Current Projects

Bird pollination and anthropogenic influence

I am interested on how bird communities may disassemble in response to different pressures. For example, the effect of habitat fragmentation is becoming increasingly important as our urban areas expand. Fragmentation results in species-poor communities with specific nectar feeding birds lost in small urban fragments (Geerts and Pauw 2012 SAJB), including specialised pollinators in particular (Geerts and Pauw 2009 SAJB). Short-billed sunbirds are not substitutes, and fruit production could be increased by 35% in transformed landscapes if long-billed sunbirds are encouraged to return (and there are ways to do this!) (Geerts 2016 Plant Biology). In other research, I demonstrated that certain nectar feeding bird species avoid roads, and this challenges the idea that roadside verges act as biodiversity refugia and corridors in otherwise transformed landscapes (Geerts and Pauw 2011 Aust. Ecol.).

I am also interested in bee–bird pollinator competition and fire–pollinator interactions. Human-driven impacts in the natural Cape landscapes include elevated bee populations (via beekeeping) and increased fire frequencies. Bees largely compete for the same food source as nectar feeding birds. Although beekeeping has increased honeybee abundance far above natural levels, nectar-feeding birds were not consistently affected (Geerts and Pauw 2011 Population Ecology). Fire is a frequent disturbance in fynbos communities. I have a long-standing concern that increased fire frequency will lead to declining populations of the endemic and iconic Cape sugarbird, with cascading effects on dependant plant species. In a before–and–after fire study and a burnt–unburnt transplant study, birds visited flowers in the “before fire” and “unburnt” areas only. The results are surprising given the large number of bird-pollinated plants flowering in the early post-fire vegetation. Previously, this issued had received little consideration and I provided clear management guidelines (Geerts et al. 2012 Journal of Ornithology); specifically, fire managers should attempt to retain enough mature vegetation to prevent declines in Cape sugarbird numbers.

Plant and bird communities in Cape Fynbos

With the current global decline in pollinators, relationships between species interactions and diversity are becoming more important. If pollinator communities depend strongly on the diversity of flowering plants and vice versa, declines in the one will caused linked declines in the other. This topic of pollination communities has hardly been touched on, particularly so in Africa. I study the nectar-feeding bird pollinator community since the few consisting species aid in understanding the processes governing its assembly and disassembly. For plants I use the diverse Proteaceae family with its many bird dependant plants. On a small scale, nectar rather than vegetation structure or vegetation type is the most important predictor of the nectar-feeding bird community. On a larger scale ornithophilous Proteaceae abundance and species richness correlated significantly with the abundance and species richness of the nectar-feeding bird community. The addition of more than five ornithophilous Proteaceae species for each new nectar-feeding bird species, demonstrates an asymmetrical plant-pollinator relationship. The close association between plant and bird communities found in this study suggests an important role for community wide pollination mutualisms.

The Iingcungcu Project: Restoring pollinator migration routes

The Iingcungcu Project, a joint initiative of Stellenbosch University, CPUT and the City of Cape Town, aims to link the Table Mountain National Park with the Boland Mountains via a series of pollinator gardens that will act as fill stations for migrating sunbirds and sugarbirds crossing the Cape Flats.

Iingcungcu is a Xhosa word that means ‘long-billed birds’, or alternatively ‘royalty’. The impetus for the project came from the observation that nectar-feeding birds, particularly Malachite sunbirds, do not venture far into the urban areas that now surround the Table Mountain National Park and other smaller conservation areas on the Cape Flats. This is worrying, because nectar-feeding birds need to migrate in search of their shifting nectar resources, especially after fires. Such migration might occur within the Cape Peninsula, but when large areas of the Peninsula are burnt, birds may need to migrate across the city. In addition, populations of rare plants marooned in small conservation areas within the city may never get visited. Rondevlei is one such small urban conservation area that houses many rare plant species. The schools where gardens are now being established bridge the gap between Rondevlei and the nearby Muizenberg Mountain, part of the Tale Mountain National Park.

Learners are engaged in all aspects of the project. Activities such as planting, mapping, nectar measurement and the collection and analysis of bird census data integrate well into the Natural Sciences curriculum and offer the opportunity to teach concept such as pollination, community, sexual reproduction and dispersal, all without leaving the school grounds.

The project was initiated in 2014 by Bongani Mnisi as an MSc project under the supervision of Prof. Anton Pauw (SU) and myself (CPUT). Mnisi’s thesis reported preliminary evidence of an increase in the abundance of Cape white-eyes and Southern double-collared sunbirds at schools where gardens were planted, but the effects are still small. Malachite sunbirds were observed in the gardens for the first time in 2016. The effects on learners were more impressive, with significant increases in their knowledge of nature. The project is still in a very early stage. Mnisi has since completed his MSc and is now head of Nature Conservation for the City of Cape Town. The project is being run by Aaniyah Omardien and Ceinwen Smith, with a ten-year vision to grow this corridor right across the Cape Flats to the Stellenbosch Mountains.

