Mammalian and avian diversity in a coastal nature reserve and an adjacent eco-estate

Ross, Michael

Mammalian and avian diversity in a coastal nature reserve and an adjacent eco-estate

Master Thesis

2022

Abstract

The burgeoning human population is placing increasing pressure on natural resources, including undeveloped land, for a variety of human activities including residential housing. Despite making up only a small percentage (5.4 %) of transformed land, urban areas have had a disproportionate impact on biodiversity with many cities having been founded in biodiversity hotspots at the confluence of marine, freshwater and terrestrial ecosystems. A growing trend worldwide and particularly in countries with a large wealth gap is the development of low density private residential estates. Although primarily conceived to improve home security, private estates are nevertheless regarded as a form of geographical escapism, and they are increasingly being marketed as eco- and lifestyle estates. While no formal definition of an eco-estate exists nor what ecological criteria must be satisfied to qualify for the status of an “ecological estate,” increasingly such estates make bold claims concerning their contributions to the conservation of native flora and fauna. Currently, little is known about the impacts of eco-estates on the ecology and wildlife of an area, particularly when compared to natural land. To date, most research on estates has focused on comparing their impact with transformed, agricultural or even urban land uses. In this study I compare select elements of the fauna within a golfing eco-estate (Atlantic Beach Estate), located 25 km north of Cape Town to the neighbouring Blaauwberg Nature Reserve, from which the estate was originally cleaved. I used live trapping, camera trapping and point counts for small mammals, medium/large mammals and birds respectively to compare the fauna in both the estate and reserve. For birds I was able to include a before and after comparison with a similar study in the early phases of the estate's development. All fieldwork was conducted between September and November 2019. Small mammal diversity was similar within the estate and the reserve, but the former included an exotic invasive (the house rat (Rattus rattus)) while the latter supported the vulnerable white-tailed rat (Mystromys albicaudatus). Medium sized mammal species composition varied significantly between the estate and reserve with the latter having more native species and the estate having three domestic species in addition to an introduced, extralimital wild species, the springbok (Antidorcas marsupialis). Bird communities were similar, with marked overlap in species between the two land uses. The addition of permanent water and private gardens with both native and non-native flora has increased both the niche breadth and food availability within the estate which was reflected in a higher avian diversity than in the neighbouring, more homogenous, reserve. In addition to supporting almost all the species found in the reserve, the estate was able to support multiple fynbos-endemic species not found in the nature reserve, as well as species closely associated with water. The presence of the eco-estate does not appear to have negatively impacted the bird community as the additional resources provided by the estate allow both urban exploiters and urban tolerators/avoiders to persist. In summary the estate has adversely impacted medium sized mammals more than both small mammals and birds with the latter taxon arguably benefiting from the increased habitat heterogeneity. Improving medium sized mammal richness would require increasing the permeability of the estate boundary but this will compromise both the safety of residents from external human threats and mammals within the reserve from domestic animals originating from the estate. Restricting domestic animals to private property, eliminating exotic species, improving connectivity between patches of natural habitat and naturalizing the edges of the golf course are all attainable goals that may improve small mammal and bird communities within the estate. However medium and large mammals are seldom compatible with human habitation and are thus likely to be the faunal component most adversely impacted by eco-estates with their limited size and impermeable edges. Ultimately while eco-estates may offer habitat for some species, they are not uniformly suitable for all species, and particular attention must be given to characteristics of prevailing species which might preclude them from an estate before estate construction. Given the increasing popularity of eco-estates and increased pressure on wildlife these are important findings which can help improve conditions for wildlife on current eco-estates and help facilitate site selection for any future eco-estate construction.

Keywords

biological sciences

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