Understanding the effects of mass mortality events on plant communities and consumer behavior
Embargo TypeVisible to MSU only for 1 Year
Embargo Lift Date10000-01-01
Mass mortality events (MMEs) are die-offs that result in increased carrion biomass and sometimes the impairment of functional roles. Concurrently, several vulture species are declining. Carrion is a basal resource in ecosystems and its recycling by vultures is considered an ecosystem service. However, the consequences of simultaneously increasing carrion loads and declining vulture populations are unknown. I developed a theoretical framework predicting that, with increasing carrion biomass, carrion food web diversity would increase horizontally and vertically, respectively increasing and decreasing carrion recycling efficiency. Using a manipulative experiment, I investigated the role of bottom-up and top-down forces affecting plant communities during an MME. I selected 5 sites to establish 6 treatments crossing different levels of carrion addition and nutrient addition, and control with vertebrate scavenger and herbivore access. I transplanted six cherrybark oak (Quercus pagoda) seedlings to each plot, protecting half of them from herbivory. Carrion biomass shifted dominance of plant functional groups to favor annual plants, an effect reduced by scavenger access. Herbivore access affected plant community response to carrion and limited growth and survival of transplanted seedlings regardless of treatment. Nutrient addition did not affect plant communities, growth, and survival suggesting that MME effects on plants are likely mediated primarily by top-down forces. To determine if behavioral plasticity of vultures affects carrion recycling efficiency, I monitored turkey (Cathartes aura) and black (Coragyps atratus) vulture behavior. Both species increased group size, but only black vultures increased individuals feeding per group and activity overlap between species increased with increasing carrion biomass. As a result, estimated carrion consumption by vultures increased with carrion biomass suggesting behavioral plasticity may alleviate some of the effects of vulture declines on carrion recycling. Finally, vultures compete with invertebrate scavengers so declining vultures may release their populations to compensate for the loss. However, in one of my experiments, variation in vulture visitation was negatively correlated with the abundance of blowflies parasitized by Entomophthora sp. Our observations may suggest that vultures were more likely mediating carrion decomposition affecting parasitism, which may limit blowflies from compensating for declining vultures.