Biodiversity conservation across taxa and landscapes requires many small as well as single large habitat fragments

Abstract

Agricultural intensification has been shown to reduce biodiversity through processes such as habitat degradation and fragmentation. We tested whether several small or single large habitat fragments (re-visiting the 'single large or several small' debate) support more species across a wide range of taxonomic groups (plants, leafhoppers, true bugs, snails). Our study comprised 14 small (<1 ha) and 14 large (1.5-8 ha) fragments of calcareous grassland in Central Germany along orthogonal gradients of landscape complexity and habitat connectivity. Each taxon was sampled on six plots per fragment. Across taxa, species richness did not differ between large and small fragments, whereas species-area accumulation curves showed that both overall and specialist species richness was much higher on several small fragments of calcareous grassland than on few large fragments. On average, 85% of the overall species richness was recorded on all small fragments taken together (4.6 ha), whereas the two largest ones (15.1 ha) only accounted for 37% of the species. This could be due to the greater geographic extent covered by many small fragments. However, community composition differed strongly between large and small fragments, and some of the rarest specialist species appeared to be confined to large fragments. The surrounding landscape did not show any consistent effects on species richness and community composition. Our results show that both single large and many small fragments are needed to promote landscape-wide biodiversity across taxa. We therefore question the focus on large fragments only and call for a new diversified habitat fragmentation strategy for biodiversity conservation.

An experimental test of the habitat‐amount hypothesis for saproxylic beetles in a forested region

“…, Rösch et al. ). These studies regularly attribute this pattern to higher habitat heterogeneity represented by several small patches than a single large patch.…”

Delayed mowing promotes planthoppers, leafhoppers and spiders in extensively managed meadows

“…As some subgroups had lower abundances in R‐ (at least in the cut area) than C‐meadows, this research confirms that reinstating spatio‐temporal management heterogeneity within agricultural matrices is key to the preservation and restoration of farmland biological diversity (Benton et al ., ; Batáry et al ., ; Diacon‐Bolli et al ., ; Rösch et al ., ). These two readily implementable options (delaying mowing or leaving uncut refuges) would probably benefit from being applied in concert, in the form of two alternative, complementary measures to be incorporated into future grassland AES, though the benefits of such a conjunction still need to be demonstrated.…”

Fragmentation of hardwood floodplain forests — how does it affect species composition?

“…No relationship between plant species richness and fragment size was found in grasslands (Rösch et al 2015). A time lag exists in plant communities' response to changes in habi- tat configuration, as demonstrated by Lindborg and Eriksson (2004), and this may also contribute to the inconsistent species-area effects observed in Santos et al' s (2007) fragments.…”

“…In contrast to previous studies (e.g., Santos et al 2007, Wu et al 2013, Rösch 2015, the natural species composition is defined according to species groups obtained using phytocoenological methods. The aim of the study was to test the hypothesis that higher fragmentation influenced negatively the diversity of forest species groups and positively the occurrence of aliens.…”