Browsing by Author "Vanmali, Namita Madhu"

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    Assessing the feasibility of assisted colonisation to reduce climate change extinction risk for Western Cape proteaceae
    (Stellenbosch : Stellenbosch University, 2021-12) Vanmali, Namita Madhu; Midgley, Guy F.; Foden, Wendy
    ENGLISH ABSTRACT: Anthropogenic climate change may be testing certain species’ abilities to adapt via range migration, or natural selection in situ. Particularly vulnerable species have restricted ranges and limited dispersal capabilities – characteristics of many endemic species found in the Cape Floristic Region (CFR). Many have evolved anti-telechory, including several Proteaceae species, and may thus require active conservation interventions to ensure their future persistence in the wild. Assisted Colonisation (AC) is a conservation strategy aimed at reducing species’ climate change-induced extinction risk, but no detailed assessments exist of the feasibility of assisted colonisation in the CFR context. By combining Species Distribution Modelling (SDM) outputs for 191 Proteaceae species under future climate scenarios, with selected species traits and land-use maps, this study developed a hierarchical screening approach to identify potential assisted colonisation candidates in the CFR. Using projections over shorter time periods allowed for more potential assisted colonisation candidates to be identified and using life-history traits in conjunction with spatial projections shifted the prioritisation of some assisted colonisation candidates. Thirty-one potential assisted colonisation candidates were identified and subset into three types: Sustained intervention, Short-term intervention, and Mitigation dependent candidates, indicating different degrees of active intervention. The Mitigation dependent candidate group highlighted the potential for future global emissions reductions to reduce extinction risk for several assisted colonisation candidate species projected to become highly vulnerable after 2040. Vulnerable species not suitable for assisted colonisation were also identified. Some implicit assumptions behind assisted colonisation implementation were explored using field measurements on selected populations of Protea compacta, a species historically planted and harvested for the cut flower industry. P. compacta allowed exploration of ecological performance differences across a range of environmental suitability levels. P. compacta populations were targeted in sites defined by species distribution models (SDMs) as having high bioclimatic suitability in ‘core’ range sites, supporting naturally established populations, and sites of ‘marginal’ bioclimatic suitability, occupied by artificially introduced populations. The latter represents a pragmatic assisted colonisation approach – establishing populations in marginal sites that are projected to become more suitable with progressive climate change. Microhabitat buffering against low suitability in a marginal site was also explored. Measurements unexpectedly showed individuals in marginal sites had higher growth and flowering rates, but higher disease susceptibility. Additionally, the densely populated core sites showed significantly more monopodial branching, and sympodial branching in marginal sites, suggesting that the relaxation of strong intraspecific competition in marginal sites may compensate for lower population densities, supporting population establishment, and thus favouring the practical implementation of assisted colonisation. This pattern was confirmed by a finer-scale study at a marginal site, where high population densities found in wetter microhabitats showed growth and flowering responses similar to those in core populations. This supports the idea that purposeful microhabitat choices may buffer marginal unsuitability and increase likelihood of successful assisted colonisation implementation. This work has allowed for a novel assessment of the feasibility of assisted colonisation in the CFR, but assessment of unintended consequences and generalising to more species and systems is necessary to further establish a basis for considering assisted colonisation implementation.