Abstract
The Azorean islands have been historically affected by human activities, mainly due to the combined effects of habitat degradation and fragmentation, and the introduction of exotic species. We here aim to analyze the role of environmental characteristics and spatial descriptors in supporting regional biodiversity of macroinvertebrates by considering natural ponds and artificial tanks. After the monthly variation of macroinvertebrate assemblages was assessed in three temporary and two permanent ponds in the Azorean island of Terceira during a complete inundation-desiccation annual cycle, the assemblage differences of 12 ponds (three temporary and nine permanent ponds) and 8 closely-located artificial tanks were analyzed across a range of landscape disturbances. Macroinvertebrate assemblages were found to differ according to hydroperiod and sampled months. Although the former explained the highest variance, macroinvertebrate differentiation by hydroperiod was also dependent on the study month. Our results also revealed a consistent monthly pattern of species replacement. However, the contribution of nestedness to the macroinvertebrate β-diversity was notable when temporary ponds were close to desiccation, probably indicating a deterministic loss of species due to the impoverished water conditions of the ponds facing desiccation. When the macroinvertebrate assemblages were analyzed in relation to physico-chemical variations and spatial descriptors, the artificial tanks were not clearly segregated from the natural ponds, and only differentiated by pH differences. In contrast, those natural ponds exhibiting high concentrations of total phosphorous (likely signs of anthropization) also discriminated the ordination of ponds in a distance-based redundancy analysis, and showed impoverished assemblages in comparison with well-preserved ponds. The macroinvertebrate assemblages of the natural ponds showed a significant spatial pattern, but this spatial influence was not significant when tanks and ponds were considered together. Our results suggest that tanks may act as possible reservoirs of biodiversity during the desiccation period of temporary ponds, but are unable to establish successful populations. These fishless permanent tanks can complement the conservation of a biodiversity that is largely maintained by the pristine high-altitude natural ponds. The establishment of a guideline for conservation management that also considers the artificial tanks is necessary to benefit the local and regional Azorean macroinvertebrate diversity.
Highlights
Freshwater ecosystems are currently highly vulnerable to external perturbations associated with anthropogenic changes, mainly due to the introduction of exotic species, landscape transformations and climate change (Sala et al, 2000; Pyšek et al, 2010)
Temporary ponds had the highest occurrence of endemic species, and exhibited the highest proportion of endemic individuals
Our results suggest that the studied artificial tanks maintain good water quality and are suitable for macroinvertebrate species, increasing the heterogeneity of habitats as permanent waterbodies in the peak of the hydroperiod gradient
Summary
Freshwater ecosystems are currently highly vulnerable to external perturbations associated with anthropogenic changes, mainly due to the introduction of exotic species, landscape transformations and climate change (Sala et al, 2000; Pyšek et al, 2010). 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, 2018, 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). The particular environmental conditions that favor or deplete biodiversity in artificial ponds across different land-uses, and their positive or negative contribution to biodiversity in a natural pond network remain quite unexplored
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