Guy F. Midgley

Predicting extinction risks under climate change: coupling stochastic population models with dynamic bioclimatic habitat models

Species responses to climate change may be influenced by changes in available habitat, as well as population processes, species interactions and interactions between demographic and landscape dynamics. Current methods for assessing these responses fail to provide an integrated view of these influences because they deal with habitat change or population dynamics, but rarely both. In this study, we linked a time series of habitat suitability models with spatially explicit stochastic population models to explore factors that influence the viability of plant species populations under stable and changing climate scenarios in South African fynbos, a global biodiversity hot spot. Results indicate that complex interactions between life history, disturbance regime and distribution pattern mediate species extinction risks under climate change. Our novel mechanistic approach allows more complete and direct appraisal of future biotic responses than do static bioclimatic habitat modelling approaches, and will ultimately support development of more effective conservation strategies to mitigate biodiversity losses due to climate change.

Protected area needs in a changing climate

Range shifts due to climate change may cause species to move out of protected areas. Climate change could therefore result in species range dynamics that reduce the relevance of current fixed protected areas in future conservation strategies. Here, we apply species distribution modeling and conservation planning tools in three regions (Mexico, the Cape Floristic Region of South Africa, and Western Europe) to examine the need for additional protected areas in light of anticipated species range shifts caused by climate change. We set species representation targets and assessed the area required to meet those targets in the present and in the future, under a moderate climate change scenario. Our findings indicate that protected areas can be an important conservation strategy in such a scenario, and that early action may be both more effective and less costly than inaction or delayed action. According to our projections, costs may vary among regions and none of the three areas studied will fully meet all conservation targets, even under a moderate climate change scenario. This suggests that limiting climate change is an essential complement to adding protected areas for conservation of biodiversity.

Forecasting Regional to Global Plant Migration in Response to Climate Change

Abstract The rate of future climate change is likely to exceed the migration rates of most plant species. The replacement of dominant species by locally rare species may require decades, and extinctions may occur when plant species cannot migrate fast enough to escape the consequences of climate change. Such lags may impair ecosystem services, such as carbon sequestration and clean water production. Thus, to assess global change, simulation of plant migration and local vegetation change by dynamic global vegetation models (DGVMs) is critical, yet fraught with challenges. Global vegetation models cannot simulate all species, necessitating their aggregation into plant functional types (PFTs). Yet most PFTs encompass the full spectrum of migration rates. Migration processes span scales of time and space far beyond what can be confidently simulated in DGVMs. Theories about climate change and migration are limited by inadequate data for key processes at short and long time scales and at small and large spatial scales. These theories must be enhanced to incorporate species-level migration and succession processes into a more comprehensive definition of PFTs.

Developing regional and species-level assessments of climate change impacts on biodiversity in the Cape Floristic Region

We assess the potential impact of climate change on plant diversity in the Cape Floristic Region (CFR) and its interaction with land transformation that has already occurred in the region. Predictions were made both at the scale of the Fynbos Biome (the dominant vegetation assemblage in the CFR) and for selected Proteaceae species. Bioclimatic modelling identified parts of the biome at particular risk from climate change. Species-level modelling (Generalised Additive Modelling) was done for 28 Proteaceae species selected from areas at high risk of biome loss, revealing individualistic range changes in a pattern broadly consistent with biome modelling results. Most species experienced potential range contractions (17 of 28), of which five showed range elimination. Several species (11 of 28) showed potential range expansions. For species showing range contractions, current land transformation had less impact on future potential ranges than did climate change, because many species ranges shifted to higher altitudes where land transformation is currently less prevalent. Fewer than half of the high-risk species showed overlap between current and future potential range, showing that propagule transport, establishment of species in novel ranges and conservation of landscape linkages will be critical for maintenance of biodiversity. Methods described here provide useful forecasts of potential climate change impacts that could guide conservation responses, but results need cautious interpretation in the light of the many assumptions underlying the techniques used.

Carbon dioxide and the uneasy interactions of trees and savannah grasses.

