Geographic variation in the phenotypes of two sibling horseshoe bats Rhinolophus simulator and R.swinnyi

The study of geographic variation and its causes in the phenotypes of animals elucidates how evolutionary processes generate biodiversity. This thesis attempts to uncouple the relative contributions of adaptive and neutral mechanisms to population divergence in African horseshoe bats (genus Rhinolophus). The two species were sampled from their distributional ranges within southern Africa and several morphometric and echolocation parameters were taken. The relative contributions of adaptation and drift were first tested (Chapter 2) using the Lande's model. It was hypothesised that adaptation would predominate in the diversification of the two horseshoe bats owing to the flight-echolocation and diet-echolocation adaptive complexes that intricately tie these two species to environmental conditions. Selection was also hypothesised to be stronger in Rhinolophus swinnyi because it uses higher frequency sound which is more sensitive to atmospheric conditions. The hypotheses were tested using a combination of soft tissue parameters (Chapter 2) and hard tissue parameters (Chapter 3), i.e., 3D scanned skulls analysed using 3D geometric morphometrics. To reconstruct the selective forces, linear mixed-effects models were used to regress climatic variables against echolocation call signals (Chapter 4) based on two hypotheses, the Sensory Drive and the James' Rule as a guide. The Lande's model (Chapter 2 and 3) showed that drift had a minimal effect to the variation of body parameters and echolocation and that selection was stronger on echolocation than on morphometric parameters. Additionally selection was differentially exerted across different localities and between the two species, making the relative roles of selection and drift context specific. Climatic variables (mean annual temperature and relative humidity) were inversely related to the variation in echolocation signals (Chapter 4) within each species. Body size was unrelated to the observed variation, which provided evidence that echolocation signals did not vary as a result of the body size/climate relationship proposed by James' Rule. Bats rely on both flight and echolocation to survive and reproduce, systems that have to track local habitats closely to perform optimally. Hence selection plays a pivotal role in their diversification

Sensory drive mediated by climatic gradients partially explains divergence in acoustic signals in two horseshoe bat species, Rhinolophus swinnyi and Rhinolophus simulator

Geographic variation can be an indicator of still poorly understood evolutionary processes such as adaptation and drift. Sensory systems used in communication play a key role in mate choice and species recognition. Habitat-mediated (i.e. adaptive) differences in communication signals may therefore lead to diversification. We investigated geographic variation in echolocation calls of African horseshoe bats, Rhinolophus simulator and R . swinnyi in the context of two adaptive hypotheses: 1) James' Rule and 2) the Sensory Drive Hypothesis. According to James' Rule body-size should vary in response to relative humidity and temperature so that divergence in call frequency may therefore be the result of climate-mediated variation in body size because of the correlation between body size and call frequency. The Sensory Drive Hypothesis proposes that call frequency is a response to climate-induced differences in atmospheric attenuation and predicts that increases in atmospheric attenuation selects for calls of lower frequency. We measured the morphology and resting call frequency (RF) of 111 R . simulator and 126 R . swinnyi individuals across their distributional range to test the above hypotheses. Contrary to the prediction of James' Rule, divergence in body size could not explain the variation in RF. Instead, acoustic divergence in RF was best predicted by latitude, geography and climate-induced differences in atmospheric attenuation, as predicted by the Sensory Drive Hypothesis. Although variation in RF was strongly influenced by temperature and humidity, other climatic variables (associated with latitude and altitude) as well as drift (as suggested by a positive correlation between call variation and geographic distance, especially in R . simulator ) may also play an important role

Understanding arid-region waterbird community dynamics during lake dry-downs

The community dynamics of organisms that exhibit multi-scale responses to habitat change are poorly understood. We quantified changes in species diversity and the functional composition of a waterbird community over two iterations of a repeated transition, the annual drying-down of arid-region Lake Ngami, Botswana. We used our data to test three theoretical predictions: simplification of the bird community over time due to a reduction in habitat area and concurrent niche loss; large fluctuations in densities of mobile, opportunistic species; and high variance in predator and prey abundance. Despite temporal variance in species accumulation, we observed no obvious simplification and distinct but consistent groupings of abundance and composition across transitional stages. There were some rapid shifts in functional composition, such as loss of deepwater foragers; winners and losers also occurred within foraging guilds. We conclude that understanding community-level trends during transitional periods will require stronger theoretical frameworks that more effectively integrate unique species traits and functional groups. For conservation managers, our study offers a cautionary tale of the importance of understanding connectivity, trajectories of change, and the potential for large fluctuations in animal communities independent of management actions during periods of ecological transition

Predictive modelling plots showing how resting frequency (RF) in <i>Rhinolophus swinnyi</i> responded to environmental variation and sex.

<p>Abbreviations: e.g., PC (Altitude) represents a principle component generated by fixing mean-annual-temperature and relative humidity (rel.humidity) to their across-site-means whilst altitude is allowed to vary. The shaded areas and error bars represent 95% confidence limits. The final best model (with only variables shown significant after ANOVA on the best model) was used for the modelling.</p

Responses of an African wading bird community to resource pulses are related to foraging guild and food-web position

