Assessing Natural Variation as a Baseline for Biodiversity Monitoring: The Case of an East Mediterranean Canyon

Accurately assessing the natural variation in biodiversity is crucial as a baseline for monitoring trends and attributing them to natural or anthropogenic drivers. To assess this baseline, we estimated the species richness, composition and abundance of plants, beetles and ants in Evolution Canyon II (Israel), a protected reserve in the Eastern Mediterranean that is known both for its heterogeneity and for faster-than-average climate change. Consecutive sampling over 24 months in three divergent microhabitats of the canyon (south-facing xeric and north-facing mesic slopes and the valley bottom) during 2019–2021 was conducted using the same methods employed at the same site during 1998–2000, enabling us to also study seasonal and inter-annual variation. Altogether, 459 beetle species, 349 plant species and 47 ant species were found. These taxa exhibit substantial and persistent divergence between canyon slopes. Despite substantial species turnover rates between periods in all the taxa, almost no change was found regarding the biogeographical origins of plant and beetle species composition. In addition, species richness differences between microhabitats persisted between study periods, and year-round sampling revealed many dominant winter-peaking beetle species. These findings reflect the importance of thoroughly surveying diverse taxa, microhabitats, seasons and annual weather patterns when characterizing the natural baseline of a monitoring program.