Peter le Roux

Peter le Roux
University of Pretoria | UP · Department of Plant and Soil Sciences

About

92
Publications
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Publications

Publications (92)
Article
Geomorphological processes profoundly affect plant establishment and distributions, but their influence on functional traits is insufficiently understood. Here, we unveil trait–geomorphology relationships in Arctic plant communities. High‐Arctic Svalbard, low‐Arctic Greenland and sub‐Arctic Fennoscandia. 2011–2018. Vascular plants. We collected fie...
Article
Questions Species distribution models have traditionally relied heavily on temperature and precipitation, often ignoring other potentially important variables. However, recent advances have shown other climatic variables, including snow cover and solar radiation, may strongly improve predictions of species occurrence. Wind has long been known to ha...
Article
Full-text available
Plant co-occurrence patterns can be driven by both abiotic and biotic conditions. Biotic interactions can affect the co-occurrence of seedlings and adult plants through the nurse effect, a form of facilitation where adult plants create favourable conditions for seedlings. However, other mechanisms, including seed trapping, can also cause the aggreg...
Article
Biotic modifiers are species that strongly alter environmental conditions, and that often shape local communities. When more than one biotic modifier co-occurs, the potential for interactive effects exists, where the effects of one species may negate or enhance the impacts of a second biotic modifier. Here we test for an interactive effect of aardv...
Article
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A fundamental assumption in trait-based ecology is that relationships between traits and environmental conditions are globally consistent. We use field-quantified microclimate and soil data to explore if trait–environment relationships are generalizable across plant communities and spatial scales. We collected data from 6,720 plots and 217 species...
Article
1. The effects of temperature and precipitation, and the impacts of changes in these climatic conditions, on plant communities have been investigated extensively. The roles of other climatic factors are, however, comparatively poorly understood, despite potentially also strongly structuring community patterns. Wind, for example, is seldom considere...
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The flora of sub-Antarctic Marion Island forms part of the unique South Indian Ocean Biogeographic Province, and is under threat from climate change and invasive species. Current information on the flora is necessary to rapidly identify and manage future changes. We conducted a literature search on the taxonomy of indigenous vascular plant species...
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AimsThe sub-Antarctic cushion plant, Azorella selago, is usually hemispherical when small but frequently crescent-shaped when larger. Spatial variation in wind speed and in air-borne seed and sediment deposition is examined to determine if wind scouring and deposition patterns could contribute to the development of non-hemispherical shapes in cushi...
Article
Positive biotic interactions between plant species may strongly affect species and community‐level patterns, but the processes through which benefactor species alter the performance of interacting species (via, e.g. beneficial mechanisms like resource provisioning) are still inadequately understood. One poorly explored potential explanation is that...
Article
Where inter-specific facilitation favors the establishment of high densities of a beneficiary species, strong intra-specific competition may subsequently impede beneficiary performance. Consequently, the negative influence of intra-specific competition between beneficiary individuals could potentially outweigh the positive influence of inter-specif...
Article
Ecosystem engineers influence community structure and functioning by altering habitat and resource availability. However, few studies have assessed how consistent ecosystem engineers' impacts are on abiotic habitat conditions and/or community characteristics, either across species or between habitats. Here we test for the consistency of ecosystem e...
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Plant traits—the morphological, anatomical, physiological, biochemical and phenological characteristics of plants—determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research sp...
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The impacts of ecosystem engineers may be expected to vary along environmental gradients. Due to some resources being more limited in arid than in mesic environments, disturbances created by burrowing mammals are expected to have a greater ameliorating effect in arid environments, with larger differences in microhabitat conditions expected between...
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Although the relationship between species richness and available energy is well established for a range of spatial scales, exploration of the plausible underlying explanations for this relationship is less common. Speciation, extinction, dispersal and environmental filters all play a role. Here we make use of replicated elevational transects and th...
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Biotic interactions can shape species’ distributions through their impact on species’ realized niches, potentially constraining or expanding the range of conditions under which species occur. We examine whether fine‐scale plant–plant interactions scale up to shape broad‐scale species’ distributions, using Azorella selago, a widespread cushion plant...
