Abstract
Interactions between large herbivores and their food supply are central to the study of population dynamics. We assessed temporal and spatial patterns in meadow plant biomass over a 23-year period for meadow complexes that were spatially linked to three distinct populations of Roosevelt elk (Cervus elaphus roosevelti) in northwestern California. Our objectives were to determine whether the plant community exhibited a tolerant or resistant response when elk population growth became irruptive. Plant biomass for the three meadow complexes inhabited by the elk populations was measured using Normalized Difference Vegetation Index (NDVI), which was derived from Landsat 5 Thematic Mapper imagery. Elk populations exhibited different patterns of growth through the time series, whereby one population underwent a complete four-stage irruptive growth pattern while the other two did not. Temporal changes in NDVI for the meadow complex used by the irruptive population suggested a decline in forage biomass during the end of the dry season and a temporal decline in spatial variation of NDVI at the peak of plant biomass in May. Conversely, no such patterns were detected in the meadow complexes inhabited by the nonirruptive populations. Our findings suggest that the meadow complex used by the irruptive elk population may have undergone changes in plant community composition favoring plants that were resistant to elk grazing.
Highlights
Free-ranging continental populations of ungulates have traditionally been understood to display a “logistic” growth curve, increasing from a small population size to a larger population size that is relatively stable near the carrying capacity (K) of the habitat
Ecology and Evolution published by John Wiley & Sons Ltd
Across the time series of population data (1997–2013), population dynamics of the nonirruptive Bald Hills and Boyes populations were dissimilar in shape (Fig. 3)
Summary
Free-ranging continental populations of ungulates have traditionally been understood to display a “logistic” growth curve, increasing from a small population size to a larger population size that is relatively stable near the carrying capacity (K) of the habitat. The population fluctuates around an equilibrium with the food supply, with relatively small annual changes resulting from variation in recruitment, mortality and movement due to climatic conditions (Coulson et al 2000; Eberhardt 2002; Bonenfant et al 2009). Another pattern of population growth in ungulates, irruption, has been well documented in numerous populations of large ungulates inhabiting oceanic islands (Scheffer 1951; Klein 1968; Caughley 1970; LeaderWilliams 1980; Ricca et al 2014).
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