Browsing by Author "Maciejewski, Kristine"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Challenges and opportunities for monitoring wild Nile crocodiles with scute mark-recapture photography
    (AOSIS, 2018-07-19) Coetzee, Bernard W. T.; Ferreira, Sam M.; Maciejewski, Kristine
    ENGLISH ABSTRACT: The global conservation status of Nile crocodiles (Crocodylus niloticus) was last assessed in 1996. The species presents particular difficulty in monitoring because it can be cryptic, require expertise to handle, and caudal tail tags and transmitters are often lost. Some studies advocate mark-recapture techniques based on photograph identification of the unique scute markings of crocodile tails as a non-invasive means of monitoring their populations. Researchers developed this method with crocodiles in captivity. In this study, we test the technique under field conditions by monitoring crocodiles from 2015 to 2017 in the Sunset Dam in the Kruger National Park. Using a Cormack-Jolly-Seber open population model, we found that the dam may host 15–30 individuals, but that there is a high turnover of individuals and much uncertainty in model outputs. The dam’s population thus has high rates of immigration and emigration. The method proved challenging under field conditions, as there was bias in identifying scute markings consistently. The efficient use of the method requires an exceptional quality of photographic equipment. Animal crypsis, however, remains an issue. In this study, we discuss how to improve the mark-recapture photography methodology, especially to adapt the technique for citizen science initiatives. Conservation implications: Using scute mark-recapture photography presents challenges under field conditions. These challenges require innovative, practical and analytical solutions to successfully use the technique before monitoring programmes, aimed at ensuring the persistence of crocodiles in the wild, can be implemented.
  • Thumbnail Image
    Item
    Food system transformation : integrating a political–economy and social–ecological approach to regime shifts
    (2020-02) Pereira, Laura M.; Drimie, Scott; Maciejewski, Kristine; Tonissen, Patrick Bon; Biggs, Reinette, 1979-
    Sustainably achieving the goal of global food security is one of the greatest challenges of the 21st century. The current food system is failing to meet the needs of people, and at the same time, is having far-reaching impacts on the environment and undermining human well-being in other important ways. It is increasingly apparent that a deep transformation in the way we produce and consume food is needed in order to ensure a more just and sustainable future. This paper uses the concept of regime shifts to understand key drivers and innovations underlying past disruptions in the food system and to explore how they may help us think about desirable future changes and how we might leverage them. We combine two perspectives on regime shifts—one derived from natural sciences and the other from social sciences—to propose an interpretation of food regimes that draws on innovation theory. We use this conceptualization to discuss three examples of innovations that we argue helped enable critical regime shifts in the global food system in the past: the Haber-Bosch process of nitrogen fixation, the rise of the supermarket, and the call for more transparency in the food system to reconnect consumers with their food. This paper concludes with an exploration of why this combination of conceptual understandings is important across the Global North/ Global South divide, and proposes a new sustainability regime where transformative change is spearheaded by a variety of social–ecological innovations.
  • Thumbnail Image
    Item
    Temperature-dependent sex determination in the Nile crocodile, Crocodylus niloticus, in the Okavango River, Botswana, and the effect of global climate change
    (Stellenbosch : Stellenbosch University, 2006-12) Maciejewski, Kristine; Leslie, Alison J.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation of Ecology and Entomology.
    ENGLISH ABSTRACT: The Nile crocodile, Crocodylus niloticus exhibits temperature-dependent sex determination, where sex is determined by the incubation temperature of the egg prior to hatching. Laboratory incubation of the eggs indicated that the lower and upper pivotal temperature for the Nile crocodile in the Okavango River, Botswana was 31.4°C and 33.4°C respectively. Exclusively females were produced at a constant temperature of 30.0°C, 30.5°C and 34.0°C, 71% females were produced at 31.0°C and the majority males were produced at 31.5; 32.0; 32.5 and 33.0°C. Crocodylus niloticus in the Okavango Region therefore has a female-male-female pattern of temperaturedependent sex determination where females are produced at lower and higher incubation temperatures. Embryonic development, incubation period, hatching success and development rates were strongly temperature dependent. The location of nests plays an important role in determination of incubation temperature. At a distance of 6m from the river, soil temperature was at a maximum at a depth of 25cm. Breeding females choose nesting sites based on optimal soil temperatures. Along the Okavango River the average nest sites were 5.6m from the river, and the eggs were at an average depth of 24.5cm. Calculation of mean nest temperature during the thermosensitive period (sex determining period) of incubation for ten wild Nile crocodile nests indicated that the nests along the Okavango River are primarily female-biased. An increase in average air temperature due to Global Climate Change could possibly shift the population to a malebiased sex ratio, leading to eventual extinction of the Nile crocodile in the Okavango River. Stellenbosch University https://scholar.sun.ac.za