Department of Botany and Zoology

Permanent URI for this community

https://scholar.sun.ac.za/handle/10019.1/219

Browse

Now showing 1 - 9 of 9

The convergence and divergence of floral traits are driven by the heterogeneity of pollinator and plant communities
(Stellenbosch : Stellenbosch University, 2017-03) Newman, Ethan; Anderson, Bruce; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Substantial evidence suggests that pollinators are responsible for generating floral variation when they select upon floral traits involved in attraction as well the efficiency of pollen transfer. Another source of floral variation that is often neglected, is the role of community structure which drives floral divergence of traits involved in competition for the same pollinator resource. When these traits are selected upon across a heterogeneous landscape, it is thought to give rise to the formation of local floral forms which are often referred to as ecotypes. This thesis uses the long-proboscid fly (Prosoeca longipennis) study system as a platform for asking questions regarding the generation of floral variation. In my first data chapter (chapter two), I show how this variation can arise when tube length converges upon fly proboscis length across several localities, leading to a pattern of geographic trait matching. In addition, I also identify populations of species which appear to be morphologically divergent, because in populations where P. longipennis is absent, they are often pollinated by morphologically different pollinators. In chapter three, I investigate pollinator driven floral divergence in Nerine humilis, a species pollinated by long-proboscid flies in some populations and short proboscid insects in others. In this chapter, I demonstrate local adaptation of different floral forms associated with different pollinators. In addition, I take an extra step and demonstrate that the mechanical fit between flower and pollinator morphology is the mechanism behind local pollinator adaptation. In my fourth chapter, I show that floral adaptation may not always be as clearly illustrated as in chapter three, because most plants are visited by a multitude of functionally different pollinators. Here, I explore pollinator-mediated selection in Tritoniopsis revoluta and Nerine humilis with multiple functional pollinator types. Using single visitations, I demonstrate that flowers adapt to the optima and slopes of the additive fitness functions from all functional pollinator types. In my last data chapter, chapter five, I demonstrate how floral divergence may occur through the context of the floral guild community, where floral divergence does not occur through selection exerted by pollinators, but occurs as a result of competition for the placement of pollen on the bodies of long-proboscid fly’s across different localities. This resultant process of ecological character displacement gives rise to a pattern where mean style lengths of Pelargoniums are more different when they co-occur compared to when they occur on their own, where they may have style lengths that are similar or different to those in sympatry. This thesis contributes to the existing literature by providing much needed evidence on how selection exerted by pollinators as well as the structure of the floral guild community may drive adaptive divergence of floral morphology across a heterogeneous landscape.
Dispersal, dormancy, life history and breeding systems of southern African Asteraceae : risk-reducing strategies in unpredictable environments
(Stellenbosch : Stellenbosch University, 2015-04) De Waal, Caroli; Anderson, Bruce; Ellis, Allan G.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: How organisms respond to unpredictable environments is a fundamental question in evolutionary ecology. For example, plants may reduce the risk of reproductive failure by spreading their reproductive effort in space (dispersal) or in time (dormancy, iteroparity). Similarly, different plant breeding systems, (for example the ability to autonomously self-fertilise) may reduce the risk of reproductive failure in environments where pollination in particular is unreliable. Each of these strategies may be affected by selective pressures exerted by heterogeneous abiotic and biotic environments (e.g. unreliable rainfall patterns or range edge habitats). However, there is little theoretical or empirical consensus on how these strategies are related. In Chapter 2, I explore the association between dispersal and breeding system traits and range edge proximity. I show that annual daisies from Namaqualand, South Africa, are characterised by two discreet syndromes: high selfing ability associated with good dispersal and obligate outcrossing associated with lower dispersal, regardless of range position. This chapter illustrates that selection on both breeding system and dispersal traits may act consistently across distribution ranges. Because co-flowering plants often share pollinators, their fecundity is likely affected by changes in pollinator visitation rates or the transfer of conspecific relative to heterospecific pollen. In Chapter 3 I experimentally investigate the effects of con- and heterospecific density and spatial distribution pattern on pollination and fecundity in annual Namaqualand daisies. I show that increasing conspecific density and aggregation enhanced fecundity through increased mate availability and reduced heterospecific interference, independent of pollinator visitation rates. Moreover, I demonstrate the benefits of autonomous selfing when mates are limited and the potential for interspecific pollen transfer is high. In Chapter 4, I examine relative investment in dispersal vs. dormancy in seed heteromorphic Dimorphotheca (Asteraceae) species in relation to life history, rainfall unpredictability and range edge proximity. I show annuals and perennials differ significantly in the relative investment in different dispersal strategies. However, my findings provide little support for theoretical predictions of bet-hedging strategies in unpredictable or range edge habitats. This chapter emphasises the role of local environmental factors on fruit set that may obscure expected patterns across broad climatic gradients. Because of different costs and benefits of dispersal in space and time, we may expect negative patterns of covariation among dispersal and dormancy as alternative risk-reducing strategies. In Chapter 5, I provide evidence for a trade-off between these traits across 27 wind- dispersed daisy species from South Africa. This trade-off did not depend on life history effects, but was inconsistent at different levels of biological organisation. I also show that the effects of life history on spatial and temporal dispersal were inconsistent. Taken together, my research illustrates the importance of simultaneously investigating different risk-reducing strategies, because associations among them are clearly complex and often contradict theoretical expectations. Moreover I show that the effects of life history and phylogenetic relatedness cannot be disregarded. My findings underscore the importance of dispersal in space and time as well as autonomous selfing as risk-reducing responses to unreliable environments.
