Amy-Leigh Wilson

Seed production in a threatened Aloe is not affected by bird exclusion or population size

Small populations of many plant species have been shown to exhibit ecological Allee effects. These effects are expected to be pronounced in plants which are obligate outcrossers and rely on pollinators which forage preferentially in larger populations with greater nectar availability. We examined the breeding and pollination systems, level of pollen limitation and seed production in populations of a threatened “ornithophilous” species, Aloe pruinosa. Experimental hand-pollinations showed that A. pruinosa is genetically self-incompatible and thus an obligate outcrosser. Experimental exclusion of birds from inflorescences did not affect seed production, suggesting that insects are effective pollinators. Supplemental hand-pollinations in several populations showed that seed production in A. pruinosa is not pollen limited. Further, there were no significant relationships between population size and any measure of reproductive success in this Aloe species. Small populations of A. pruinosa are thus viable in terms of pollination processes and should be protected from more direct threats, such as habitat alteration.

Food preferences of Knysna and purple-crested turacos fed varying concentrations of equicaloric and equimolar artificial fruit.

SUMMARY The effects that different fruit sugar types and concentrations have on food preferences of avian frugivores have been relatively poorly studied. Although it has been recently advocated that preference is based on equicaloric energy it is also important to note whether preferences change as energy content changes. Therefore, sugar preferences of equicaloric and equimolar artificial fruit of different sugar types at varying concentrations and molarities were investigated in two relatively large South African frugivores, Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos. Artificial fruits containing 6.6, 12.4 or 22% sucrose or glucose, and artificial fruits containing 0.42, 0.83 or 1.66 mol l–1 sucrose or glucose, were used to determine sugar preferences. Knysna turacos preferred the sucrose to the glucose equicaloric artificial fruit diet at low concentrations whereas purple-crested turacos showed no preference for either diet. Both turacos species preferred the sucrose equimolar artificial fruit diet to the glucose at low concentrations. At high concentrations neither species showed a preference for either equicaloric or equimolar artificial fruit diets. This suggests that energy requirements influence food preferences more than sugar type and that birds will select fruit that is higher in energy irrespective of sugar type. This complements an earlier study on digestion of differing equicaloric and equimolar artificial fruit sugar types. It again emphasizes the need for future studies looking at the composition of indigenous forest fruit sugars in order to obtain insight into the role of these avian frugivores as potential seed dispersers of fruiting tree species.

Digestive efficiency of Knysna and purple-crested turacos fed varying concentrations of equicaloric and equimolar artificial fruit

SUMMARY Avian frugivores have been somewhat poorly studied with regards to the effects that different fruit sugar types and concentrations have on their digestive efficiencies. Therefore, two relatively large South African frugivores, the Knysna turaco (Tauraco corythaix) and the purple-crested turaco (Gallirex porphyreolophus), were fed artificial fruit that contained equicaloric and equimolar concentrations of different sugars, to determine their daily food and energy intake, digestive efficiencies and digestive transit times. The artificial fruit contained 6.6, 12.4 or 22%, or 0.42, 0.83 or 1.66 mol l–1 sucrose or glucose. Food intake of both turaco species increased with decreasing sugar concentration and molarity, irrespective of sugar type, suggesting compensatory mechanisms for energy requirements. Apparent assimilation efficiencies of both turaco species ranged from 61.4-90.0% and 60.2-92.4% for equicaloric and equimolar artificial fruit diets, respectively. Digestive transit times for both turaco species were slowed with an increase in sugar concentration and molarity, irrespective of sugar type. Consequently these two frugivores appear to be tolerant of sugar type and would be expected to select fruits based on energy yields. Future studies of the composition of indigenous forest fruit sugars may give insight into food preferences of the turaco species and their role as potential seed dispersers of fruiting tree species.

Ingestion by an invasive parakeet species reduces germination success of invasive alien plants relative to ingestion by indigenous turaco species in South Africa

Avian frugivores play a key role in seed dispersal of many plant species, including invasive alien plants. We assessed the effect of gut passage on the germination of selected invasive alien plant species in South Africa. Fruits of four fleshly-fruited invasive alien plant species: Solanum mauritianum, Cinnamomum camphora, Psidium guajava, and Morus alba, were fed to two species of indigenous turacos, Knysna (Tauraco corythaix) and purple-crested (Gallirex porphyreolophus) turacos, and to invasive rose-ringed parakeets (Psittacula krameri). Seed retention time was determined as this can influence both seed dispersal and germination success. Germination success of ingested seeds was compared with that of manually de-pulped seeds, as well as to seeds in whole fruit. The germination success of seeds of all the invasive plant species increased significantly after ingestion by both turaco species compared with seeds from whole fruits. Germination success of manually de-pulped seeds did not differ significantly from that of turaco ingested seeds. In contrast, seed passage through the digestive tract of rose-ringed parakeets significantly reduced germination success and viability of ingested invasive plant species. Our results suggest that Knysna and purple-crested turacos are legitimate seed dispersers of fleshy-fruited invasive plants, while rose-ringed parakeets are mainly seed predators. Although seed predation by rose-ringed parakeets negatively affects the reproductive success of these plants, it is unlikely that this will suppress the spread of these invasive alien plants in South Africa as they are already well established. Furthermore, they can facilitate dispersal by seed regurgitation and dropping uneaten fruits away from the parent plant. Similar trends could be expected for indigenous seeds that rose-ringed parakeets feed on and therefore these birds remain a negative influence within invaded ecosystems.