http://academic.sun.ac.za/botzoo/iingcungcu/index.htm

https://www.facebook.com/Iingcungcu-sunbird-restoration-project-285157724989224/

Invasive alien plant species

A major anthropogenic influence are invasive alien plant species. Interactions with pollinators are thought to play a significant role in determining whether plant species may become invasive, and ecologically generalised species are predicted to be more likely to invade than more specialised species. To test this, colleagues and I assessed the floral biology and pollination ecology of N. glauca, which is a global invader. In regions where specialised bird pollinators are available, birds increase seed production. Surprisingly, in areas without pollinating birds, nectar resources are rarely exploited. We concluded that N. glauca is a successful invasive species, despite its specialised pollination system, because it has the phenotypic plasticity to become more frequently self-pollinating in foreign areas (Ollerton, Geerts et al. 2012). I expanded on this research theme by exploring the role of plant reproduction at the early stages of invasion and coupled this with the management aspect of emerging invasive plant species. This culminated in publications on emerging horticultural invasive plants (Le Roux et al 2010, Geerts et al. 2013 SAJB), floricultural species (Geerts et al. 2013 Austral Ecology) and species introduced for agriculture (Geerts et al. 2016 Biological Invasions).

A major aim of invasion ecology is to identify characteristics of successful invaders. Most plant groups that have been studied in detail (e.g. pines and acacias) have a high percentage of invasive taxa. Together with colleagues, we examined the global introduction history and invasion ecology of Proteaceae—a large plant family that have been widely disseminated by humans, but with few known invaders (Moodley, Geerts et al. 2013). This review highlighted that propagule pressure is the most important determinant of naturalization. While some traits showed a consistent influence at introduction, naturalization and invasion, others appear to only influence a single stage, and some have contrasting effects at different stages. Trait-based analyses therefore need to consider different invasion stages separately. As such there is considerable value in seeking the correlates and mechanisms underlying invasions for particular taxonomic or functional groups (Moodley, Geerts et al. 2014).

Threatened plant species and population projections models: Euryops virgatus

The second outcome of target three of the South African Strategy for Plant Conservation is focused on the monitoring of threatened plant species. The Custodians of Rare and Endangered Wildflowers (CREW) programme based at SANBI finds and monitors these species. Together with CREW we run a demographic monitoring project to collect more in-depth information about threatened species. Here we focus on the critically endangered Euryops virgatus B. Nord. (Asteraceae), known from only a single population. This population in Nieuwoudtville (Northern Cape Province, South Africa) has been monitored since 2009, by citizen scientists to enhance our understanding of its demography and ecology. Monitoring was conducted annually. Between 2009 and 2013 seedlings were absent and in 2014 the first record of seedlings was made. Seedling survival was assessed by constructing permanent plots; <15% of seedlings survived in the first year. Seedling dispersal distance was assessed and it was found that seeds do not disperse more than 1.5 m away from the parent plant. Seed banks, pollinators and selfing abilities were also assessed. Currently population projection models are constructed.

The effect of pollen limitation on population growth rates in a long-lived geophyte

An important question in plant ecology is whether elevated pollination levels translate into population growth rate and vice versa, whether depressed pollination levels lead to population declines. By combining plant demography and plant reproduction the population growth rate under different pollination scenarios can be predicted. This is particularly important for small and fragmented plant populations. In this study I focus on Brunsvigia orientalis, a geophytic, sunbird pollinated plant from the highly transformed Cape lowlands of South Africa. Pollinator intensity determines seed set in B. orientalis, but whether this is important for population growth remains untested. To calculate population growth rates, matrix models were constructed. By using population projection analyses, population fates under different pollination intensities are assessed. I show that the previously found link between pollination intensity and seed set can be extended to population growth rate, so that pollination intensity predicts population growth rate with a decline in the most pollen limited populations.

Fungi: Phytophthora

The genus Banksia (Proteaceae) is native to Australia and was introduced to South Africa in the late 1970s. Currently there are fourteen Banksia species grown in the Cape Floristic Region (CFR) for floriculture and horticulture. Of these fourteen species, B. ericifolia and B. integrifolia are invasive and another two species have naturalised. The remaining twelve species are classified as introduced species. Species traits and the environment, influence the differential abundance and Banksia species invasion status in the CFR. The aim of this study is to elucidate factors that may modulate differential abundance of Banksia species. A selective medium was used to isolate the phytopathogen Phytophthora cinnamomi ‘Rands’ (Oomycetes) from Banksias spp. soil samples and infected plant tissue. Fungal isolates were identified by employing morphological (light microscopy) and molecular (internal transcribing spacer) techniques. In order to probe the association between Banksia species antimicrobial activity and Banksia species invasion status, we conducted a minimum inhibitory concentration bioassay of twelve Banksia species against P. cinnamomi. The invasive B. ericifolia and B. integrifolia showed the highest antifungal activity and the introduced species B. hookeriana showed the highest antifungal activity against P. cinnamomi. A species may have morphological invasive traits like the naturalised B. speciosa but still be highly susceptible to phytopathogens. This study suggests that pathogens can act as barriers for a species to transition from an introduced species to be an invasive species

Other current projects:

Urban ecology

Restoration

Termite-aardwolf-antelope interactions

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