Article
Questions Invasive species establish either by possessing traits, or trait trade‐offs similar to native species, suggesting pre‐adaptation to local conditions; or by having a different suite of traits and trait trade‐offs, which allow them to occupy unfilled niches. The trait differences between invasives and non‐invasives can inform on which trait...
Article
Aim A common approach for prioritizing conservation is to identify concentrations (hotspots) of biodiversity. Such hotspots have traditionally been designated on the basis of species‐level metrics (e.g., species richness, endemism and extinction vulnerability). These approaches do not consider phylogenetics explicitly, although phylogenetic relatio...
Article
Water is crucial for plant productivity and survival as a fundamental resource, but water conditions can also cause physiological stress and mechanical disturbance to vegetation. However, these different influences of water on vegetation patterns have not been evaluated simultaneously. Here, we demonstrate the importance of three water aspects (spa...
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Current climate change is altering the distribution of species across both broad and fine scales. Examining contemporary species distributions along altitudinal gradients is one approach to predicting species future distributions, as species occurrence patterns at cold, high altitudes are expected to resemble the species distribution patterns curre...
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Cushion plants are a key Arctic, Antarctic, and alpine growth form, with many cushion-forming species strongly affecting community structure in abiotically stressful environments. Despite their ecological importance, there is little information about what drives the distribution of species exhibiting this growth form. This study investigates the de...
Article
Burrowing mammals are often considered to be ecosystem engineers as burrowing disturbs the soil, thereby potentially changing resource availability and affecting habitat conditions for other species. After their excavation, burrows may strongly impact local plant communities through several mechanisms, including resource trapping, altered chemical...
Conference Paper
The hydrological cycle of tundra has intensified due to accelerated environmental changes. Climatic changesaffect tundra vegetation by altering water conditions (1). Plant-available water mediates climate change impacts,namely against rising temperatures and changing snow dynamics (2). Vegetation is limited by water resources,but water forms also m...
Conference Paper
Global environmental change is altering water conditions in tundra. However, as the vegetation of these cold regions is considered to be energy-limited, the influence of water is often inadequately considered in studies of climate change impacts. Here, we shed light on the importance of water-related factors in shaping vegetation patterns in Europe...
Poster
Global environmental change is altering water conditions in tundra. However, as the vegetation of these cold regions is considered to be energy-limited, the influence of water is often inadequately considered in studies of climate change impacts. Here, we shed light on the importance of water-related factors in shaping vegetation patterns in Europe...
Article
Biotic interactions influence species niches and may thus shape distributions. Nevertheless, species distribution modelling has traditionally relied exclusively on environmental factors to predict species distributions, while biotic interactions have only seldom been incorporated into models. This study tested the ability of incorporating biotic in...
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Antarctica and the Southern Ocean form a critical natural laboratory where international scientific investigation can infer the fundamental drivers of the entire earth system and of the near-earth space environment. Advancing our understanding is critical to better comprehend the region’s role in global ocean-atmospheric circulation, ecosystem adap...
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Studies of community assembly focus on finding rules that predict which species can become member of a plant community. Within a community, species can be categorized in two ways: functional groups classify species according to their functional traits, whereas generalized guilds group species based on their (co-)occurrence, spatial distribution and...
Article
Arboreal ants use a variety of plant structures as nesting sites, but may also nest in structures created by arboreal ecosystem engineers. We observed, for the first time, ants using empty cocoons of the economically important silk moth species, Gonometa postica, as shelter and nesting sites. Individual trees and individual cocoons were occupied pr...
Article
Burrowing mammal disturbances often create heterogeneity within landscapes. Aardvark (Orycteropus afer) are extensive burrowers in sub-Saharan ecosystems and play an important role in structuring communities in arid environments. The burrowing activities of aardvark are often associated with heuweltjies (nutrient-rich mounds differing in soil and v...
