Browsing by Author "Le Roux, Peter C."

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Exploring South Africa’s southern frontier : a 20-year vision for polar research through the South African National Antarctic Programme
    (Academy of Science of South Africa, 2017) Ansorge, Isabelle J.; Skelton, Paul; Bekker, Annie; de Bruyn, P.J. Nico; Butterworth, Doug; Cilliers, Pierre; Cooper, John; Cowan, Don A.; Dorrington, Rosemary; Fawcett, Sarah; Fietz, Susanne; Findlay, Ken P.; Froneman, William P.; Grantham, Geoff H.; Greve, Michelle; Hedding, David; Hofmeyr, Greg G. J.; Kosch, Michael; Le Roux, Peter C.; Lucas, Mike; MacHutchon, Keith; Meiklejohn, Ian; Nel, Werner; Pistorius, Pierre; Ryan, Peter G.; Stander, Johan; Swart, Sebastiaan; Treasure, Anne; Vichi, Marcello; Van Vuuren, Bettine J.
    No abstract available
  • Thumbnail Image
    Item
    The influence of life history characteristics on flea (Siphonaptera) species distribution models
    (BioMed Central, 2016) Van der Mescht, Luther; Le Roux, Peter C.; Matthee, Conrad A.; Raath, Morgan J.; Matthee, Sonja
    Background: Ectoparasites exhibit pronounced variation in life history characteristics such as time spent on the host and host range. Since contemporary species distribution (SD) modelling does not account for differences in life history, the accuracy of predictions of current and future species’ ranges could differ significantly between life history groups. Results SD model performance was compared between 21 flea species that differ in microhabitat preferences and level of host specificity. Distribution models generally performed well, with no significant differences in model performance based on either microhabitat preferences or host specificity. However, the relative importance of predictor variables was significantly related to host specificity, with the distribution of host-opportunistic fleas strongly limited by thermal conditions and host-specific fleas more associated with conditions that restrict their hosts’ distribution. The importance of temperature was even more pronounced when considering microhabitat preference, with the distribution of fur fleas being strongly limited by thermal conditions and nest fleas more associated with variables that affect microclimatic conditions in the host nest. Conclusions Contemporary SD modelling, that includes climate and landscape variables, is a valuable tool to study the biogeography and future distributions of fleas and other parasites taxa. However, consideration of life history characteristics is cautioned as species may be differentially sensitive to environmental conditions.
  • Thumbnail Image
    Item
    Ontogenetic shifts in plant interactions vary with environmental severity and affect population structure
    (Wiley Online Library, 2013) Le Roux, Peter C.; Shaw, Justine D.; Chown, Steven L.
    Environmental conditions and plant size may both alter the outcome of inter‐specific plant–plant interactions, with seedlings generally facilitated more strongly than larger individuals in stressful habitats. However, the combined impact of plant size and environmental severity on interactions is poorly understood. Here, we tested explicitly for the first time the hypothesis that ontogenetic shifts in interactions are delayed under increasingly severe conditions by examining the interaction between a grass, Agrostis magellanica, and a cushion plant, Azorella selago, along two severity gradients. The impact of A. selago on A. magellanica abundance, but not reproductive effort, was related to A. magellanica size, with a trend for delayed shifts towards more negative interactions under greater environmental severity. Intermediate‐sized individuals were most strongly facilitated, leading to differences in the size‐class distribution of A. magellanica on the soil and on A. selago. The A. magellanica size‐class distribution was more strongly affected by A. selago than by environmental severity, demonstrating that the plant–plant interaction impacts A. magellanica population structure more strongly than habitat conditions. As ontogenetic shifts in plant–plant interactions cannot be assumed to be constant across severity gradients and may impact species population structure, studies examining the outcome of interactions need to consider the potential for size‐ or age‐related variation in competition and facilitation.
  • Thumbnail Image
    Item
    Species-energy relationships of indigenous and invasive species may arise in different ways – a demonstration using springtails
    (Nature Publishing Group, 2019-09-24) Treasure, Anne M.; Le Roux, Peter C.; Mashau, Mashudu H.; Chown, Steven L.
    ENGLISH ABSTRACT: Although the relationship between species richness and available energy is well established for a range of spatial scales, exploration of the plausible underlying explanations for this relationship is less common. Speciation, extinction, dispersal and environmental filters all play a role. Here we make use of replicated elevational transects and the insights offered by comparing indigenous and invasive species to test four proximal mechanisms that have been offered to explain relationships between energy availability, abundance and species richness: the sampling mechanism (a null expectation), and the more individuals, dynamic equilibrium and range limitation mechanisms. We also briefly consider the time for speciation mechanism. We do so for springtails on sub-Antarctic Marion Island. Relationships between energy availability and species richness are stronger for invasive than indigenous species, with geometric constraints and area variation playing minor roles. We reject the sampling and more individuals mechanisms, but show that dynamic equilibrium and range limitation are plausible mechanisms underlying these gradients, especially for invasive species. Time for speciation cannot be ruled out as contributing to richness variation in the indigenous species. Differences between the indigenous and invasive species highlight the ways in which deconstruction of richness gradients may usefully inform investigations of the mechanisms underlying them. They also point to the importance of population size-related mechanisms in accounting for such variation. In the context of the sub-Antarctic our findings suggest that warming climates may favour invasive over indigenous species in the context of changes to elevational distributions, a situation found for vascular plants, and predicted for springtails on the basis of smaller-scale manipulative field experiments.