtle or indirect effects of herbivory may have strong effects on ecosystem functioning, but may be overlooked in plant communities that are relatively resilient to herbivory.

Habitat Interference by Axis Deer on White‐Tailed Deer

“…The experimental manipulation of high and low population density began in 1999, but a gate was left open between study areas. Thus, elk densities were moderately high (10.8 elk/km 2 ) and low (6.6 elk/ km 2 ; Stewart et al 2006Stewart et al , 2009. Finally in 2000 and 2001, we restricted access to our study areas and maintained our targeted high (20.1 elk/km 2 ) and low (4.1 elk/km 2 ) densities of elk (Stewart et al 2006).…”

“…We restricted our experiment to the northeast area on Starkey, which encompassed 1,452 ha and was separated from the remainder of our study area by a high fence (Stewart et al 2002(Stewart et al , 2006(Stewart et al , 2009. This northeast area was divided into two study sites with the same 2.4-m high fence, east (842 ha) and west (610 ha), to accommodate experimental comparisons of two populations densities of elk (Stewart et al 2006(Stewart et al , 2009.…”

“…This northeast area was divided into two study sites with the same 2.4-m high fence, east (842 ha) and west (610 ha), to accommodate experimental comparisons of two populations densities of elk (Stewart et al 2006(Stewart et al , 2009. We divided the northeast area in a manner that resulted in plant communities being near equal in proportions in the east and west study areas (Stewart et al 2005(Stewart et al , 2006.…”

“…Functional groups of plants included forbs, grasses, sedges, mat-forming shrubs, such as twinflower Linnaea borealis, and upright shrubs, such as serviceberry Amelanchier alnifolia. Plant nomenclature follows Hitchcock & Cronquist (1996) Experimental design During 1997, we began an experiment to examine effects of population density of elk on their physical condition and reproduction (Stewart et al 2005) and on ecosystem processes (Stewart et al 2006(Stewart et al , 2009. We created two populations of elk at high and low density relative to carrying capacity (K), in the northeast east and west study areas on Starkey.…”

“…The high-density population was maintained near K (20.1 elk/km 2 ) based on physical condition of elk on Starkey. At low densities of elk, near or below maximum sustained yield, we set the density of elk at 4.1 elk/km 2 (Stewart et al 2006(Stewart et al , 2009. The highdensity population was randomly assigned to the northeast study area and the low-density population to the northwest study area.…”