Nectar distribution and nectarivorous bird foraging behaviour at different spatial scales

Coetzee, Anina (2016-03)

Thesis (PhD)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: While foraging strategies of animals may be shaped by the distribution of their food resources, these strategies in turn also affect the ecology and evolution of their resources. In this regard, African systems, of all the different bird-pollination systems worldwide, have been least studied. I investigated the relationships between these aspects at population, community and landscape levels in the bird-pollination systems of the Cape Floristic Region. This biodiversity hotspot in the southwest of South Africa contains an unusually high number of bird-pollinated plant species relative to the number of pollinating bird species. Chapter 2 describes how I experimentally tested which nectar resource traits affect sunbird foraging behaviour at the small scale within populations. Sunbirds’ behaviour was largely determined by visual signals and distances between nectar resources. The birds showed flower colour preferences, but no flower constancy (selective foraging only on one flower type). The foraging behaviour of pollinators seems to influence plant community assembly. With the use of null models, I show in Chapter 3 that communities of Proteaceae, a diverse and dominant plant family in the Cape Floristic Region, are structured both by competition for and facilitation of pollination. This was deduced from the non-random structure of the plant communities with respect to pollination syndromes and style lengths, which are proxies of the degree of pollinator sharing and of interspecific pollen transfer. While species traits were important driving forces of community assembly in natural habitat, I show in Chapter 4 that species and habitat traits may also be important factors structuring bird communities in novel environments such as human settlements. Through a questionnaire, I determined how well different species of nectarivorous birds are adjusting to urban environments and which traits facilitate and prevent this adjustment. Nectar-generalist birds were successful exploiters of urban resources and were most abundant in gardens with large vegetated areas, bird baths and feeders. Nectar-specialist birds were less successful at adjusting, due to their high dependence on nectar. The presence of sugar water feeders and the number of indigenous bird-pollinated plants in gardens best predicted the communities of nectar-specialist birds. All nectarivorous birds were negatively affected by dispersal barriers. Lastly, in Chapter 5, I use biome-wide atlas databases for birds and proteas to show how nectar distribution affects bird abundances at a landscape scale. The non-significantly different flowering phenology patterns throughout the biome suggest that nectarivorous birds would not need to migrate seasonally. Instead, birds may be sustained within mountain ranges all year round by the complementary flowering of species of different genera. Low floral abundances in the dry months of the year may still produce resource bottlenecks and this may encourage birds to forage in areas of human settlement. Though we have gained insight into some of the relationships between African nectarivorous birds and their nectar resource distributions in space and time, there is still much to learn. There is also an urgent need to understand the effects of land-use change on the long-term persistence of nectar-feeding birds of the Cape Floristic Region.

AFRIKAANSE OPSOMMING: Die voedingsstrategieë van diere kan gefatsoeneer word deur die verspreiding van hul voedselbronne, maar terselfdertyd kan hierdie strategieë die ekologie en evolusie van hul voedselbronne affekteer. In hierdie opsig is Afrika sisteme, van al die verskillende voëlbestuiwingssisteme wêreldwyd, die minste bestudeer. Ek het die verhoudings tussen hierdie aspekte in die voëlbestuiwingsisteme van die Kaapse Blommeryk op populasie-, gemeenskaps- en landskapsvlak ondersoek. Hierdie biodiversiteit-brandpunt in die suid-weste van Suid-Afrika huisves ‘n ongewone groot aantal voëlbestuifde plantspesies teenoor die aantal voëlbestuiwerspesies. Hoofstuk 2 beskryf hoe ek eksperimenteel getoets het watter nektarbroneienskappe die voedingsgedrag van suikerbekkies op klein skaal binne populasies affekteer. Suikerbekkies se gedrag is grootendeels bepaal deur visuele seine en die afstande tussen nektarbronne. Die voëls het blomkleurvoorkeure getoon, maar nie blomkonstantheid (selektiewe voeding op een blomtipe) nie. Die voedingsgedrag van bestuiwers blyk plantgemeenskapsamestelling te affekteer. Met die gebruik van nulmodelle, wys ek in Hoofstuk 3 dat gemeenskappe van Proteaceae, ‘n dominante plantfamilie in die Kaapse Blommeryk, deur beide kompetisie vir en fasilitering van bestuiwing gestruktureer word. Dit is afgelei uit die nie-ewekansige struktuur van plantgemeenskappe met betrekking tot bestuiwingsindrome en styllengtes, wat ‘n maatstaf is van interspesifieke stuifmeeloordrag en die mate waartoe plante bestuiwers deel. Terwyl spesies-eienskappe belangrike dryfkragte was in gemeenskapsamestelling in natuurlike habitat, wys ek in Hoofstuk 4 dat spesie- en habitateienskappe ook belangrike faktore kan wees in die strukturering van voëlgemeenskappe in nuwe omgewings soos menslike nedersettings. Ek het deur ‘n vraelys bepaal hoe goed nektarvretende voëls in stedelike omgewings aanpas en watter eienskappe hierdie aanpassing fasiliteer of verhoed. Nie-spesialis nektarvretende voëls was suksesvolle uitbuiters van stedelike bronne en was die volopste in tuine met groot beplante areas, voëlbaddens en -voerders. Nektarspesialis voëls het minder suksevol aangepas, weens hul hoë afhanklikheid van nektar. Die teenwoordigheid van suikerwatervoerders en die aantal inheemse voëlbestuifde plante in tuine was die belangrikste bepalers van nektarspesialis voëlgemeenskappe. Alle nektarvretende voëls was negatief geaffekteer deur verspreidingshindernisse. Laastens gebruik ek in Hoofstuk 5 bioomwye atlasdatabasisse van voëls en proteas om te wys hoe nektarverspreiding voëlgetalle op die landskapsvlak affekteer. Die nie-beduidende verskille in blombloeiingspatrone regdeur die bioom suggereer dat nektarvretende voëls nie seisoenaal hoef te migreer nie. Voëls kan regdeur die jaar binne bergreekse onderhou word deur komplimentêre bloeipatrone van spesies van verskillende genera. Die lae getal blomme in die droeë maande van die jaar kan steeds voedselbronbottelnekke veroorsaak en dit mag dalk voëls aanmoedig om in menslike nedersettings voedsel te soek. Alhoewel ons insig oor die sommige van die verhoudings tussen Afrika nektarvretende voëls en die verspreiding van hul nektarbronne in tyd en ruimte gegroei het, is daar steeds baie om te leer. Daar is ook ‘n dringende behoefte om die effek van veranderings in landgebruik op die langtermyn-voortbestaan van nektarvretende voëls van die Kaapse Blommeryk te verstaan.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98825
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