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Deer dietary responses to wildfire: optimal foraging, individual specialization, or opportunism?

White, Carly1; Bush, Josh2; Sacks, Benjamin1

Published Feb 29, 2024 on Dryad. https://doi.org/10.5061/dryad.3ffbg79q7

Data files

Feb 29, 2024 version files 783.74 MB

Abstract

Increasing impacts of wildfire on arid regions of the world fueled by climate change highlight the need to better understand how natural communities respond to fire.  While plant communities have received much attention, less is known about responses of keystone herbivores, such as ungulates.  Large herbivores may temporarily vacate burned areas as vegetation decreases, returning as vegetation recovers, and concentrating in burn areas as early successional herbaceous species begin to flourish.  However, few data exist to assess herbivore trophic niches in burned and unburned habitats.  We took advantage of a large (1,660-km2) wildfire that erupted in northern California during an in-progress study of black-tailed deer (Odocoileus hemionus columbianus) to investigate deer use of and diets within burned and unburned habitats before and after the fire.  Depending on whether deer diet selection conformed better to optimal foraging models (including the niche variation hypothesis), or to that of a generalist forager, we expected that dietary breadth would either increase or decrease, respectively, in direct response to the reduction in forage associated with the fire and then decrease or increase again as the plant community recovered.  We used fecal pellet counts and metabarcoding to document changes in habitat use and diet relative to the fire. Pellet counts supported predictions that deer increased use of unburned sites and reduced use of burn sites after the fire and began to return to burned sites in subsequent sampling years.  Diet diversity did not differ significantly between control and burn sites before the fire, but was lower in burn than control sites post-fire (P < 0.001), when and where diet was dominated by oak (Quercus spp).  In contrast, during subsequent years, diet diversity was higher (including more herbaceous plants) in burn than control sites (P < 0.05). In contrast to predictions of optimal foraging and niche variation hypotheses, individual deer foraged as generalists for which diversity of the plant community as determined by fire was the primary determinant of their dietary niche breadth.