Evolutionary refugia and ecological refuges: key concepts for conserving Australian arid zone freshwater biodiversity under climate change

Abstract

Refugia have been suggested as priority sites for conservation under climate change because of their ability to facilitate survival of biota under adverse conditions. Here, we review the likely role of refugial habitats in conserving freshwater biota in arid Australian aquatic systems where the major long-term climatic influence has been aridification. We introduce a conceptual model that characterizes evolutionary refugia and ecological refuges based on our review of the attributes of aquatic habitats and freshwater taxa (fishes and aquatic invertebrates) in arid Australia. We also identify methods of recognizing likely future refugia and approaches to assessing the vulnerability of arid-adapted freshwater biota to a warming and drying climate. Evolutionary refugia in arid areas are characterized as permanent, groundwater-dependent habitats (subterranean aquifers and springs) supporting vicariant relicts and short-range endemics. Ecological refuges can vary across space and time, depending on the dispersal abilities of aquatic taxa and the geographical proximity and hydrological connectivity of aquatic habitats. The most important are the perennial waterbodies (both groundwater and surface water fed) that support obligate aquatic organisms. These species will persist where suitable habitats are available and dispersal pathways are maintained. For very mobile species (invertebrates with an aerial dispersal phase) evolutionary refugia may also act as ecological refuges. Evolutionary refugia are likely future refugia because their water source (groundwater) is decoupled from local precipitation. However, their biota is extremely vulnerable to changes in local conditions because population extinction risks cannot be abated by the dispersal of individuals from other sites. Conservation planning must incorporate a high level of protection for aquifers that support refugial sites. Ecological refuges are vulnerable to changes in regional climate because they have little thermal or hydrological buffering. Accordingly, conservation planning must focus on maintaining meta-population processes, especially through dynamic connectivity between aquatic habitats at a landscape scale.

Australian spiny mountain crayfish and their temnocephalan ectosymbionts: an ancient association on the edge of coextinction?

“…From approximately 90 Ma, uplift of the great dividing range (GDR) [28] established the main river basins seen today (figure 1) [29]. During this period, Australia drifted northwards by approximately 308 (from 43 to 108 S) [29]. This was accompanied by broad climate warming and considerable drying, with a contraction of high rainfall biomes [29][30][31].…”

“…Since then, Australia has experienced major environmental change associated with the break-up of Gondwana (which began around 165 Ma) [22,27]. From approximately 90 Ma, uplift of the great dividing range (GDR) [28] established the main river basins seen today (figure 1) [29]. During this period, Australia drifted northwards by approximately 308 (from 43 to 108 S) [29].…”

“…During this period, Australia drifted northwards by approximately 308 (from 43 to 108 S) [29]. This was accompanied by broad climate warming and considerable drying, with a contraction of high rainfall biomes [29][30][31]. Consequently, it has been suggested that modern Euastacus (particularly the high-altitude species of northern Queensland) represent relicts of a cooler past climate [32,33].…”

Humans, water, and the colonization of Australia

“…Although it is possible that springs in local areas will activate or deactivate over time and that billabongs and other small water sources in bedrock (gnammas, rockholes) will form and disappear over time, the areas where such features have been located in the past can be assumed to be relatively constant, because they require particular lithologies, hydrogeological environments, and/or geomorphic settings. Hence their modern distribution is likely broadly comparable to their distribution in the past, with many such locations being important refugia as a result of their longterm stability (56)(57)(58). In the context of early human dispersal, small isolated water points (identified from topographic sheets) are likely to have been less significant than areas connected during times of inundation (identified by the WOfS data), because of the risk associated with striking out into an unknown area across an intervening landscape with no known water points.…”

Detecting microrefugia in semi-arid landscapes from remotely sensed vegetation dynamics

“…However, axes such as moisture availability (hydrologic refugia; Davis et al, 2013;McLaughlin et al, 2017) or disturbance (eg, fire refugia; Ouarmim et al, 2014;Wilkin et al, 2016) are equally important (Reside et al, 2014). In addition, refugia can operate over multiple time frames, determined by their size and permanence (ie, the degree to which they are decoupled from regional conditions).…”