Global patterns of land-use change have lead conservationists to increasingly rely on human-dominated landscapes for biodiversity conservation. However, the effectiveness of one such landscape, military training areas (MTAs), for conservation has rarely been evaluated. MTAs may harbor rare habitat types, but these sites are also often heavily impacted and may not be managed primarily for conservation. We sought to assess whether an MTA could serve as an effective site for conservation of extremely rare butterfly, the eastern regal fritillary (Speyeria idalia idalia) on Fort Indiantown Gap National Guard Training Center in southeastern Pennsylvania. Eighteen years of count data exist for this species. Reliable analysis of these data, however, has been complicated by typical challenges of long-term wildlife monitoring data (non-normal error distributions, non-independence of sampling, non-linearity in population pattern over time, and inter-observer differences), as well as by the natural history of these butterflies (differences by season and by sex in detectability, excessive zero counts), and particular challenges inherent in monitoring on an MTA (uneven sampling). We therefore used a novel approach to model butterfly population patterns, incorporating a multi-step modelling process, the use of zero-inflated generalized additive mixed models in a Bayesian framework, and graphical rendering of population patterns.
Results/Conclusions
Our results provide the first comprehensive analysis of population trajectories for S. i. idalia, and suggest that after a long period of decline, populations have increased and – more recently – stabilized. Temporal concordance of this increase with the onset of prescribed burning with aerial ignition and logging, suggest the importance of active management efforts for conservation of this subspecies, and for biodiversity more generally within MTAs. This study supports the idea that an MTA not only can host a globally threatened species, but as long as this and similar human modified areas are effectively managed they can promote the coexistence of multiple land uses, in a successful and sustainable manner.