Diversity of the genus Seira (Collembola: Entomobryidae: Seirinae) in the Fynbos and Southern Afrotemperate forest
(Stellenbosch : Stellenbosch University, 2015-12) Liu, Wing Pui Amy; Anderson, Bruce; Chown, Steven L.; Jansen van Vuuren, Bettine; Janion-Scheepers, Charlene; Stellenbosch University. Faculty of Science. Dept of Botany and Zoology.
ENGLISH ABSTRACT: Soil is one of the most complex and understudied terrestrial habitats, and it comprises a wide range of organisms that affect the functioning of terrestrial ecosystems. Despite the importance of these below-ground fauna, our understanding of this diversity remains limited, especially in the Cape Floristic Region (CFR), where higher plants and other more conspicuous invertebrates have been better represented in the literatures. The main aim of this thesis is to provide the first insights into the taxonomic, cryptic and spatial diversity of one of the more diverse Collembola genera, Seira (Collembola: Entomobryidae: Seirinae), in the Fynbos and Southern Afrotemperate forest habitats of the CFR. Collembola constitute an important component of terrestrial biodiversity and are essential for ecosystem functioning. The thesis is divided into two data chapters. The first data chapter examines the mitochondrial barcoding COI (Cytochrome-c oxidase subunit I) gene of 496 Seira specimens from 41 Fynbos and forest sites. Discrete Molecular Operational Taxonomic Units (MOTUs) are identified within Seira. Furthermore, divergence times are estimated and tentatively used to propose historical triggers for the diversification of Seira. Habitat specificity of Seira is assessed through phylogenetic reconstruction using Parsimony and Bayesian analyses based on the nucleotide and amino acid sequences. Genetic divergence indicates that Seira is composed of at least 91 MOTUs, suggesting that morphological taxonomy has vastly under-estimated the richness of this genus by at least four folds. Most of the MOTUs are highly habitat specific and geographically localised. The reconstruction of an evolutionary time frame of these lineages reveals several deep diversifications in the Miocene and a spate of more recent radiations in the Pleistocene and Holocene. Palaeo-environmental fluctuations and vegetation composition shifts are hypothesised as having increased the environmental complexity of the region and this may have influenced the diversification patterns of Seira. In the second data chapter, the spatial variation of Seira diversity is examined and compared between and within two major habitat types, Fynbos and forest, across nine study sites. Abiotic variables were recorded and compared for the investigation of environmental differences among habitat types. The habitat specificity of Seira is assessed, as well as the relative effects of habitat types and study sites on assemblage structure. Species richness of Seira is higher in Fynbos than in forest, and this could be due to the high heterogeneity of niches and resources created by the steep environmental and floristic gradients in the Fynbos habitats. Perhaps one of the most striking results is the high levels of beta diversity exhibited by Seira. The spatial turnover of the Seira assemblage is complete or nearly complete among and within habitat types across study sites within the CFR. Low dispersal abilities and consequently isolated evolutionary histories may account for the strong assemblage differences within the same habitat type of different study sites. However, the substantial differences in assemblage composition between adjacent habitat types in the same site are likely to be the result of the contrasting abiotic conditions exhibited by the Fynbos and forest habitats, as found by this study. Overall, the results of this thesis suggest that Seira species richness is much greater than previously thought. It follows similar diversity patterns to the well-described and hyper-diverse plant communities of the CFR. Here, for both CFR plants and Seira, the spectacular regional diversity displayed is not the result of high alpha diversity, but rather of substantial beta diversity. Because of the high beta diversity and the fact that only two CFR vegetation types were sampled from a limited number of study sites, I predict that the Seira species richness presented here is but the tip of the iceberg.
