Environmental variables associated with the distribution and occupancy of habitat specialist tadpoles in naturally acidic, oligotrophic waterbodies

Abstract

Environmental factors play an integral role, either directly or indirectly, in structuring faunal assemblages. Water chemistry, predation, hydroperiod and competition influence tadpole assemblages within waterbodies. We surveyed aquatic predators, habitat refugia, water height and water chemistry variables (pH, salinity and turbidity) at 37 waterbodies over an intensive 22‐day field survey to determine which environmental factors influence the relative abundance and occupancy of two habitat specialist anuran tadpole species in naturally acidic, oligotrophic waterbodies within eastern Australian wallum communities. The majority of tadpoles found were of Litoria olongburensis (wallum sedge frog) and Crinia tinnula (wallum froglet) species, both habitat specialists that are associated with wallum waterbodies and listed as Vulnerable under the IUCN Red List. Tadpoles of two other species (Litoria fallax (eastern sedge frog), and Litoria cooloolensis (cooloola sedge frog)) were recorded from two waterbodies. Tadpoles of Litoria gracilenta (graceful treefrog) were recorded from one waterbody. Relative abundance and occupancy of L. olongburensis tadpoles were associated with pH and water depth. Additionally, L. olongburensis tadpole relative abundance was negatively associated with turbidity. Waterbody occupancy by C. tinnula tadpoles was negatively associated with predatory fish and water depth and positively associated with turbidity. Variables associated with relative abundance of C. tinnula tadpoles were inconclusive and further survey work is required to identify these environmental factors. Our results show that the ecology of specialist and non‐specialist tadpole species associated with ‘unique’ (e.g. wallum) waterbodies is complex and species specific, with specialist species likely dominating unique habitats.

Determining environmental limits of threatened species: the example of the wallum sedgefrog Litoria olongburensis

“…We previously reported a unimodal response to pH for relative abundance of wallum sedgefrog tadpoles, which were also sampled during surveys for the present study (Simpkins et al. ). Our modeling results herein indicate a unimodal response for adults, as well, indicating existence of both lower and upper limits along the pH gradient.…”

“…Water pH, salinity, temperature, turbidity, and depth were measured as described by Simpkins et al. (). Upright sedge cover was measured as described by Shuker and Hero ().…”

“…Simpkins et al. () provided quantitative evidence that the abundance of wallum sedgefrog tadpoles has a unimodal relationship with both pH and water depth (used as a proxy for hydroperiod). The limits of the species’ ecological niche in relation to these environmental variables, or any others, have not yet been determined.…”

“…Also, wallum sedgefrogs are thought to breed primarily in ephemeral or semi-permanent waters, rather than permanent waters (Ingram and Corben 1975, Ehmann 1997, Lewis and Goldingay 2005, Hines and Meyer 2011. Simpkins et al (2014) provided quantitative evidence that the abundance of wallum sedgefrog tadpoles has a unimodal relationship with both pH and water depth (used as a proxy for hydroperiod). The limits of the species' ecological niche in relation to these environmental variables, or any others, have not yet been determined.…”

Calling phenology and detectability of a threatened amphibian (Litoria olongburensis) in ephemeral wetlands varies along a latitudinal cline: Implications for management

“…Males call in most months of the year but are likely to display seasonality in calling intensity and activity (Hines & Meyer 2011). They breed in wetlands that periodically dry out (Lewis & Goldingay 2005;Shuker & Hero 2012;Simpkins et al 2013), which are strongly influenced by the timing and amount of spring and summer rainfall (Griffith et al 2008;Lowe et al 2015). The risk of reproductive failure for L. olongburensis depends on both the delay or lack of annual rainfall and the length of hydroperiod (Lowe et al 2015).…”