Modeling effects of harvest on firefly population persistence

Abstract

North American fireflies in the genus Photinus are commercially harvested to extract the enzyme luciferase, despite the availability of a synthetic recombinant enzyme. Our goal was to examine the potential effects of harvesting on Photinus population persistence. Using estimated demographic parameters for Photinus, we developed a stochastic simulation population model to understand combined effects of demography, harvest rate, delayed larval development, and environmental stochasticity on population persistence of fireflies. With no harvest and low environmental stochasticity, modeled populations tended to reach carrying capacity. We found that average population size of adult fireflies decreased with increasing harvest rate and increasing environmental stochasticity. At the highest modeled growth rate (λ=2.8) the population failed to persist only when environmental stochasticity was high and harvest rate was ≥60%. Once harvest was introduced, only populations with high growth rates consistently persisted. Long-term, sustainable Photinus harvest rates based on survey data suggest that harvest rates >10% are acceptable only if λ>1.6. Our modeling results suggest that Photinus populations might tolerate low harvest levels, although in the absence of more precise data on vital rates and the amount of environmental stochasticity, the exact level is unknown. To further examine sustainability, harvest rates should be monitored and standardized surveys conducted to document firefly population changes.