The immediate impacts of nutrient inputs on aquatic systems are well documented, but the ways in which resource pulses affect the wider food web of water-associated vertebrates remain obscure. 2.We monitored the wading bird community of Barberspan, a natural freshwater lake and Ramsar wetland in South Africa, before, during and after the addition of a pulse of nutrients in the form of a sewage overspill from an upstream processing facility. We counted waders at 13 points around the lake over 3years, every 2 months from March 2007 to March 2010, and sampled water quality during all counting periods from January 2008 to January 2010. 3.We used our data to test the hypothesis that wading birds that forage directly at lower trophic levels and/or on prey populations that have fast turnover rates, such as those of phytoplankton and invertebrates, will be more heavily influenced by nutrient addition than birds that forage on species with lower turnover rates and/or at higher trophic levels (such as frogs and fish). 4.During the sampling period Barberspan experienced a significant, nutrient-driven decline and subsequent recovery in dissolved oxygen and pH. This trend was mirrored by significant changes in the wading bird community. Partial Mantel tests and Canonical Correspondence Analysis (CCA) showed that the nutrient pulse had marked short-term, negative impacts on both the diversity and the abundance of medium-sized, shoreline foragers such as scolopacids (e.g. sandpipers). 5.Our analysis supports the proposal that both food-web position and the turnover rate of the prey population are strong influences on ecological responses to resource pulses. Analysis of time series of principal components that describe community composition suggested that recovery of the prey base was rapid and that the bird community was able to respond via immigration. These results must, of course, be considered provisional in the absence of replicated experimental data. 6.More generally, we interpret our results as suggesting that two different mechanisms act in different directions to determine the sensitivity of secondary and tertiary consumers to changes in their prey. First, for 'earlier' consumers (i.e. that forage lower in the food web), there are (on average) fewer generalist consumers and fewer stored nutrients in the intervening trophic levels. This increases the sensitivity of earlier consumer populations to changes in the composition of the primary consumer community. Second, the dynamics of prey populations lower in the food web tend to be faster, making recovery faster and serving to decrease the sensitivity of earlier consumers to perturbations. These dynamics may obscure the impacts of nutrient pulses in cases where additional analysis of system trajectories is not undertaken

Sampling sites within southern Africa from where <i>R</i>. <i>simulator</i> and <i>R</i>. <i>swinnyi</i> were caught.

<p>Abbreviations: CC = Chinhoyi, Zimbabwe; DM = Dambanzara, Zimbabwe; GKC = Gatkop Cave, South Africa; JET = Jiri Estate Triangle, Zimbabwe; KL = Kalenda, Zambia; KP = Kapatamukombe, Zimbabwe; LOB = Lobatse Estate, Botswana; MC = Mabura Cave, Zimbabwe; MM = Monaci Mine, Zimbabwe; MT = Matobo Hills, Zimbabwe; OD = Odzi German Shafts, Zimbabwe; PA = Pafuri, South Africa; SH = Shimabala, Zambia; and SUD = Sudwala, South Africa.</p

Predictive modelling plots showing how resting frequency (RF) in <i>Rhinolophus simulator</i> responded to environmental variation and sex.

<p>Abbreviations: e.g., PC (Altitude) represents a principle component generated by fixing mean-annual-temperature and relative humidity (rel.humidity) to their across-site-means while altitude was allowed to vary. The shaded areas and error bars represent 95% confidence limits. The final best model (only variables significant after ANOVA on the best model shown) was used for the modelling.</p

The ‘best’ model from forward-backward stepwise model selection on the global model of environmental variables, body size and sex against resting frequency for each of the two species, <i>Rhinolophus simulator</i> and <i>R</i>. <i>swinnyi</i>.

<p>Statistics are only presented for variables maintained in the best model.</p

Variation in environmental conditions (relative humidity; RH, mean annual temperature; AnnTemp and altitude; Alt) across sites from which <i>Rhinolophus simulator</i> and <i>R</i>. <i>swinnyi</i> were captured (based on principle component analysis).

<p>AnnTemp-PC1 and RH-PC2 accounted for 96% of the variation. Site abbreviations are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0148053#pone.0148053.g001" target="_blank">Fig 1</a>.</p

A study of moult-site fidelity in Egyptian geese, Alopochen aegyptiaca, in South Africa

Little is known about moult and moult-site fidelity of African waterfowl. Satellite  telemetry and uniquely engraved colour-rings were used to study moult-site fidelity of Egyptian geese marked at two sites in South Africa – Barberspan in the summer-rainfall region and Strandfontein in the winter-rainfall region. Twelve Egyptian geese were tagged with satellite GPS PTT transmitters while moulting at Barberspan and Strandfontein during 2008 and 2009, and a further 527 were colour-ringed between June 2007 and March 2009. Bi-monthly point counts of Egyptian geese and scans for colour-ringed birds were made at each study site from July 2007 until June 2010, resulting in 139 individually colour-ringed geese being re-sighted during the study period. We  explored Egyptian geese dispersal distances away from the study sites and modelled moult-site fidelity from colour-ring return rates corrected for survivorship, sampling period efficiency and colour-ring detectability estimates. There were 12% and 29.7% colour-ring return rates for geese ringed at Barberspan and Strandfontein, respectively. Four of five moulting birds tagged at Barberspan with satellite transmitters returned to Barberspan to moult the following year. Two of these same birds moulted at Barberspan in the third year while the other two moulted elsewhere. One out of seven Egyptian geese satellitetagged at   Strandfontein returned to the same site to moult the following year. One bird moulted at a nearby pan (5 km away), two moulted at estuaries less than 30 km from Strandfontein and one bird moulted at a farm dam 56 km away. Two birds satellite-tagged at  Strandfontein did not moult the following year and returned to moult at Strandfontein in the third year. The moult-site fidelity model suggested that a minimum of 16% of Barberspan birds and 51% of Strandfontein birds returned to the same wetland to moult the following year. The apparent low moult-site fidelity at Barberspan suggested by colour-ring resightings may reflect the small  number of birds colour-ringed at the site.Key words: waterfowl, Egyptian goose, southern Africa, telemetry, colour-ring