The effect of habitat disturbance on common Lepidoptera in the New Jersey Pinelands

Background/Question/Methods   Anthropogenic impacts have been implicated in the worldwide decline of lepidopteran species. Although there is a growing concern that both rare and common species are being impacted, little research has been conducted on the effect that human activities are having on common species. We report the preliminary results (2008-2009) for an ongoing study being conducted at the Warren Grove Gunnery Range (WGR) on the impact of military habitat disturbance on the local population of common Lepidoptera. The WGR (3810 hectares) is an active air-to-ground gunnery range located in the heart of the New Jersey Pinelands. The landscape at WGR is a mosaic of intact upland pine-oak forests, wetlands, and disturbed habitats. Baseline data on species composition, habitat use, and abundance will be important for detecting shifts in population trends (stable, increasing, or declining) and for developing conservation strategies for common species that are in decline. We conducted random and timed searches (sensu Pollard Walks) along permanent transects to compare differences between disturbed and undisturbed habitats. We calculated species-encounter-rate (SER = #species/minute sampling time) and individual-encounter-rate (IER = #individuals/minute sampling time) to elucidate differences among habitats for species richness, composition, and abundance.

Results/Conclusions   Habitat heterogeneity at WGR supports a diverse assemblage of common and rare Lepidoptera. Dry-grassland habitat in open disturbed fields within the target zone had the highest SER (0.15/min), followed by naturally disturbed pitch pine-lowland habitat (0.13/min) last burned in 2004, Atlantic-white cedar bog (SER = 0.11/min), and recently restored pitch pine habitat (SER = 0.06/min). Dry-grassland habitat (n=25) and pitch-pine lowland habitat (n=23) supported the greatest species richness. Atlantic-white cedar bog had the greatest IER (2.25/min), followed by dry-grassland habitat (1.07/min), disturbed pitch pine-lowland habitat (0.46/min), and restored pitch pine forest (0.14/min). Only two species occurred among the four habitat types. Atlantic-white cedar bog (n=9) supported the greatest number of unique species, followed by dry grassland (n=8), restored pitch pine forest (n=7), and pitch pine-lowland (n=1) habitats. These data suggest that disturbed habitats with early-successional host plants support a wide suite of species. In contrast, the least disturbed habitat (i.e., Atlantic-white cedar bog) supported the greatest number of unique species. The observed species composition and habitat occurrence at WGR was facilitated by a patchwork of large tracts of relatively undisturbed habitat interspersed with small pockets of disturbed habitat where the disturbance regime has maintained ideal conditions for disturbance-dependent species.