Alien and native birds in South Africa: patterns, processes and conservation

Abstract

The spatial distribution of alien species richness often correlates positively with native species richness, and reflects the role of human density and activity, and primary productivity and habitat heterogeneity, in facilitating the establishment and spread of alien species. Here, we investigate the relationship between the spatial distribution of alien bird species, human density, and anthropogenic and natural environmental conditions. Next, we examined the relationship between the spatial distribution of alien bird species and native bird species richness. We examined alien species richness as a response variable, using correlative analyses that take spatial autocorrelation into account. Further, each alien bird species was examined as a response variable, using logistic regression procedures based on binary presence-absence data. A combination of human density and natural habitat heterogeneity best explained the spatial distribution of alien species richness. This contrasts with the results for individual alien species and with previous studies on other non-native taxa showing the importance of primary productivity and anthropogenic habitat modification as explanatory variables. In general, native species richness is an important correlate of the spatial distribution of alien species richness and individual alien species, with alien species being more similar to common species than to rare species.

Founder populations and the current status of exotic parrots in South Africa

“…Most parrots are cavity nesters (although some parrots may nest in buildings), so their role in limiting the breeding success of competitors is immediately questioned (Czajka et al 2011). However, given the already large degree of environmental change and biotic homogenisation in urban areas by humans, one questions the validity of recognising such species as threats to an already transformed biota (Blair 1996;Hugo and van Rensburg 2009). For example, the avian community of urban Gauteng is already vastly different to what it was c. 100 years ago.…”

Are environmental transitions more prone to biological invasions?

“…Firstly, boundaries between ecoregions are areas of sharp transition with especially high spatial and temporal heterogeneity and often show lower spatio-temporal stability and predictability compared to the core of an ecoregion (Killeen & Sol orzano, 2008). Increased heterogeneity, both spatially and temporally, is well known to be positively correlated with species richness for many taxa, spatial scales and regions (Rosenzweig, 1995;van Rensburg et al, 2002;Pino et al, 2005;Thuiller et al, 2006;Hugo & van Rensburg, 2009;Levanoni et al, 2011) and is also consistent with the general theory of invasibility related to fluctuating resources proposed by Davis Table 2 Distance to the nearest ecotone (boundary between vegetation communities), variation in energy (minimum temperature) and productivity (NDVI) were analysed as predictors of invasive alien species richness. We represent here, for each multiple regression model, the coefficient of determination indicating the explanatory power of all relevant predictors in that model (full model r 2 ), a partial coefficient of determination indicating the explanatory power of only the ecotone distance variable, and the F ratio, significance level and the sign of the slope (positive or negative relationship) of each predictor variable.…”

Terrestrial Vertebrate Invasions in South Africa

“…Physiological experiments on caged South African parakeets suggest that these birds are tolerant of a wide range of ambient, especially low temperatures, and are therefore equipped to cope with a variety of climatic situations in the country (Thabethe et al 2013). However, occurrence of the Rose-ringed Parakeet in South Africa is currently best predicted by human density (Hugo and van Rensburg 2009). Despite their known impacts as an invasive species, these birds are still popular as cage birds in South Africa, and 55 of 78 properties issued with notices under the Regulations were for Rose-ringed Parakeets, with the majority of these being for traders (van Wilgen and Wilson 2018).…”