Evolutionary drivers of temporal and spatial host use patterns in restio leafhoppers Cephalelini (Cicadellidae)
(Stellenbosch : Stellenbosch University, 2015-12) Augustyn, Willem Johannes; Ellis, Allan G.; Anderson, Bruce; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: Understanding how divergent selection results in the evolution of reproductive isolation (i.e. speciation) is an important goal in evolutionary biology. Populations of herbivorous insects using different host plant species can experience divergent selection from multiple selective pressures which can rapidly lead to speciation. Restio leafhoppers are a group of herbivorous insect species occurring within the Cape Floristic Region (CFR) of South Africa. They are specialised on different plant species in the Restionaceae family. Throughout my thesis I investigated how bottom-up (i.e. plant chemistry/morphology of host plant species) and top-down (i.e. predation and competition) factors drive specialisation and divergence in restio leafhoppers. I also investigated interspecific competition as an important determinant of restio leafhopper community structure. In chapter 2 I quantified host specificity of restio leafhopper species within a local community for 24 months. I found that restio leafhopper species are highly host specific and potentially synchronised with the growth phases of their host plants. In chapter 3 I used a network metric, modularity, to determine whether host plant partitioning in a restio leafhopper community is non-random (i.e. driven by a deterministic process). This metric allows the identification of the components underlying host plant partitioning (modules). I then performed experiments to show that modules, and therefore host plant partitioning, can mostly be explained by preference and performance relationships (i.e. bottom-up factors). In chapter 4 I used null models to test whether niche partitioning in restio leafhopper communities is a general pattern across the landscape. I found non-random niche partitioning, which results from strong host specificity, in all investigated restio leafhopper communities. In addition, I performed binary host choice experiments in the presence and absence of interspecific competition, but found no evidence that interspecific competition narrows host preferences. These findings suggest that host specificity, the cause of niche partitioning, is likely shaped over evolutionary time. Sampling multiple interaction networks across the CFR, in chapter 5, I tested whether restio leafhopper populations are more host specific in species rich communities and regions in the CFR than in species poor communities and regions. I found no positive relationship between restio leafhopper species richness and host specificity at any scale. These findings suggest that specialisation is not driven by interspecific competition. In chapter 6 I investigated host shifts in Cephalelus uncinatus. C. uncinatus has a broader distribution than any single restio species that it can use; suggesting that host plant related divergence may result from geographic range expansion. I found that allopatric and parapatric populations, but not sympatric individuals, using different host plants have divergent host preferences. I also found evidence for morphological divergence in traits related to predator avoidance in population pairs that exhibit divergent host preferences. My findings emphasise the importance of both bottom-up and top-down factors, with the exception of interspecific competition, as determinants of specialisation and divergence in restio leafhoppers. I find no evidence that interspecific competition is an important force structuring restio leafhopper communities. Instead, strongly niche partitioned community structure appears to emerge from the speciation process.
