Aquatic insects decline in abundance and occupy low‐quality artificial habitats to survive hydrological droughts

Abstract

Hydrological extremes have negative impacts on natural, agricultural, and urban landscapes and place substantial ecological pressure on freshwater habitats. However, the role of artificial freshwater habitats during hydrological drought is poorly understood. Insects make up much of total aquatic fauna and lend themselves to understanding how drought impacts freshwater ecosystems. Using the Greater Cape Floristic Region as an example of a drought‐prone area, we determined the effects of a severe drought on a subset of insects occupying lentic habitats in terms of their species richness, diversity, and assemblage composition. Here, we: (1) calculated the percentage change in average precipitation between a record dry season and the last consistently wet decade; (2) identified the environmental variables driving aquatic insect species richness, diversity and composition; (3) identified the environmental differences between natural ponds and artificial reservoirs; (4) determined whether artificial reservoirs act as suitable habitats for focal taxa during drought; and (5) compared these results to other, pre‐drought studies. Environmental variables related to water chemistry and physical characteristics were drivers of species richness, diversity, and composition, yet vegetation cover remained a major driver. In terms of marginal vegetation cover, most artificial reservoirs did not resemble natural ponds, yet overall 38.4% of sampled aquatic insect species were shared between natural ponds and artificial reservoirs. We found some rare endemic species in artificial reservoirs that had never before been recorded in this habitat during wet years. When our drought findings were compared to earlier, wet years, species richness did not change significantly, although abundance was much lower during the drought year. We postulate that historically, these aquatic insects, which have been through many ecological filters such as drought, must have sought low‐quality habitats to survive water stress periods. Artificial reservoirs, being novel landscape features, cannot fully replace natural ponds, but enable some aquatic insects to survive drought. Artificial reservoirs can be attractive habitats to aquatic insects when they resemble natural ponds, with specific reference to their marginal vegetation characteristics.

Protected and un-protected urban wetlands have similar aquatic macroinvertebrate communities: A case study from the Cape Flats Sand Fynbos region of southern Africa

“…The Western Cape province of South Africa, where the current study was conducted, experienced its worst drought in over a century between the years 2015-2017 [53]. Recent analysis of the responses of aquatic biodiversity demonstrated some unusual patterns, with some rare, endemic species that were not found on pre-drought sampling and are now occupying in low quality artificial habitats [54]. Drought could severely impact the community structure of temporary wetlands in the wet phase, as duration of the dry/wet phase changeover within temporary wetlands will influence which species emerge in the wet phase.…”

Effects of both climate change and human water demand on a highly threatened damselfly

“…The creation of an artificial ditch system that could be used both for irrigation and refuge for the lotic fauna in case of an extreme drought could attenuate the impact of drought on lotic ecosystems 67 . In South Africa, some Cape endemic species occupy artificial reservoirs during severe drought events and use them as refuges until the favorable conditions return in their reproductive areas 68 . This escape behavior is typical of drought-adapted lotic endemics that are dependent on perennial rivers and streams to reproduce and maintain viable populations.…”

Biodiversity Patterns of Macroinvertebrate Assemblages in Natural and Artificial Lentic Waters on an Oceanic Island

“…In contrast to the general negative role of human disturbance in shaping biodiversity, artificial ponds or tanks associated with agricultural systems have sometimes demonstrated that they are able to sustain biodiversity (Abellán et al, 2006;Declerck et al, 2006;Céréghino et al, 2008;Thiere et al, 2009). These humanmade ponds usually have different environmental characteristics in comparison with natural ponds (e.g., Hill et al, 2016, but see Deacon et al, 2018Deacon et al, , 2019 for similar chemical properties), given that these artificial systems usually have concrete sides and reduced vegetation cover, and possibly higher contaminant inputs compared to natural ponds (Hassall, 2014). Artificial ponds usually show reduced freshwater biodiversity, can support the occurrence of exotic species and may act as possible ecological traps (Oertli and Parris, 2019).…”