Avifaunal responses to environmental conditions and land-use changes in South Africa : diversity, composition and body size

Thesis (MSc)--University of Stellenbosch, 2007.ENGLISH ABSTRACT: In macroecology, body sizes in animal assemblages have traditionally been investigated from two perspectives: body size frequency distributions (BSFDs) and geographic variation in body size. Neither of these has been investigated for the South African avifauna; one objective of this study was therefore to explore these. The regional BSFD of South African birds was found to be right-skewed, as is usually found for assemblages at large scales. This suggests that mechanisms driving the shape of BSFDs elsewhere are also acting for the South African avifauna. The Southern African Bird Atlas database was used to calculate median body sizes of avian assemblages in quarter degree grid cells. Median sizes were then used to investigate geographic variation in body size across the country. Of the mechanisms previously proposed to explain geographic variation in body size, only the starvation resistance hypothesis, which states that large size confers starvation resistance during seasonally resource shortages, was supported, though weakly, as median body size decreased with increasing productivity. The ability of null models to predict the variation in body size was subsequently explored, and it was found that much of the variation in median size of assemblages could be predicted by randomly drawing species from the regional BSFD, particularly at high species richness values. This provides empirical support for a continuum between the dominance of niche-based processes (where assemblages are a product of organisms' response to their environment) at low richness and neutral processes (where organisms assemble at random) at higher richness. In addition, it emphasizes the need to consider null expectations in investigations of the geographic variation in size. The importance of the regional BSFD and species richness for body sizes of local assemblages is highlighted. Body size is one of several life history and community characteristics of animals that may be affected by anthropogenic disturbance to the environment. World-wide, landscapes are increasingly being altered by people, though few studies have investigated the effect of such disturbances on the avifauna of South Africa. The consequence of land-use changes on avian assemblages was therefore assessed in three South African regions which experience different environmental conditions and are threatened by different land-use changes. Birds were recorded in transects in undisturbed protected areas and the disturbed landscape outside the protected areas in the three regions. The effect of land-use change on avian assemblages varied between regions, and avian assemblages were most affected where disturbance was most intense. While species richness was not affected in a consistent manner across regions, species composition always changed in response to disturbance. This led to higher regional species richness as natural and disturbed areas supported different avian assemblages, and heterogeneity of assemblages between vegetation types usually became less pronounced in disturbed areas. Functional diversity was also compromised by land-use changes: the relative proportion of feeding guilds was altered, indicating that changes in food availability affect composition of assemblages. In contrast, mean body size of birds did not change in disturbed landscapes, which suggests that habitat architecture has little effect on body size. This study therefore highlights the importance of natural and protected areas for conserving species, assemblages and ecosystem processes.AFRIKAANSE OPSOMMING: In makro-ekologie is liggaamsgrootte van diergemeenskappe tradisioneel uit twee oogpunte ondersoek: liggaamsgrootte-frekwensieverspreidings (LGFVs) en geografiese variasie in liggaamsgrootte. Nie een van hierdie twee is al vir SuidAfrikaanse voels bepaal nie, en dit is dus 'n doel van hierdie studie om dit te ondersoek. Daar is gevind dat die land-wye LGFV 'n patroon van skuins na regs gewys het, soos gewwonlik die geval is vir diergemeenskappe op groat skaal. Prosesse wat die LGFV elders bepaal, is dus waarskynlik ook belangrik vir die LGFV van Suid-Afrikaanse voels. Die Suider Afrikaanse Voel Atlas is gebruik om die mediaan van die liggaamsgrootte van voelspesies in elke 15' x 15' vierkant te bepaal. Die waardes is gebruik om die geografiese variasie in liggaamsgrootte oor die hele land te ondersoek. Daar is al verskeie meganismes voorgestel wat geografiese variasie in liggaamsgrootte kan be"invloed. Hier is ondersteuning, alhoewel swak, gevind (liggaamsgrootte neem toe soos produktiwiteit afneem) vir die verhongeringweerstands hipotese, wat se dat groat liggaamsgrootte weerstand teen verhongering bied tydens tydperke van seisoenale tekortkominge. Daar is ook ondersoek hoe nulmodelle variasie in liggaamsgrootte kan voorspel, en daar is gevind dat baie van die variasie in liggaamsgrootte voorspel kon word deur spesies willekeurig vanuit die land-wye LGFV te kies. Dit was veral die geval vir gemeenskappe met hoe spesierykheid. Die resultate verskaf empiriese steun vir 'n kontinuum tussen nisgebaseerde prosesse (waar gemeenskappe ontstaan as gevolg van die manier hoe organismes op hulle omgewing reageer) wat by lae spesierykheid domineer, en neutrale prosesse (waar gemeenskappe willekeurig saamgestel word) wat by hoer spesierykheid domineer. Dit beklemtoon ook die noodsaakliheid van nul-modelle in die ondersoek van geografiese variasie in liggaamsgrootte, sowel as die belangrikheid van spesierykheid eri die grootskaalse LGFV vir liggaamsgroottes in plaaslike gemeenskappe. Liggaamsgrootte en ander kenmerke van dieregemeenskappe kan be'fnvloed word deur menslike steuringe aan die omgewing. Landskappe word wereldwyd al hoe meer deur mense verander. Daar bestaan tans min studies wat die invloed van hierdie antropogeniese steuringe op voels in Suid-Afrika bestudeer het. Die gevolge van landskapveranderinge vir voelgemeenskappe in drie Suid-Afrikaanse streke wat van mekaar verskil op grand van die omgewing en van landskapveranderinge is dus hier ondersoek. Voels is getel in natuurlike bewaarde gebiede en in versteurde areas buite die bewaringsgebiede. Die invloed van landskapveranderinge op voelgemeenskappe was verskillend in die drie streke, en die voelgemeenskappe is meeste geaffekter waar die landskapsteuring die meeste intens was. Terwyl spesierykheid nie op 'n konsekwente manier deur landskapveranderinge be'invloed is nie, het die samestelling van die gemeenskappe altyd verander. Die gemeenskappe in natuurlike en versteurde gebiede besit dus verskillende spesiesamestellings, wat tot hoer spesierykheid in die streke lei. Heterogeniteit in voelgemeenskappe tussen verskillende soorte vegetasie was meestal ook minder in versteurde as in natuurlike gebiede. Die funksionele diversiteit van voelgemeenskappe word boonop bedreig deur landskapveranderinge: in versteurde gebiede het die relatiewe proporsies van voedinggildes verander, wat aandui dat voedselbeskikbaarheid die samestelling van gemeenskappe affekteer, maar die gemiddelde grootte van voels het nie verander nie; die argitektuur van die omgewing het dus min invloed op die voels se . liggaamsgrootte. Die studie beklemtoon dus dat ongesteurde en bewaarde gebiede belangrik is om spesies, gemeenskappe en ekosisteemprosese te bewaar