Novel insights into pollen movement and floral evolution revealed by quantum dots
(Stellenbosch : Stellenbosch University, 2018-12) Minnaar, Corneile; Anderson, Bruce; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: To understand the evolution of flowers and mating systems in animal-pollinated plants, we have to directly address the primary function for which flowers evolved—the movement of pollen from anthers to stigmas. Yet, despite a long and distinguished history of making significant advances in understanding of natural selection and evolution, the field of pollination biology has largely studied pollen movement indirectly (e.g., pollen analogues or paternity assignment to seeds) due to a lack of suitable pollen tracking methods. Consequently, understanding of pollen export mechanisms and male reproductive strategies has been limited. In Chapter 2, I describe and test a novel technique to label and track the movement of pollen grains using quantum dots. I show that quantum dots can be attached to pollen grains of several different species and that their attachment to pollen appears not to affect pollen dispersal. In Chapter 3 I employ quantum dot pollen-labelling to test the placement and transfer of pollen in a unique population of Lapeirousia anceps (Iridaceae) with a bimodal distribution in floral tube length. I find that floral-tube length acts as a strong reproductive isolation barrier between plants with short-tubed flowers and longtubed flowers. In Chapter 4 I use quantum dots to explore the function of floral handedness in Wachendorfia paniculata. Based on pollen transfer experiments, pollen moves predominantly between left- and right-handed flowers, rather than between flowers of the same type. These experiments allowed the creation of the first map of anther-level pollen grain placement on the bodies of bees. Pollen placement maps revealed pollen quality heterogeneity across pollinator bodies, and that stigmas of W. paniculata aligned with areas on bee bodies where the capture of outcrossed pollen is most likely. This led to greater than expected outcross pollen movement. These findings underline the importance of studying micro-scale pollen landscape composition on pollinator bodies and how stigmas interact with them. The thesis concludes with a review which assesses the history of studying male function in plants and identifies critical gaps in our understanding of the ecology and evolution of pollen transport. I explore male reproductive function along the male fitness pathway, from pollen production to ovule fertilization. At each step of the pathway to paternity, I discuss evolutionary options to overcome barriers to siring success. In particular, I highlight a newly emerging idea that bodies of pollinators function as a dynamic arena facilitating intense male–male competition, where pollen of rival males is constantly covered or displaced by competitors. This perspective extends the pollen-competitive arena beyond the confines of the stigma and style, and highlights the opportunity for important new breakthroughs in the study of male reproductive strategies and floral evolution.
Pollinator-driven floral variation in Tritoniopsis revoluta
(Stellenbosch : University of Stellenbosch, 2010-03) Ros, Petra; Anderson, Bruce; Ellis, Allan G.; University of Stellenbosch. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: It is thought that a large proportion of the great variety of floral structures in flowering plants reflect adaptations to different biotic pollen vectors. Divergence in flower traits and pollinators is linked to speciation. Pollinator-driven speciation is thought to have played a large role in the spectacular floral diversity found in South African Iridaceae and the genus Tritoniopsis is a particularly good example of this. This study focuses on Tritoniopsis revoluta, a pink irid occurring in the Swartberg and Langeberg Mountains, as well as Potberg Mountain. I tested the hypothesis that variation in flower tube-lengths of Tritoniopsis revoluta are related to the geographic distribution of pollinators and the variation of their tongue lengths. It was determined that this species is highly variable in respect to corolla tube-length and is pollinated by different fly species across its range. Also, the tongue-lengths of the fly pollinators corresponded almost exactly with the tube-length of the flowers they were pollinating in each population. In some populations, where long-proboscid flies were absent, bees were observed visiting T. revoluta flowers. This presents evidence for pollinator-driven floral variation within a single plant species, and most of this vast diversification in floral morphology has probably been driven by morphological variation found within a single fly family. In one population I found variable tube-lengths which appeared to exhibit a bimodal distribution of corolla tubelengths. I hypothesized that the two Tritoniopsis revoluta ecotypes at this population are pollinated by two different pollinators, leading to assortative mating, and ultimately strong inter-ecotype incompatibility. Tritoniopsis revoluta is self-incompatible and exists as two discrete entities (morphotypes) at the Gysmanshoek Pass site, and these entities differ in tubelength, color, nectar volume and sugar content. These morphotypes were not pollinated by long-proboscid flies, but seems to represent a recent shift to pollination by Amegilla bees. However, ecotypes are not reproductively isolated as short and long flowers can produce offspring, rather tube-length differences are possibly maintained through spatial separation. To compliment the correlatory data between flower tube-lengths and pollinator tongue-lengths, I used molecular tools (chloroplast markers and AFLPs) to elucidate the patterns of tube-length evolution in Tritoniopsis revoluta. I aimed to determine the directionality and frequency of transitions between tube-length categories. Tube-length transitions would be suggestive of flower morphology being labile, and together with the tube-tongue length correlation it suggests pollinator shifts may drive the changes in tube length. Character state reconstructions using tube-length as character determined that four evolutionary transitions to shorter tube-length categories and two transitions to longer categories occurred. I also tested whether morphological divergence between populations corresponds to patterns of divergence from neutral genetic markers. Population genetic structure in this system showed that the different populations of T. revoluta are vicariant and tube-length differences between them could have evolved through selection.