Article
The richness of invasive alien plant species tends to decrease with increasing elevation. This pattern may be due to alien plant species requiring traits allowing survival at high elevations (the Abiotic Limitation Hypothesis; ALH). In contrast, the more recent Directional Ecological Filtering Hypothesis (DEFH) suggests that only species with broad...
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Aim: Biotic interactions have a central role in defining species assemblages, realized both through negative and positive impacts. However, forecasts of how these interactions affect biodiversity across landscapes are challenging (and lacking) because the outcome of interactions depends not only on the identity of the interacting species but also o...
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Biotic interactions may strongly affect the distribution of individual species and the resulting patterns of species richness. However, the impacts can vary depending on the species or taxa examined, suggesting that the influences of interactions on species distributions and diversity are not always straightforward and can be taxon-contingent. The...
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Background: Ectoparasites exhibit pronounced variation in life history characteristics such as time spent on the host and host range. Since contemporary species distribution (SD) modelling does not account for differences in life history, the accuracy of predictions of current and future species’ ranges could differ significantly between life histo...
Article
Marine plants are only incidentally included in conservation efforts for marine biodiversity. Here, for the first time, we apply phylogenetic methods to marine macrophytes (mangroves and seagrass species) to test for gaps in the current conservation network by identifying global diversity hotspots for these plant groups, and assess the degree to wh...
Article
The Arctic has experienced marked climatic differences between glacial and interglacial periods and is now subject to a rapidly warming climate. Knowledge of the effects of historical processes on current patterns of diversity may aid predictions of the responses of vegetation to future climate change. We aim to test whether plant species and genet...
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Full-text available
Biotic interactions are known to affect the composition of species assemblages via several mechanisms, such as competition and facilitation. However, most spatial models of species richness do not explicitly consider inter-specific interactions. Here, we test whether incorporating biotic interactions into high-resolution models alters predictions o...
Article
During recent decades large changes in vegetation biomass have been observed in arctic and alpine areas. While these temporal trends have been clearly linked to changing climatic conditions, the drivers of local spatial variation in biomass are still relatively poorly understood. Thus, we examine the effects of abiotic conditions (topography, soil...
Article
Can variation in the outcome of biotic interactions in relation to environmental severity be more accurately predicted when considering multiple stress and/or disturbance variables? The outcomes of biotic interactions are predicted to vary along environmental severity gradients. Using an observational approach, we demonstrate that explicitly consid...
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Early detection of emerging invasive plants depends on maximizing the probability of detecting new populations. Repeated surveys along a gradient of environmental conditions or in areas exposed to high propagule pressure provide a potentially efficient strategy for early detection of alien species. The long-term monitoring of such an area resulted...
Article
1. Biotic interactions exert considerable influence on the distribution of individual species and should, thus, strongly impact communities. Implementing biotic interactions in spatial models of community assembly is therefore essential for accurately modelling assemblage properties. However, this remains a challenge due to the difficulty of detect...
Article
Facilitative interactions are defined as positive effects of one species on another, but bidirectional feedbacks may be positive, neutral, or negative. Understanding the bidirectional nature of these interactions is a fundamental prerequisite for the assessment of the potential evolutionary consequences of facilitation. In a global study combining...
Article
QuestionsAre earth surface processes (ESPs) important determinants of species richness, composition and fine-scale distributions? Do different ESPs have similar effects on these vegetation characteristics? LocationSaana massif, northwest Finland (69 °N). Methods Vascular plant species occurrences, five environmental variables (related to soil condi...
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Full-text available
Biotic interactions are predicted to have the strongest influence on species assemblages in extreme environments. We therefore test the hypothesis that in abiotically-severe beaches plant–plant interactions, specifically facilitation, are important relative to abiotic conditions. This hypothesis is tested by assessing the influence of dominant vasc...
Article
AimTo quantify whether species distribution models (SDMs) can reliably forecast species distributions under observed climate change. In particular, to test whether the predictive ability of SDMs depends on species traits or the inclusion of land cover and soil type, and whether distributional changes at expanding range margins can be predicted accu...