Elephant rewilding affects landscape openness and fauna habitat across a 92-year period

Trophic rewilding aims to promote biodiverse self-sustaining ecosystems through the restoration of ecologically important taxa and the trophic interactions and cascades they propagate. How rewilding effects manifest across broad temporal scales will determine ecosystem states; however, our understanding of post-rewilding dynamics across longer time periods is limited. Here we show that the restoration of a megaherbivore, the African savannah elephant (Loxodonta africana), promotes landscape openness (i.e., various measures of vegetation composition/complexity) and modifies fauna habitat and that these effects continue to manifest up to 92 years after reintroduction. We conducted a space-for-time floristic survey and assessment of 17 habitat attributes (e.g., floristic diversity and cover, ground wood, tree hollows) across five comparable nature reserves in South African savannah, where elephants were reintroduced between 1927 and 2003, finding that elephant reintroduction time was positively correlated with landscape openness and some habitat attributes (e.g., large-sized tree hollows) but negatively associated with others (e.g., large-sized coarse woody debris). We then indexed elephant site occurrence between 2006 and 2018 using telemetry data and found positive associations between site occurrence and woody plant densities. Taken alongside the longer-term space-for-time survey, this suggests that elephants are attracted to dense vegetation in the short term and that this behavior increases landscape openness in the long term. Our results suggest that trophic rewilding with elephants helps promote a semi-open ecosystem structure of high importance for African biodiversity. More generally, our results suggest that megafauna restoration represents a promising tool to curb Earth's recent ecological losses and highlights the importance of considering long-term ecological responses when designing and managing rewilding projects