Rodents and restios : rodents and the fates of Willdenowia incurvata (Restionaceae) seeds
(Stellenbosch : Stellenbosch University, 2017-03) Weighill, Benjamin; Anderson, Bruce; Wossler, Theresa; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH SUMMARY: The biodiversity hotspot of the fynbos offers a “natural laboratory” to study species diversification, particularly in flowering plants. Often it is the interactions with the surrounding biotic or abiotic environments that drive this diversification. Interactions between plants and seed dispersers are just one of these interactions. In Chapter 1 of this thesis, recent studies pertaining to rodent assisted seed dispersal as well as other biotic seed dispersers in the fynbos were reviewed. This review emphasized the need for more studies of biotic seed dispersal in the fynbos despite the recent discovery of the first dung beetle assisted seed dispersal in the fynbos and the first investigations into seed dispersal by the Cape spiny mouse (Acomys subspinosus) and the hairy-footed gerbil (Gerbilliscus paeba). In Chapter 2, the seed dispersing and consumption behaviour of the hairy-footed gerbil (Gerbilliscus paeba) and the four-striped mouse (Rhabdomys pumilio) was investigated. It was confirmed that G. paeba dispersed seeds of Willdenowia incurvata (Restionaceae) at night and only consumed a small percentage of seeds in situ. In contrast, R. pumilio, which was only active during the day, only consumed and never dispersed seeds. In Chapter 3, the final data chapter, the effect of added elaiosomes from the closely related Willdenowia glomerata on rodents’ reactions to W. incurvata seeds was investigated. It was found that the added elaiosomes deterred both G. paeba and R. pumilio from interacting with seeds of W. incurvata. Both rodent species preferred seeds without elaiosomes attached. Gerbilliscus paeba consumed and dispersed more seeds without elaiosomes attached than seeds that had elaiosomes attached when given a choice between seeds the two seed treatments. Rhabdomys pumilio, which does not disperse seeds, also consumed more seeds without elaiosomes attached than seeds with elaiosomes attached. In the fynbos, one of the prevailing views regarding myrmecochory (seed dispersal by ants) is that it evolved as a response to heavy seed predation by rodents as seeds are rapidly removed from the soil surface by ants. However, the findings of this thesis suggest that not all rodents are purely seed predators and that some species may play an important role in seed dispersal. Consequently, it is more likely that myrmecochory evolved primarily to protect seeds from fire, through seed burial. Seed dispersal by rodents also involves burial and so it is likely that some rodents may perform a similar role to ants in protecting seeds from fire. From a biodiversity perspective, the further study and identification of new interactions of this kind are key in understanding the processes that shaped the diversity seen in the fynbos today. In addition, such interactions are critical for maintaining ecosystem function. Protection of this biodiversity hotspot becomes extremely challenging when species interactions are unidentified or unstudied, emphasizing the importance of this study for conservation efforts. From an evolutionary ecology perspective, how scatter-hoarding in rodents evolved, as well as the evolution of plant strategies that enhance dispersal by rodents are highly contested. Evidence from fynbos studies could provide further insights for drawing conclusions regarding the evolution of this plant-animal interaction.
Scatter-hoarding in Acomys subspinosus : the roles of seed traits, seasonality and cache retrieval
(Stellenbosch : Stellenbosch University, 2011-12) Rusch, Ursina Denise; Anderson, Bruce; Midgley, Jeremy; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: With growing concerns about current environmental issues, such as climate change, that affect ecosystems around the world, understanding ecosystem function is becoming increasingly important. In this study, I investigate the plant – seed disperser mutualism between an endemic scatter-hoarding mouse Acomys subspinosus and its Proteaceae plant counterpart Leucadendron sessile in the biodiversity hotspot of the Cape Floristic Region, South Africa. The main objective of this thesis is to investigate the seed selection and caching behaviour of A. subspinosus. First, I determined the seed selection strategy for dispersal and burial by A. subspinosus. Acomys subspinosus may exert stabilizing selection pressure onto L. sessile seeds by dispersing and burying medium seeds with medium hull-thicknesses. Small seeds were eaten in situ and large seeds left at depots. I concluded that the buried L. sessile seeds may have a competitive advantage when it comes to seedling establishment in a post-fire environment, since seeds dispersed by rodents in the fynbos, such as L. sessile, are much larger in size and therefore have more stored nutrients and rapid growth capabilities than seeds dispersed by other vectors. Secondly, I documented rodent dispersal behaviour over a full years’ time. Acomys subspinosus dispersal behaviour changed significantly over the seasons, which I attributed to a change in food availability as the year progressed. Acomys subspinosus buried seeds in autumn after mass seed drop but began to recover caches and consume seeds during winter and spring. The rodent switched to an insectivorous diet in spring. I propose that the A. subspinosus – L. sessile relationship is mutualistic during the year, but the relationship does shift in the favour of the rodent during winter and spring. Lastly, I address the scatter-hoarding behaviour of A. subspinosus and cache recovery ability of its assumed closest food competitor Rhabdomys pumilio. I found that cache size has a profound influence on pilferage rates of L. sessile seeds. Acomys subspinosus scatter-hoarded the majority of seeds singly in the field and R. pumilio had difficulties finding those single-cached seeds in dry substrate under controlled experimental conditions, serving as evidence that scatter-hoarding is an effective method of pilferage mitigation by A. subspinosus during the dry summer months. Relatively little was known about this plant – disperser mutualism and how it functions before this thesis were conducted. I have provided insights into the influence of rodent disperser behaviour on seed morphology development, seed fate and seed persistence in the field and suspect that the plant –disperser relationship may have a larger influence on ecosystem dynamics than previously anticipated. Further research on this system is of importance, especially with today’s emerging environmental instability and human interference that threaten the robustness of highly interconnected ecosystems like the fynbos.