Light interference and melatonin affects digestion and glucocorticoid metabolites in striped mouse

Animals secrete glucocorticoids to deal with daily stressors. Studies have found that supplemental melatonin decreases glucocorticoid metabolite levels in stressed animals. We determined the effect of light interference (LI) and supplemental melatonin on (1) body mass, (2) food intake and (3) glucocorticoid metabolite levels of the striped mouse (Rhabdomys pumilio). Experiment was split into three phases: 8 L: 16 D; 8 L: 16 D with a 15 min light interruption every 4 h; and 8 L: 16 D with a 15 min light interruption every 4 h and melatonin (0.2 μg/ml) added to the water. Body mass was significantly different between phases with lowest body mass (89.17 ± 6.56 g) occurring during standard 8 L: 16 D. LI and melatonin significantly increased body mass. LI increased and melatonin decreased glucocorticoid metabolite levels. LI significantly increased and melatonin significantly decreased assimilation efficiencies possibly due to changes in energetic demands.

Digestive parameters and energy assimilation of Cape porcupine on economically important crops

To better understand how Cape porcupines are able to successfully occupy many agricultural lands, we studied their digestive parameters and energy assimilation when fed three economically important agricultural crops (potatoes [Solanum tuberosum], sweet potatoes [Ipomoea batatas] and butternut [Juglans cinerea]). Daily food intake, daily gross energy intake, daily faecal energy loss, daily energy assimilated, daily water intake and apparent assimilation efficiency were calculated for each porcupine and for each diet trial. Cape porcupines maintained body mass on all three experimental diets and energy intake ranged from 3 002.36 kJ kg-1 d-1 (potato) to 4 499.00 kJ kg-1 d-1 (sweet potato). The moisture content in each experimental diet was relatively high (>60%) and preformed water intake of winter acclimated Cape porcupines ranged from 60 ml kg-1 d-1 (potato) to 100 ml kg-1 d-1 (sweet potato). Assimilation efficiencies were high (>85%) on all three diets. Cape porcupines ingested c. 1.5–2.7 kg of each crop daily, translating to potentially large economic impacts on farmers. Knowledge and understanding of Cape porcupine food intake and dietary requirements give insight to their potential impact on commercial crops. This may aid in developing management and conservation strategies needed to manage this human—wildlife conflict.

Ground cavity nest temperatures and their relevance to Blue Swallow Hirundo atrocaerulea conservation

Blue Swallows Hirundo atrocaerulea are Critically Endangered within South Africa. They nest in natural underground holes in mist-belt grasslands. Temperature dataloggers were used to record ground cavity nest (Tn) and ambient temperature (Ta) for one artificial and 11 natural Blue Swallow nests. Mean ground cavity Tn was significantly different to mean Ta. Tn ranged from 17.0 ± 0.1 °C to 28.5 ± 0.3 °C and varied less than Ta (14.0 ± 0.2 to 47.7 ± 0.4 °C). Mean ground cavity Tn averaged 3.3 ± 0.9 °C warmer than mean Ta for 58% of nests, and mean Ta averaged 2.6 ± 0.5 °C warmer than mean ground cavity Tn for 42% of nests. There was no significant difference in mean ground cavity Tn for the aardvark-excavated holes (22.7 ± 1.6 °C) and sinkholes (21.5 ± 1.2 °C). Blue Swallows also nest in man-made holes, potentially a way to increase nesting sites. Mean aardvark-excavated Tn (19.2 ± 0.1 °C) was significantly warmer than mean artificial cavity Tn (18.5 ± 0.2 °C). Further investigation of breeding success of Blue Swallows in relation to Tn, incubation strategies and predation risk needs to be addressed in future studies for a better understanding of their reproductive ecology.

No Effects of Huddling on Core Body Temperature in Rock Hyrax, Procavia capensis

Huddling is a behavioural energy conservation mechanism that is widely used by many small endotherms at low ambient temperatures. Huddling has many benefits, including decreasing the metabolic cost of maintaining body temperature (Tb), reducing the amount of heat lost to the environment, and increasing the local temperature of the nest. To test the effects of huddling on Tb, 10 rockhyrax, Procavia capensis, were housed in outside cages in four groups, varying from one to four individuals. iButtons® were surgically implanted into each rock hyrax to record their Tb every 15 min from August to November. Despite considerable variations in ambient temperatures, the rock hyrax were found to display some degree of heterothermy by varying their mean Tb from 36.70 to 37.72°C (n = 10) but not allowing it to drop below 33.60°C or rise above 39.67°C. Contrary to what was predicted, rock hyrax did not display any significant effects of huddling on Tb, irrespective of group size.

Digestive efficiency of indigenous and invasive avian species fed fruit of invasive alien plants in South Africa

Many highly invasive plant species produce fleshy fruit that are consumed and dispersed by frugivorous birds. However, little is known about assimilation efficiency of invasive fruit by indigenous and invasive avian species. We investigated whether indigenous Knysna (Tauraco corythaix) and Purple-crested (Gallirex porphyreolophus) Turacos and invasive alien Rose-ringed Parakeets (Psittacula krameri) met their energy demands when fed fruits of four fleshy fruited invasive alien plant species: Solanum mauritianum, Cinnamomum camphora, Psidium guajava and Morus alba. Birds were fed single-fruit diets for two consecutive days and energetic parameters were calculated for all fruit diets. Our results showed that generally both invasive and indigenous avian species managed to gain their daily energy requirements from fruits of the four respective invasive plants, suggesting that they can meet their energetic demands by feeding on them only. The exception was P. krameri, which did not feed on S. mauritianum fruit. These findings may explain why fruits of invasive alien plants are attractive to most avian frugivores and highlight the role of avian frugivores in their dispersal.