Opportunities for studying propagule pressure using gene flow reveal its role in accelerating biological invasions

When an alien species establishes at a new location, it must spread to become an invader. The extent to which propagule pressure promotes the spread of invaders, especially at local scales, is often difficult to quantify because it requires a reliable measure of, and variation in, rate of spread, and of propagule pressure across similar areas. In this issue of Molecular Ecology, Mairal et al. (2022) make use an unique system of paired sub-Antarctic islands, one with very infrequent human activities, and another inhabited by scientists, to assess the role of propagule pressure and anthropogenic disturbance in the introduction and spread of a major global invader, Poa annua L., to and on the islands. Genetic admixture between different genetic clusters is virtually absent from the little-visited island, while the inhabited island experienced more introduction events, but also significant admixture between genetic clusters. Detailed distribution maps of P. annua spanning more than 50 years allowed the authors to link genetic diversity to residence time. The nature of the system, and the multifaceted approach used by the authors, allows for new insights into the mechanism by which propagule pressure results in the spread of invasive species.Biodiversa ASICS.http://www.wileyonlinelibrary.com/journal/mechj2023Plant Production and Soil Scienc

Evolution of sociality in spiders leads to depleted genomic diversity at both population and species level

textcopyright 2017 John Wiley Sons Ltd.Across several animal taxa, the evolution of sociality involves a suite of characteristics, a "social syndrome," that includes cooperative breeding, reproductive skew, primary female-biased sex ratio, and the transition from outcrossing to inbreeding mating system, factors that are expected to reduce effective population size (Ne). This social syndrome may be favoured by short-term benefits but come with long-term costs, because the reduction in Ne amplifies loss of genetic diversity by genetic drift, ultimately restricting the potential of populations to respond to environmental change. To investigate the consequences of this social life form on genetic diversity, we used a comparative RAD-sequencing approach to estimate genomewide diversity in spider species that differ in level of sociality, reproductive skew and mating system. We analysed multiple populations of three independent sister-species pairs of social inbreeding and subsocial outcrossing Stegodyphus spiders, and a subsocial outgroup. Heterozygosity and within-population diversity were sixfold to 10-fold lower in social compared to subsocial species, and demographic modelling revealed a tenfold reduction in Ne of social populations. Species-wide genetic diversity depends on population divergence and the viability of genetic lineages. Population genomic patterns were consistent with high lineage turnover, which homogenizes the genetic structure that builds up between inbreeding populations, ultimately depleting genetic diversity at the species level. Indeed, species-wide genetic diversity of social species was 5-8 times lower than that of subsocial species. The repeated evolution of species with this social syndrome is associated with severe loss of genomewide diversity, likely to limit their evolutionary potential

What drives grassland-forest boundaries? Assessing fire and frost effects on tree seedling survival and architecture