Spatial reproductive separation in a handed flower: variation across space and time
(Stellenbosch : Stellenbosch University, 2021-12) De Kock, Celeste; Anderson, Bruce; Minnaar, Corneile; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
ENGLISH ABSTRACT: In many angiosperms, pollinator-driven selection has led to adaptive radiation, spe- cialisation and phenotypic variation over space and time. Most specialised floral adaptations function by improving the efficiency of cross-pollination, while also lim- iting or delaying the chances of self-pollination. This study focuses on the variation of the distances between reproductive parts in Wachendorfia paniculata, an enan- tiostylous geophyte that occurs predominantly in the Western Cape, South Africa. Wachendorfia paniculata displays geographic variation in reproductive separation between populations, as well as temporal variation facilitated by floral movement over time within populations. In Chapter 2, I investigated whether geographic vari- ation in the separation between reproductive parts corresponded with shifts in pol- linator environments between populations, and whether floral movement has any functional significance during pollination. I expected that upper anther-stigma dis- tance would decrease in populations where large pollinators were scarce or absent, whilst lower anther distances were expected to remain relatively similar. Within each population, I recorded reproductive separation distances, pollinator visitation rates, abundances and wingspans, which varied significantly between study sites. Surpris- ingly, large pollinators appeared unimportant in the present pollinator landscape. Even though the mean weighted wingspan of pollinators in a population did not pre- dict the degree of reproductive separation, honeybee visitation rate was negatively correlated with the distance between the lower anthers, suggesting that frequent vis- its by small pollinators might select for narrower distances. I also found that floral movement contributed to the observed variation by reducing the distance between reproductive parts throughout the day. These findings prompted me to investigate whether floral movement could be beneficial in populations that are dominated by small pollinators in Chapter 3. Here, I explored the functional significance of floral movement by recording floral narrowing for the duration of anthesis in a single pop- ulation. I hypothesised that floral narrowing acts as a mechanism of reproductive assurance by increasing the likelihood of pollinators making contact with the stigma and/or anthers later in the day. I measured the lateral and vertical reproductive separation distances hourly and presented virgin donor and recipient inflorescences to honey bees to record how pollen deposition and receipt rates changed with flo- ral narrowing. Floral movement was substantial and highly variable, especially for anther-stigma narrowing. The likelihood of stigmatic pollen receipt did not change with time or floral narrowing, and was dependent on the density of pollen on bee wings. I propose that floral movement might act as a reproductive assurance strat- egy when large pollinators are absent or when pollinator visitation rates are low. I argue that stigmatic movement is the result of a trade-off between receiving high quality pollen and getting pollinated: stigmas are positioned to receive high qual- ity pollen in the morning, but they shift to positions that maximize the chances of pollen receipt later in the day. While lower anther movement was not as noticeable as stigmatic movement, lower anthers were more likely to deposit pollen on pollina- tors at smaller separation distances. I conclude that the variation in reproductive separation at spatial and temporal scales is likely to be influenced by multiple biotic and abiotic factors, but that pollinator availability could still play an important part in shaping the floral morphology of W. paniculata. Key words: Geographic variation; Floral movement; Herkogamy; Enantiostyly; Pollinator adap- tation

Browse

Browsing Department of Botany and Zoology by browse.metadata.advisor "Anderson, Bruce"

Results Per Page

Sort Options