Savannahs are a mixture of trees and grasses often occurring as alternate states to closed forests. Savannah fires are frequent where grass productivity is high in the wet season. Fires help maintain grassy vegetation where the climate is suitable for woodlands or forests. Saplings in savannahs are particularly vulnerable to topkill of above-ground biomass. Larger trees are more fire-resistant and suffer little damage when burnt. Recruitment to large mature tree size classes depends on sapling growth rates to fire-resistant sizes and the time between fires. Carbon dioxide (CO2) can influence the growth rate of juvenile plants, thereby affecting tree recruitment and the conversion of open savannahs to woodlands. Trees have increased in many savannahs throughout the world, whereas some humid savannahs are being invaded by forests. CO2 has been implicated in this woody increase but attribution to global drivers has been controversial where changes in grazing and fire have also occurred. We report on diverse tests of the magnitude of CO2 effects on both ancient and modern ecosystems with a particular focus on African savannahs. Large increases in trees of mesic savannahs in the region cannot easily be explained by land use change but are consistent with experimental and simulation studies of CO2 effects. Changes in arid savannahs seem less obviously linked to CO2 effects and may be driven more by overgrazing. Large-scale shifts in the tree–grass balance in the past and the future need to be better understood. They not only have major impacts on the ecology of grassy ecosystems but also on Earth–atmosphere linkages and the global carbon cycle in ways that are still being discovered.

The View from the Cape: Extinction Risk, Protected Areas, and Climate Change

Abstract In the past decade, a growing number of studies have modeled the effects of climate change on large numbers of species across diverse focal regions. Many common points emerge from these studies, but it can be difficult to understand the consequences for conservation when data for large numbers of species are summarized. Here we use an in-depth example, the multispecies modeling effort that has been conducted for the proteas of the Cape Floristic Region of South Africa, to illustrate lessons learned in this and other multispecies modeling efforts. Modeling shows that a substantial number of species may lose all suitable range and many may lose all representation in protected areas as a result of climate change, while a much larger number may experience major loss in the amount of their range that is protected. The spatial distribution of protected areas, particularly between lowlands and uplands, is an important determinant of the likely conservation consequences of climate change.

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

• 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.

Diverse functional responses to drought in a Mediterranean-type shrubland in South Africa

• Mediterranean-type ecosystems contain 20% of all vascular plant diversity on Earth and have been identified as being particularly threatened by future increases in drought. Of particular concern is the Cape Floral Region of South Africa, a global biodiversity hotspot, yet there are limited experimental data to validate predicted impacts on the flora. In a field rainout experiment, we tested whether rooting depth and degree of isohydry or anisohydry could aid in the functional classification of drought responses across diverse growth forms. • We imposed a 6-month summer drought, for 2 yr, in a mountain fynbos shrubland. We monitored a suite of parameters, from physiological traits to morphological outcomes, in seven species comprising the three dominant growth forms (deep-rooted proteoid shrubs, shallow-rooted ericoid shrubs and graminoid restioids). • There was considerable variation in drought response both between and within the growth forms. The shallow-rooted, anisohydric ericoid shrubs all suffered considerable reductions in growth and flowering and increased mortality. By contrast, the shallow-rooted, isohydric restioids and deep-rooted, isohydric proteoid shrubs were largely unaffected by the drought. • Rooting depth and degree of iso/anisohydry allow a first-order functional classification of drought response pathways in this flora. Consideration of additional traits would further refine this approach.

An ecological economic simulation model of mountain fynbos ecosystems: Dynamics, valuation and management

Abstract Mountain fynbos ecosystems in South Africa are threatened by alien plant invasions and by a lack of funding for effective management of these invasions. This paper develops an ecological-economic argument for the effective management of plant invasions in mountain fynbos ecosystems. We do this by building a dynamic ecological economic model which values the ecosystem services that fynbos ecosystems provide under different management regimes. We propose that the services that mountain fynbos ecosystems provide fall into six components: water production, wildflower harvest, hiker visitation, ecotourist visitation, endemic species and genetic storage. A scenario analysis based on a hypothetical 4 km2 mountain fynbos ecosystem in the western part of the fynbos biome estimated that the ecosystems value varies from R19 million (under low valuation and poor management scenario) to R300 million (under high valuation and good management scenario) [R4.50=US

Climate change and birds: perspectives and prospects from southern Africa

1]. Water production and genetic storage were the most valuable ecosystem services. The model showed that the cost of clearing alien plants (under the proactive management scenario) was a tiny (0.6–5%) proportion of the value of mountain fynbos ecosystems. This result motivates an injection of funds for clearing alien plants from mountain fynbos ecosystems.