1. Fire and frost represent two major hurdles for the persistence of trees in open grassy biomes and have both been proposed as drivers of grassland-forest boundaries in Africa. 2. We assess the response of young tree seedlings, which represent a vulnerable stage in tree recruitment, to traumatic fire and frost disturbances. 3. In a greenhouse experiment, we investigated how seedling traits predicted survival and resprouting ability in response to fire versus frost; we characterized survival strategies of seedlings in response to the two disturbances, and we documented how the architecture of surviving seedlings is affected by fire versus frost injury. 4. Survival rates were similar under both treatments. However, different species displayed different levels of sensitivity to fire and frost. Seedling survival was higher for older seedlings and seedlings with more basal leaves. Survivors of a fire event lost more biomass than the survivors of a frost event. However, the architecture of recovered fire- and frost-treated seedlings was mostly similar. Seedlings that recovered from fire and frost treatments were often shorter than those that had not been exposed to any disturbance, with multiple thin branches, which may increase vulnerability to the next frost or fire event. 5. Synthesis. Fire caused more severe aboveground damage compared with a single frost event, suggesting that fire is an important driver of tree distribution in these open grassland systems. However, the impact of repeated frost events may be equally severe and needs to be investigated. Also, woody species composition may be influenced by phenomena that affect the timing and frequency of seedling exposure to damage, as mortality was found to be dependent on seedling age. Therefore, changes in fire regime and climate are likely to result in changes in the composition and the structure of the woody components of these systems.The National Research Foundation and the University of the Witwatersrand, Johannesburg.http://www.ecolevol.orgpm2021Plant Production and Soil Scienc

COVID-19 and the academe in South Africa: Not business as usual

The famous R.E.M. song laments ‘It’s the end of the world as we know it, I had some time alone, I feel fine…’. Many South Africans would agree that COVID-19 signals the end of the world (or business) as we know it, and through the lockdown we have certainly had some time alone. But contrary to the lyrics, all may not be fine, especially for South Africa’s scientific community. The novel coronavirus SARS-CoV-2 has impacted every economic and social sector1 across the globe, including higher education in South Africa. Every student and staff member at a higher education institution will have been affected in some way and to varying degrees; not one person will emerge from this unscathed. It is impossible to predict every short- and long-term impact of the COVID-19 pandemic, but we will experience the aftershocks for a long time to come. Here we discuss some of these impacts, ranging from undergraduate level to large research projects, and we offer suggestions on how to mitigate some of the damage.Geograph

Molecular evidence for hybridization in the aquatic plant Limosella on sub-Antarctic Marion Island

DNA sequence data have become a crucial tool in assessing the relationship between morphological variation and genetic and taxonomic groups, including in the Antarctic biota. Morphologically distinct populations of submersed aquatic vascular plants were observed on sub-Antarctic Marion Island, potentially representing the two species of such plants listed in the island's flora, Limosella australis R.Br. (Scrophulariaceae) and Ranunculus moseleyi Hook.f. (Ranunculaceae). To confirm their taxonomic identity, we sequenced a nuclear locus (internal transcribed spacer; ITS) and two plastid loci (trnL-trnF, rps16) from three specimens collected on Marion Island and compared the sequences with those in public sequence databases. For all three loci, sequences from the Marion Island specimens were nearly identical despite morphological dissimilarity, and phylogenetic analyses resolved them to a position in Limosella. In phylogenetic trees and comparisons of species-specific sequence polymorphisms, the Marion Island specimens were closest to a clade comprising Limosella aquatica L., L. curdieana F.Muell. and L. major Diels for ITS and closest to L. australis for the plastid loci. Cytonuclear discordance suggests a history of hybridization or introgression, which may have consequences for morphological variability and ecological adaptation.The National Research Foundationhttp://journals.cambridge.org/action/displayJournal?jid=ANSam2022Plant Production and Soil Scienc

Spatial optimization of carbon-stocking projects across Africa integrating stocking potential with co-benefits and feasibility

Carbon offset projects through forestation are employed within the emissions trading framework to store carbon. Yet, information about the potential of landscapes to stock carbon, essential to the design of offset projects, is often lacking. Here, based on data on vegetation carbon, climate and soil, we quantify the potential for carbon storage in woody vegetation across tropical Africa. The ability of offset projects to produce co-benefits for ecosystems and people is then quantified. When co-benefits such as biodiversity conservation are considered, the top-ranked sites are sometimes different to sites selected purely for their carbon-stocking potential, although they still possess up to 92% of the latter carbon-stocking potential. This work provides the first continental-scale assessment of which areas may provide the greatest direct and indirect benefits from carbon storage reforestation projects at the smallest costs and risks, providing crucial information for prioritization of investments in carbon storage projects.http://www.nature.com/naturecommunicationshb201

