How do invasive plants impact African wild mammals?

Background: Large areas of land in Kenya have been invaded by introduced plant species. These invasions often have negative impacts on peoples' livelihoods, by reducing the forage value of rangelands for pastoral livestock1. However, the impacts of these invasions on wild mammals are not fully understood, yet these might have important implications for human-wildlife conflicts. Invasions of rangelands may affect habitat quality for wildlife species, and thus their movement, distribution and habitat use within a landscape, and we need this information in order to fully understand the ecological and human impacts that plant invasions have, and whether plant invasions exacerbate human-wildlife conflicts. To achieve coexistence of humans and wildlife within landscape, we need to better understand how both interact with plant invasions, and what the effect of invader removal will be, so that invader impacts and human-wildlife conflicts can be mitigated effectively. This project will assess the distribution and habitat use of wild mammals in landscapes of Laikipia county (Kenya) in relation to invasions by prickly pear cacti (Opuntia), which are known to form monospecific stands that impede wild and livestock animal movements. Some of these invasions have been subjected to biological control, which offers an opportunity to understand how mammal distributions may change over time after invader removal.

Aims: In this project, the PhD candidate will address the following four questions:
1) How do invasions affect the distribution and movement of wild mammals in the landscape?
2) What is the distribution of human-wildlife conflicts within the landscape?
3) Do current invasions create a 'landscape of avoidance', that increases the likelihood of human-wildlife encounters and conflicts?
4) What are the impacts of biological control of plant invasions, on wild mammal movement and distribution?

Methods: Q1 will be addressed using camera-trapping and occupancy analysis methods2 to estimate and model the density and movement of wildlife in the landscape. These methods have been used to monitor the distribution of invasive mammals in landscapes, but have not yet been used to assess how invasive plants related to native mammal distributions. Q2 will be addressed with surveys of local households and cultural mapping techniques3 to map and categorise conflicts in the landscape. Habitat surveys, remote sensing and GIS will be used to capture information on landscape status (invaded, not invaded; used or not used by farmers), and other landscape features (catchments, settlements, elevation). These data will then be used to build landscape models, which will allow us to test, using data on animal densities and movements, whether plant invasions create a 'landscape of avoidance' leading to increased risk of human-wildlife conflicts (Q3).
Q4 will be addressed using camera-trapping and habitat selection models in a survey area that includes areas where Opuntia biological control has been undertaken, to assess, how wild mammal movement and distribution are impacted by Opuntia removal.

References: 1. Shackleton et al. (2017) African Journal of Range and Forage Science doi: 10.2989/10220119.2017.1301551; 2. Davis et al. (2018) Biological Invasions 20: 877-890; 3. Constant et al. (2015) Biodiversity and Conservation 24(12): 2967-2989.