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Ticks and tick-borne pathogens can have considerable impacts on the health of livestock, wildlife... more Ticks and tick-borne pathogens can have considerable impacts on the health of livestock, wildlife and people. Knowledge of tick-host preferences is necessary for both tick and pathogen control. Ticks were historically considered as specialist parasites, but the range of sampled host species has been limited, infestation intensity has not been included in prior analyses, and phylogenetic distances between hosts have not been previously considered. We used a large dataset of 35 604 individual collections and two host-specificity indices to assess the specificity of 61 South African tick species, as well as distinctions between adult and juvenile ticks, for 95 mammalian hosts. When accounting for host phylogeny, most adult and juvenile ticks behaved as generalists, with juveniles being significantly more generalist than adults. When we included the intensity of tick infestation, ticks exhibited a wider diversity of specificity in all life stages. Our results show that ticks of mammals in South Africa tend to behave largely as generalists and that adult ticks are more host-specific. More generally, our analysis shows that the incorporation of life-stage differences, infestation intensity and phylogenetic distances between hosts, as well as the use of more than one specificity index, can all contribute to a deeper understanding of host-parasite interactions.
The timing and location of reproduction are fundamental elements of reproductive success for all ... more The timing and location of reproduction are fundamental elements of reproductive success for all organisms. Understanding why animals choose to reproduce at particular times and in particular places is also important for our understanding of other aspects of organismal ecology, such as their habitat requirements, movement strategies, and biogeography. Although breeding patterns in waterfowl are relatively well documented, most studies are from northern temperate regions and the influences of location and time of year on breeding in Afrotropical ducks (Anatidae) are poorly understood. We outline six alternative (but not mutually exclusive) hypotheses that might explain where and when Afrotropical ducks choose to breed. To explore these hypotheses, we assembled and analyzed a new database of c. 22,000 breeding records for 16 Afrotropical ducks and one introduced Palearctic species (the Mallard Anas platyrhynchos). The full database is available on line as an appendix to this article. We identified five distinct breeding strategies as well as two outliers. Peak breeding for 9 of 16 indigenous duck species occurs during the dry season. We found no evidence for spatial synchrony or spatial autocorrelation in breeding, suggesting a high level of flexibility in waterfowl responses to prevailing conditions in any given year. More intensive analyses of alternative hypotheses are needed, but our initial analysis suggests that the timing of breeding for the majority of Afrotropical ducks is driven by a combination of resource availability and predation risk.
Background/Question/Methods Functional responses in habitat selection can occur when animals must... more Background/Question/Methods Functional responses in habitat selection can occur when animals must choose between habitats that provide contrasting resources (e.g., quality forage vs. safety from predators), resulting in habitat use that is dependent on habitat availability. The majority of studies have examined these trade-offs in large mammals living at high latitudes in the northern hemisphere. Little research has been done on habitat choices faced by nomadic animals that occupy landscapes with unpredictable changes in resource distributions. To understand limiting factors at the home-range scale, we investigated the forage-predation risk trade-off of the semi-nomadic Egyptian Goose (Alopochen aegyptiaca) by analysing its habitat selection and functional responses. Using 12 months of fine-scale telemetry data for 10 Egyptian Geese tagged in two contrasting landscapes within South Africa, we examined: (1) how habitat selection for habitat types varied across seasons, sites, and lif...
... Ran Nathan Bruce D. Patterson Petr Pyek Marcel Rejmánek Anthony Ricciardi Mark Robertson Jon... more ... Ran Nathan Bruce D. Patterson Petr Pyek Marcel Rejmánek Anthony Ricciardi Mark Robertson Jon Paul Rodriguez Mathieu Rouget Nathan Sanders ... Negro, KA Hobson, GR Bortolotti and KL Bildstein: Can a 'wintering area effect' explain population status of Swainson's hawks ...
ABSTRACT Background/Question/Methods Biogeography has long acknowledged movement as an important ... more ABSTRACT Background/Question/Methods Biogeography has long acknowledged movement as an important influence on patterns of species occurrences. Incorporation of movement into biogeographic studies has often, however, been undertaken in a relatively simple way. We argue that unpacking the concept of dispersal into the fundamental elements of movement (internal drivers, external drivers, navigation capacity, and motion capacity) provides a better basis for contrasting competing hypotheses in biogeographic studies. We illustrate the value of taking a deeper perspective on movement with a case study that uses extensive satellite telemetry data from 26 Afrotropical ducks of two species, Red-billed Teal Anas erythrorhyncha and Egyptian Goose Alopochen aegyptiaca, at three different southern African study sites spread across a 17-degree latitudinal gradient. Movement paths from individual birds were analysed using Matlab to obtain estimates of a range of relevant parameters for each bird (e.g., mean and total distances moved, speed of movement, degree of resighting point aggregation, and turning angles). These data were then compared by species and site. Results/Conclusions Unexpectedly, Red-billed Teal, a ‘highly nomadic’ species, moved with a relatively high degree of consistency at each of our three different study latitudes, while Egyptian Geese, a ‘resident’ species, showed latitude-dependent variation in their movements. However, much of the latitude-related variation for Egyptian Geese was driven by their annual moult migrations, rather than directly by fluctuations in resource availability. Internal factors appear to dominate movements and probably determine the species ranges of both of our study species. Biogeographic patterns in this taxon may thus be best understood (and modelled) as a long-term response to environmental stochasticity, rather than as a deliberate selection of optimal habitat. More generally, our analysis suggests several ways in which movement ecology and biogeography could be more tightly linked, to the benefit of both areas of research.