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Extreme temperatures are key drivers controlling both biotic and abiotic processes, and may be strongly modified by topography and land cover. We modelled mean and extreme temperatures in northern Fennoscandia by combining digital elevation and land cover data with climate observations from northern Finland, Norway and Sweden. Multivariate partitio...
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Soil temperature and moisture are key determinants of abiotic and biotic processes in arctic-alpine regions. They are important links to understanding complex ecosystem dynamics under changing climate. The aims of this study were to (1) quantify fine-scale soil temperature and soil moisture variation, and (2) assess the influence of vegetation on s...
Article
Disturbances related to geomorphological processes are frequent, widespread and often intense at high latitudes and altitudes, affecting the fine-scale distribution of many plant species. While the inclusion of physical disturbances into models of species geographic ranges is widely recommended, no studies have yet tested the utility of field-quant...
Article
Shifts in precipitation regimes are an inherent component of climate change, but in low energy systems are often assumed to be less important than changes in temperature. Because soil moisture is the hydrological variable most proximally linked to plant performance during the growing season in arctic-alpine habitats, it may offer the most useful pe...
Article
Environmental conditions and plant size may both alter the outcome of inter-specific plant-plant interactions, with seedlings generally facilitated more strongly than larger individuals in stressful habitats. However, the combined impact of plant size and environmental severity on interactions is poorly understood. Here, we tested explicitly for th...
Article
Despite concerns about the richness of plant invaders on islands, and their likely effects on local systems, impacts of these species seem to be small. However, this may be due to an absence of information on impacts, including changing species occupancy and forecast occupancy, rather than lack of impact per se. Here we use the plant invaders on th...
Article
It is widely acknowledged that in the terrestrial Antarctic, interspecific interactions are typically unimportant in determining species distributions and community structure. Therefore, correlative models should prove useful for predicting current and future spatial variation in species abundance patterns. However, this idea has not been formally...
Data
Aim To describe and analyse the body size frequency distributions (BSFDs) of avian assemblages at several spatial scales in the Afrotropics. We also tested if the variation in median body size across assemblages at different spatial scales was related to environmental variables and whether purely stochastic processes could explain BSFDs. Location T...
Article
Studies of species range determinants have traditionally focused on abiotic variables (typically climatic conditions), and therefore the recent explicit consideration of biotic interactions represents an important advance in the field. While these studies clearly support the role of biotic interactions in shaping species distributions, most examine...
Article
Recent outbreaks of native bark beetles are unprecedented during the historical period. The aim of this manuscript is to develop a proxy-based methodology to infer past bark beetle outbreaks using lake sediments to provide long-term context for recent outbreaks. We test three hypotheses to determine how the ecological impacts of severe spruce beetl...
Article
Ecological theory suggests that positive plant—plant interactions can extend species distributions into areas that would otherwise be unfavourable. However, few studies have tested this hypothesis, and none have explicitly examined the associated prediction that inter-specific interactions between plants may broaden species altitudinal distribution...
Article
SUMMARY Habitat fragmentation can adversely impact biodiversity, although where remnant fragments of natural vegetation provide favourable conditions the negative effects of fragmentation may be mitigated. Host-parasite systems in fragmented areas have only recently been examined, with parasites generally showing higher prevalence and richness in f...
Article
Climate change leads to species range shifts and consequently to changes in diversity. For many systems, increases in diversity capacity have been forecast, with spare capacity to be taken up by a pool of weedy species moved around by humans. Few tests of this hypothesis have been undertaken, and in many temperate systems, climate change impacts ma...
Article
Climatic conditions and landscape features often strongly affect species' local distribution patterns, dispersal, reproduction and survival and may therefore have considerable impacts on species' fine-scale spatial genetic structure (SGS). In this study, we demonstrate the efficacy of combining fine-scale SGS analyses with isotropic and anisotropic...
Article
The acute thermal tolerance of ectotherms has been measured in a variety of ways; these include assays where organisms are shifted abruptly to stressful temperatures and assays where organisms experience temperatures that are ramped more slowly to stressful levels. Ramping assays are thought to be more relevant to natural conditions where sudden ab...