Taxonomic homogenization and differentiation across Southern Ocean Islands differ among insects and vascular plants

CITATION: Shaw, J.D. et al. 2010. Taxonomic homogenization and differentiation across Southern Ocean Islands differ among insects and vascular plants. Journal of Biogeography, 37(2):217-228. doi:10.1111/j.1365-2699.2009.02204.xThe original publication is available at https://onlinelibrary.wiley.com/journal/13652699Aim: To investigate taxonomic homogenization and/or differentiation of insect and vascular plant assemblages across the Southern Ocean Islands (SOI), and how they differ with changing spatial extent and taxonomic resolution. Location: Twenty-two islands located across the Southern Ocean, further subdivided into five island biogeographical provinces. These islands are used because comprehensive data on both indigenous and non-indigenous insect and plant species are available. Methods: An existing database was updated, using newly published species records, identifying the indigenous and non-indigenous insect and vascular plant species recorded for each island. Homogenization and differentiation were measured using Jaccard’s index (JI) of similarity for assemblages across all islands on a pairwise basis, and for island pairs within each of the biogeographical provinces. The effects of taxonomic resolution (species, genus, family) and distance on levels of homogenization or differentiation were examined. To explore further the patterns of similarity among islands for each of the taxa and groupings (indigenous and non-indigenous), islands were clustered based on JI similarity matrices and using group averaging. Results: Across the SOI, insect assemblages have become homogenized (0.7% increase in similarity at species level) while plant assemblages have become differentiated at genus and species levels. Homogenization was recorded only when pairwise distances among islands exceeded 3000 km for insect assemblages, but distances had to exceed 10,000 km for plant assemblages. Widely distributed non-indigenous plant species tend to have wider distributions across the SOI than do their insect counterparts, and this is also true of the indigenous species. Main conclusions: Insect assemblages across the SOI have become homogenized as a consequence of the establishment of non-indigenous species, while plant assemblages have become more differentiated. The likely reason is that indigenous plant assemblages are more similar across the SOI than are insect assemblages, which show greater regionalization. Thus, although a suite of widespread, typically European, weedy, non-indigenous plant species has established on many islands, the outcome has largely been differentiation. Because further introductions of insects and vascular plants are probable as climates warm across the region, the patterns documented here are likely to change through time.Centre of Excellence for Invasion Biologyhttps://onlinelibrary.wiley.com/doi/10.1111/j.1365-2699.2009.02204.xPublisher’s versio

Incorporating biotic interactions in the distribution models of African wild silk moths (Gonometa species, Lasiocampidae) using different representations of modelled host tree distributions

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 interactions, in the form of host plant distributions, to increase model performance for two host‐dependent lepidopterans of economic interest, namely the African silk moth species, Gonometa postica and Gonometa rufobrunnea (Lasiocampidae). Both species are dependent on a small number of host tree species for the completion of their life cycle. We thus expected the host plant distribution to be an important predictor of Gonometa distributions. Model performance of a species distribution model trained only on abiotic predictors was compared to four species distribution models that additionally incorporated biotic interactions in the form of four different representations of host plant distributions as predictors. We found that incorporating the moth–host plant interactions improved G. rufobrunnea model performance for all representations of host plant distribution, while for G. postica model performance only improved for one representation of host plant distribution. The best performing representation of host plant distribution differed for the two Gonometa species. While these results suggest that incorporating biotic interactions into species distribution models can improve model performance, there is inconsistency in which representation of the host tree distribution best improves predictions. Therefore, the ability of biotic interactions to improve species distribution models may be context‐specific, even for species which have obligatory interactions with other organisms.The University of Pretoria (RDP funding to Michelle Greve), the South African National Research Foundation and the South African National Biodiversity Institute.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1442-99932018-12-01hj2018Plant Production and Soil Scienc