Endangered anurans in a novel forest in the highlands of Sri Lanka

Abstract

Context Lands without agricultural or urban use embedded within agricultural and urban regions now account for ~35% of Earth’s terrestrial extent. Although created by human disturbances, these ‘novel ecosystems’, usually poor in native flora and often dominated by alien species, do not require human intervention for their maintenance. Given their large and increasing area, however, their ability to support native – and especially threatened – faunas warrants investigation. With 20 species already extinct and 47 of its 91 extant species assessed as Endangered or Critically Endangered, Sri Lanka’s amphibian fauna is in trouble. The 18 anurans (12 of these Endangered) occurring above 1500 m in the island’s central mountains are at particular risk from drastic declines in the extent and quality of habitat. Habitat restoration, however, is retarded by successional vegetation being arrested at least in the decadal time-frame by alien invasive species, creating a ‘novel ecosystem’. Aim To investigate whether such an ecosystem is able to support native anurans with a species richness and abundance comparable to that of neighbouring tropical montane cloud forest. Methods We surveyed 110 transects (each 20 m × 2 m) across three neighbouring locations covering three microhabitat-types, and recorded 552 specimens. One-way analyses of variance and post hoc, pair-wise Tukey’s tests were performed to test for differences in species richness and abundance among the three microhabitat types. Key result Of the 15 anuran species occurring in the neighbouring primary forest, 12 (eight of them Endangered) had established populations in the novel ecosystem (a former tea plantation), with abundances comparable to (or in some cases exceeding) those in primary forest. Conclusion Even young secondary forest dominated by alien plant species, in which native vegetation is almost wholly absent, can provide adequate habitat for most threatened highland anurans in Sri Lanka. Implications (1) Even if florally poor and dominated by alien species, novel ecosystems may present potential conservation opportunities for previously threatened faunas. (2) Threatened anurans exclusively dependent on primary forest and unable to utilise secondary-growth forest should receive greater conservation attention and be prioritised for in situ conservation measures. (3) Given their large and increasing extent globally, novel ecosystems should be considered as part of the area of occupancy of species able to complete their life cycles in them when assessed for conservation purposes, rather than being arbitrarily discarded as ‘degraded’.