Guy F. Midgley

Bio: Guy F. Midgley is an academic researcher from Stellenbosch University. The author has contributed to research in topics: Climate change & Biodiversity. The author has an hindex of 66, co-authored 217 publications receiving 30649 citations. Previous affiliations of Guy F. Midgley include University of Cape Town & International Union for Conservation of Nature and Natural Resources.

A fundamental, eco-hydrological basis for niche segregation in plant communities

Abstract: • Ecologists still puzzle over how plant species manage to coexist with one another while competing for the same essential resources. The classic answer for animal communities is that species occupy different niches, but how plants do this is more difficult to determine. We previously found niche segregation along fine-scale hydrological gradients in European wet meadows and proposed that the mechanism might be a general one, especially in communities that experience seasonal saturation. • We quantified the hydrological niches of 96 species from eight fynbos communities in the biodiversity hotspot of the Cape Floristic Region, South Africa and 99 species from 18 lowland wet meadow communities in the UK. Niche overlap was computed for all combinations of species. • Despite the extreme functional and phylogenetic differences between the fynbos and wet meadow communities, an identical trade-off (i.e. specialization of species towards tolerance of aeration and/or drying stress) was found to cause segregation along fine-scale hydrological gradients. • This study not only confirms the predicted generality of hydrological niche segregation, but also emphasizes its importance for structuring plant communities. Eco-hydrological niche segregation will have implications for conservation in habitats that face changing hydrology caused by water abstraction and climate change.

Migration rate limitations on climate change-induced range shifts in Cape Proteaceae

Abstract: Modelling of climate change-induced species range shifts has generally addressed migration limitations inadequately, often assuming ‘null’ migration or instantaneous ‘full’ migration extremes. We describe methods for incorporating simple migration rate assumptions into multispecies modelling, using the Proteaceae of the Cape Floristic Region. Even with optimistic migration assumptions, range loss projections more closely approximate null migration than full migration assumptions. Full migration results were positively skewed by few species with large range increases, an overestimate eliminated by dispersal-limited migration rate assumptions. Wind- and ant/rodent-dispersed species responded differently to climate change. Initially larger ranges of wind-dispersed species were more strongly reduced by climate change, despite far greater assumed dispersal distances — we suggest that these well-dispersed species populate more marginal areas of potential range, causing lower resilience to climatic changes at range margins. Overall, range loss rate slowed with advancing climate change, possibly because species ranges contracted into core areas most resilient to climate change. Thus, a consideration of simple dynamics of range change (rather than single step, present–future comparisons of range) provide new insights relevant for conservation strategies, in particular, and for guiding monitoring efforts to detect and gauge the impacts of climate change on natural populations.

Will Climate Change Promote Alien Plant Invasions

Abstract: Invasive alien plant species pose significant challenges to managing and maintaining indigenous biodiversity in natural ecosystems. Invasive plants can transform ecosystems by establishing viable populations with growth rates high enough to displace elements of the native biota (Rejmánek 1999) or to modify disturbance regimes (Brooks et al. 2004), thereby potentially transforming ecosystem structure and functioning (Dukes and Mooney 2004). Because the numbers of invasive plant species and the extent of invasions are increasing rapidly in many regions, concern has grown about the stability of these novel, emerging ecosystems (Hobbs et al. 2006). The question of how climate change will interact in this global process of ecosystem modification is becoming highly relevant for natural resource management. Although many studies have addressed the potential threats to ecosystems from invasive alien plants and climate change separately, few studies have considered the interactive and potentially synergistic impacts of these two factors on ecosystems (but see Ziska 2003). Climatic and landscape features set the ultimate limits to the geographic distribution of species and determine the seasonal conditions for establishment, recruitment, growth and survival (Rejmánek and Richardson 1996; Thuiller et al. 2006b). Human-induced climate change is therefore a pervasive element of the multiple forcing functions which maintain, generate and threaten natural biodiversity. A widely stated view is that climate change is likely to enhance the capacity of alien species to invade new areas, while simultaneously decreasing the resistance to invasion of natural communities by disturbing the dynamic equilibrium maintaining them. Links between invasion dynamics and climate change are, nevertheless, particularly difficult to conceptualize (Fig. 12.1). The determinants of plant invasiveness per se are extremely complex (Rejmánek et al. 2005). Consequently, efforts to combat plant invasions

A changing climate is eroding the geographical range of the Namib Desert tree Aloe through population declines and dispersal lags

