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Environmental Biology

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Browsing Environmental Biology by Author "Mackey, Robin L."

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    The effect of wastewater works on foraging behaviour and metal content of Neoromicia nana (Family : Vespertilionidae)
    (2011) Naidoo, Samantha.; Schoeman, Marthinus Cornelius.; Vosloo, Dalene.; Mackey, Robin L.
    Anthropogenic disturbance from urbanization has introduced a range of contaminants into freshwater ecosystems. Wastewater Treatment Works (WWTW) in particular, deposit effluent with high metal concentrations directly into rivers. These pollutants may affect river biota directly or through modifications to habitat and prey. Therefore, the impact of metal pollution through a food chain should be evident in high trophic level predators such as Neoromicia nana. N. nana is a small, insect-eating bat that occurs in forest and riparian habitats in Africa. Most importantly, it is an urban exploiter, i.e. a species that takes advantage of anthropogenic food and habitat resources. I investigated the foraging behaviour and metal content of N. nana at wastewater-polluted sites (WWTW sludge tanks and sites downstream of wastewater discharge into the rivers) and unpolluted sites (sites upstream of wastewater discharge) at three urban rivers in Durban, South Africa, during winter and summer. To assess water quality, I determined cadmium, copper, chromium, iron, nickel, zinc and lead concentrations using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). To investigate the foraging behaviour of N. nana, I quantified relative N. nana abundance, and feeding activity from recorded echolocation calls. Using ICP-OES, I quantified metal concentrations in three tissues (liver, kidney and muscle). My results show that concentrations of most metals were generally lowest upstream, intermediate at downstream sites and highest at the tanks. The relative abundance and feeding activity of N. nana were significantly higher at wastewater-polluted sites than at upstream sites, despite there being significantly more insect orders upstream. However, pollution-tolerant Chironomidae (Diptera), were significantly more abundant at wastewater-polluted sites. Indeed, at wastewater-polluted sites, Diptera represented the highest percentage of insects in the diet of N. nana. Essential metals (copper, zinc and iron) were detected in all tissue samples of N. nana. In contrast, the toxic metals cadmium, chromium and nickel were present in tissue of bats only at wastewater-polluted sites (except one upstream occurrence of cadmium). This suggests that these metals may accumulate in tissue through the ingestion of pollutant-exposed prey. Thus, metal pollution from WWTWs affects not only water quality of rivers, but also the diversity of resident aquatic insects and ultimately the ecology of N. nana populations, which may pose serious long-term health risks for these top predators.
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    The relative influence of local and landscape processes on the structure of insectivorous bat ensembles in urban nature reserves.
    (2012) Moonsamy, Shivani.; Schoeman, Marthinus Cornelius.; Mackey, Robin L.
    Urbanization is arguably the most damaging and rapidly expanding threat to biodiversity. The process of urbanization results in the fragmentation of natural habitat into patches that are disjunct and isolated from one another. Biogeography theory predicts that landscape processes, including fragment size and isolation, should predominate in species assembly. However, these predictions have not been tested on African bats in urban landscapes. Bats are important models for urban studies because they comprise more than a fifth of all mammals, and play vital roles as primary, secondary and tertiary consumers that support human-dominated ecosystems. Furthermore, there is evidence that local, biotic processes specifically competition and prey defences are important determinants of species composition patterns. In this study, I investigated the relative influence of local and landscape processes on the species composition patterns of insectivorous bat ensembles in Durban. Using active capture methods and passive monitoring, I sampled the insectivorous bat ensembles of eight nature reserves in Durban between 2008 and 2010. I used multivariate analyses to test predictions from biogeographic and climate hypotheses, and I used null model analyses to test predictions from competition and nestedness hypotheses to determine whether the bat richness patterns were significantly different from patterns expected by chance. Species richness estimators indicated that species inventories for ensembles were fairly complete (i.e. estimated species richness was not much larger than observed species richness). Multiple regression analyses showed that there was a significant parabolic relationship between species evenness and daily maximum temperature, and there was a significant negative relationship between relative activity and reserve shape. However, I found no evidence that competition influenced species composition patterns. Conversely, I found support for the nestedness hypothesis: species in species-poor ensembles were subsets of species in species-rich ensembles. Spearman rank correlation indicated that the degree of nestedness was significantly correlated with maximum temperature. My results suggest that in urban landscapes, abiotic processes operating at the landscape scale may be more important determinants of composition patterns of insectivorous bat species than biotic factors operating at a local scale. Furthermore, bat species that forage in cluttered habitats may not be able to persist in urban landscapes.