Simultaneous effect of habitat remnancy, exotic species, and anthropogenic disturbance on orchid diversity in South Australia

Orchids are potentially useful as ecological indicators because of their sensitivity to habitat fragmentation and anthropogenic disturbance. While many studies explore the effect of single factors on orchid diversity, few investigate how the extent, configuration, and condition of surrounding habitat affect whole orchid communities. Here, we unravel the effect of biological invasions, anthropogenic disturbance (i.e., grazing pressure, ecological condition), and habitat fragmentation on an Australian orchid community. We sampled 39 plots across nine sites in the Mount Lofty Ranges, Australia. We recorded the number of orchid species and number of individuals per species in mid-winter, early-spring, and late-spring to account for the effect of season on species visibility, with 115 surveys in total. We ranked grazing intensity and ecological condition, and estimated cover of exotic species. We analyzed the response of richness and diversity through generalized linear mixed models, and differences in species composition through non-metric multidimensional scaling. Habitat configuration in the surrounding landscape had different effects at increasing radii, explaining 29%-87% of variance. Patch-level orchid diversity was positively correlated with habitat edges in the immediate area, and with habitat cohesion at medium scales, whereas diversity was negatively correlated with increasing mean patch habitat area across larger surrounding areas. Orchids co-existed with exotic species but were negatively affected once exotic cover exceeded 20%. Species composition was correlated with exotic cover. Our findings reveal a complex relationship between orchid communities and their surrounding environments suggesting orchids benefit from a somewhat disturbed environment at patch and landscape scales. These idiosyncratic responses suggest orchid diversity may be unreliable as early-warning indicators of habitat disturbance.

Automated summary

Orchids are sensitive to habitat fragmentation and anthropogenic disturbance, making them potentially useful as ecological indicators. This study explores the effect of biological invasions, disturbance, and habitat fragmentation on an Australian orchid community. The results reveal a complex relationship between orchids and their surrounding environments, with different effects observed at different spatial scales. Orchids benefit from a somewhat disturbed environment but are negatively affected once exotic cover exceeds 20%. The reliability of orchid diversity as early-warning indicators of habitat disturbance may be limited.