Abstract: While poleward species migration in response to recent climatic warming is widely documented, few studies have examined entire range responses of broadly distributed sessile organisms, including changes on both the trailing (equatorward) and the leading (poleward) range edges. From a detailed population census throughout the entire geographical range of Aloe dichotoma Masson, a long-lived Namib Desert tree, together with data from repeat photographs, we present strong evidence that a developing range shift in this species is a ‘fingerprint’ of anthropogenic climate change. This is explained at a high level of statistical significance by population level impacts of observed regional warming and resulting water balance constraints. Generalized linear models suggest that greater mortalities and population declines in equatorward populations are virtually certainly the result, due to anthropogenic climate change, of the progressive exceedance of critical climate thresholds that are relatively closer to the species’ tolerance limits in equatorward sites. Equatorward population declines are also broadly consistent with bioclimatically modelled projections under anticipated anthropogenic climate change but, as yet, there is no evidence of poleward range expansion into the area predicted to become suitable in future, despite good evidence for positive population growth trends in poleward populations. This study is among the first to show a marked lag between trailing edge population extinction and leading edge range expansion in a species experiencing anthropogenic climate change impacts, a pattern likely to apply to most sessile and poorly dispersed organisms. This provides support for conservative assumptions of species’ migration rates when modelling climate change impacts for such species. Aloe dichotoma ’s response to climate change suggests that desert ecosystems may be more sensitive to climate change than previously suspected.

Biodiversity and Ecosystem Function

Abstract: How is the biodiversity within an ecosystem related to the ecosystem's function? Quantifying and understanding this relationship—the biodiversity-ecosystem function (BEF) ( 1 )—is important because socio-economic development is almost always accompanied by the loss of natural habitat and species ( 2 ). Short-term economic gains may thus trump longer-term benefits for human society, creating vulnerabilities that could be avoided or corrected with enough knowledge about the role of biodiversity. Erosion of biodiversity at local and regional scales may also reduce resilience at larger spatial scales as a result of degradation of ecosystem function ( 3 ). On page 214 of this issue, Maestre et al. ( 4 ) report an important step toward extending our understanding of BEF to globally important ecosystems.

Food Security: The Challenge of Feeding 9 Billion People

Abstract: Continuing population and consumption growth will mean that the global demand for food will increase for at least another 40 years. Growing competition for land, water, and energy, in addition to the overexploitation of fisheries, will affect our ability to produce food, as will the urgent requirement to reduce the impact of the food system on the environment. The effects of climate change are a further threat. But the world can produce more food and can ensure that it is used more efficiently and equitably. A multifaceted and linked global strategy is needed to ensure sustainable and equitable food security, different components of which are explored here.

Novel methods improve prediction of species' distributions from occurrence data

Abstract: Prediction of species' distributions is central to diverse applications in ecology, evolution and conservation science. There is increasing electronic access to vast sets of occurrence records in museums and herbaria, yet little effective guidance on how best to use this information in the context of numerous approaches for modelling distributions. To meet this need, we compared 16 modelling methods over 226 species from 6 regions of the world, creating the most comprehensive set of model comparisons to date. We used presence-only data to fit models, and independent presence-absence data to evaluate the predictions. Along with well-established modelling methods such as generalised additive models and GARP and BIOCLIM, we explored methods that either have been developed recently or have rarely been applied to modelling species' distributions. These include machine-learning methods and community models, both of which have features that may make them particularly well suited to noisy or sparse information, as is typical of species' occurrence data. Presence-only data were effective for modelling species' distributions for many species and regions. The novel methods consistently outperformed more established methods. The results of our analysis are promising for the use of data from museums and herbaria, especially as methods suited to the noise inherent in such data improve.

Extinction risk from climate change

Abstract: Climate change over the past approximately 30 years has produced numerous shifts in the distributions and abundances of species and has been implicated in one species-level extinction. Using projections of species' distributions for future climate scenarios, we assess extinction risks for sample regions that cover some 20% of the Earth's terrestrial surface. Exploring three approaches in which the estimated probability of extinction shows a power-law relationship with geographical range size, we predict, on the basis of mid-range climate-warming scenarios for 2050, that 15-37% of species in our sample of regions and taxa will be 'committed to extinction'. When the average of the three methods and two dispersal scenarios is taken, minimal climate-warming scenarios produce lower projections of species committed to extinction ( approximately 18%) than mid-range ( approximately 24%) and maximum-change ( approximately 35%) scenarios. These estimates show the importance of rapid implementation of technologies to decrease greenhouse gas emissions and strategies for carbon sequestration.