Ticks and tick-borne pathogens can have considerable impacts on the health of livestock, wildlife... more Ticks and tick-borne pathogens can have considerable impacts on the health of livestock, wildlife and people. Knowledge of tick-host preferences is necessary for both tick and pathogen control. Ticks were historically considered as specialist parasites, but the range of sampled host species has been limited, infestation intensity has not been included in prior analyses, and phylogenetic distances between hosts have not been previously considered. We used a large dataset of 35 604 individual collections and two host-specificity indices to assess the specificity of 61 South African tick species, as well as distinctions between adult and juvenile ticks, for 95 mammalian hosts. When accounting for host phylogeny, most adult and juvenile ticks behaved as generalists, with juveniles being significantly more generalist than adults. When we included the intensity of tick infestation, ticks exhibited a wider diversity of specificity in all life stages. Our results show that ticks of mammals in South Africa tend to behave largely as generalists and that adult ticks are more host-specific. More generally, our analysis shows that the incorporation of life-stage differences, infestation intensity and phylogenetic distances between hosts, as well as the use of more than one specificity index, can all contribute to a deeper understanding of host-parasite interactions.
The timing and location of reproduction are fundamental elements of reproductive success for all ... more The timing and location of reproduction are fundamental elements of reproductive success for all organisms. Understanding why animals choose to reproduce at particular times and in particular places is also important for our understanding of other aspects of organismal ecology, such as their habitat requirements, movement strategies, and biogeography. Although breeding patterns in waterfowl are relatively well documented, most studies are from northern temperate regions and the influences of location and time of year on breeding in Afrotropical ducks (Anatidae) are poorly understood. We outline six alternative (but not mutually exclusive) hypotheses that might explain where and when Afrotropical ducks choose to breed. To explore these hypotheses, we assembled and analyzed a new database of c. 22,000 breeding records for 16 Afrotropical ducks and one introduced Palearctic species (the Mallard Anas platyrhynchos). The full database is available on line as an appendix to this article. We identified five distinct breeding strategies as well as two outliers. Peak breeding for 9 of 16 indigenous duck species occurs during the dry season. We found no evidence for spatial synchrony or spatial autocorrelation in breeding, suggesting a high level of flexibility in waterfowl responses to prevailing conditions in any given year. More intensive analyses of alternative hypotheses are needed, but our initial analysis suggests that the timing of breeding for the majority of Afrotropical ducks is driven by a combination of resource availability and predation risk.
Background/Question/Methods Functional responses in habitat selection can occur when animals must... more Background/Question/Methods Functional responses in habitat selection can occur when animals must choose between habitats that provide contrasting resources (e.g., quality forage vs. safety from predators), resulting in habitat use that is dependent on habitat availability. The majority of studies have examined these trade-offs in large mammals living at high latitudes in the northern hemisphere. Little research has been done on habitat choices faced by nomadic animals that occupy landscapes with unpredictable changes in resource distributions. To understand limiting factors at the home-range scale, we investigated the forage-predation risk trade-off of the semi-nomadic Egyptian Goose (Alopochen aegyptiaca) by analysing its habitat selection and functional responses. Using 12 months of fine-scale telemetry data for 10 Egyptian Geese tagged in two contrasting landscapes within South Africa, we examined: (1) how habitat selection for habitat types varied across seasons, sites, and lif...
... Ran Nathan Bruce D. Patterson Petr Pyek Marcel Rejmánek Anthony Ricciardi Mark Robertson Jon... more ... Ran Nathan Bruce D. Patterson Petr Pyek Marcel Rejmánek Anthony Ricciardi Mark Robertson Jon Paul Rodriguez Mathieu Rouget Nathan Sanders ... Negro, KA Hobson, GR Bortolotti and KL Bildstein: Can a 'wintering area effect' explain population status of Swainson's hawks ...
ABSTRACT Background/Question/Methods Biogeography has long acknowledged movement as an important ... more ABSTRACT Background/Question/Methods Biogeography has long acknowledged movement as an important influence on patterns of species occurrences. Incorporation of movement into biogeographic studies has often, however, been undertaken in a relatively simple way. We argue that unpacking the concept of dispersal into the fundamental elements of movement (internal drivers, external drivers, navigation capacity, and motion capacity) provides a better basis for contrasting competing hypotheses in biogeographic studies. We illustrate the value of taking a deeper perspective on movement with a case study that uses extensive satellite telemetry data from 26 Afrotropical ducks of two species, Red-billed Teal Anas erythrorhyncha and Egyptian Goose Alopochen aegyptiaca, at three different southern African study sites spread across a 17-degree latitudinal gradient. Movement paths from individual birds were analysed using Matlab to obtain estimates of a range of relevant parameters for each bird (e.g., mean and total distances moved, speed of movement, degree of resighting point aggregation, and turning angles). These data were then compared by species and site. Results/Conclusions Unexpectedly, Red-billed Teal, a ‘highly nomadic’ species, moved with a relatively high degree of consistency at each of our three different study latitudes, while Egyptian Geese, a ‘resident’ species, showed latitude-dependent variation in their movements. However, much of the latitude-related variation for Egyptian Geese was driven by their annual moult migrations, rather than directly by fluctuations in resource availability. Internal factors appear to dominate movements and probably determine the species ranges of both of our study species. Biogeographic patterns in this taxon may thus be best understood (and modelled) as a long-term response to environmental stochasticity, rather than as a deliberate selection of optimal habitat. More generally, our analysis suggests several ways in which movement ecology and biogeography could be more tightly linked, to the benefit of both areas of research.
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