Browsing by Subject "Ecology"
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- ItemOpen AccessA study of bush encroachment in Hluhluwe National Park, using aerial photographs within a GIS framework(2003) Aston, TimBush encroachment has been an ongoing process since the proclamation of the Hluhluwe Reserve. In this paper, I assess both the total extent of bush encroachment over the last 40 years for a section of the reserve (9.1 %}, as well as which landscape factors pre-dispose areas to encroachment in that section. Aerial photographs from 1960 were linked together and aligned to an orthorectified Image from 2000, which had been georeferenced and aligned to the GIS database that exists for the area. Areas of closed canopy vegetation were converted into polygons, and the physical attributes of the areas that had been encroached Upon were extracted from the GIS database that exists for the area. Classification trees were used for the analysis of landscape correlates of encroachment. Fire frequency and the area of forest within 200m of a point in? 1960 were Identified as being the main factors determining which areas had been encroached upon
- ItemOpen AccessBiophysical interactions in the Iceland Basin(2008) Harington, Amy; Lucas, Michael IThe Iceland Basin in the N. Atlantic has attracted considerable recent attention because the spring bloom in this region acts as the most powerful biological carbon pump anywhere in the world oceans. Furthermore, the link between primary productivity and herbivory by the calanoid copepod, Calanus finmarchicus provides the trophic link between primary producers and the important commercial fishery for Atlantic Cod. However, one result of ocean warming is that the distribution of the cold water loving Calanus finmarchicus is being pushed northwards which adversely affects the food supply to juvenile Cod. Perhaps of more serious concern are concerns that the biological carbon pump may weaken as a result of increased thermal stratification and therefore reduce upward nitrate flux to drive nitrate-based export production. This was in fact confirmed at least in the study region which is dominated by regenerated production (f-ratio <0.5) which in turn suggests a shift in community structure from larger celled organisms to smaller celled organisms, characterised by long inefficient food chains. This project makes use of summer cruise data to the Iceland Basin last summer (2007) where measurements of 15N derived new production (NP) were made to add to previous seasonal (spring, winter) measurements of NP in the region.
- ItemOpen AccessBorderlands and Political Ecology: A photographic exploration of the environment, territories, boundaries and power near the imaginary line of the equator(2020) Meyer, Garth; Josephy, SveaFor several years I have photographed primary hardwood forests along the imaginary line of the equator to communicate, persuade and warn of the continued ecological destruction that is occurring along this line. My plan was to capture arcadian visions of equatorial hardwood primary forests before they are destroyed and to show how this arcadian vision is disrupted by a more dystopian one. The images in this project were photographed in three areas that circle the equator: Southeast Asia, Africa and South America, where over half the world's rainforests are concentrated, and which I visited to follow the line. Line is an attempt to understand the current pressures on the equatorial environment and create a photographic exploration of ecology that highlights and foregrounds land, space, territories, boundaries and power. For this, myfield of study and research considers ecology through the theory and lens of photography.
- ItemOpen AccessThe burning questions about Hluhluwe : causes and consequences of a severe wildfire(2009) Browne, Catherine; Bond, William J; Midgley, Jeremy JThe biophysical drivers of fire; ignition, fire weather conditions, fuel biomass, and flammability, differ in varying ecosystems. The rates of occurrence of these factors influence fire regimes. This study investigated the causes and consequences of a severe wildfire that swept through the Hluhluwe Game Reserve, KwaZulu-Natal South Africa in September 2008. This fire was an extreme event that seems only to have been possible due to the combination of circumstances that occurred in the days prior to and during the 14th/15th September 2008. The event was considered extreme because it burnt from savanna into thicket and forest patches, which is atypical of fires. The fire caused large structural change in tree demography, however, not much change in densities. The results of this study indicate that coupled weather conditions conducive to fire; namely low relative humidity, high temperatures and high wind speeds, occurred at the time of the fire. The synergistic influences of fire weather conditions and the state of available fuel caused this severe fire. The fire continued to bum for 48 hours before weather conditions relaxed and became less dangerous. These data suggest extreme fires such as the September 2008 event may be exploited by managers to reclaim former grasslands and savannas that have suffered the effects of bush encroachment and/or create open areas allowing grasslands to develop. However, severe fires run the risk of leading to the loss of forests and the biodiversity that they support. This study has identified the conditions likely to promote such severe fires.
- ItemOpen AccessCollapse of an iconic conifer: long-term changes in the demography of Widdringtonia cedarbergensis using repeat photography(2016) White, J D M; Jack, S L; Hoffman, M T; Puttick, J; Bonora, D; Visser, V; February, E CBACKGROUND: Conifer populations appear disproportionately threatened by global change. Most examples are, however, drawn from the northern hemisphere and long-term rates of population decline are not well documented as historical data are often lacking. We use a large and long-term (1931-2013) repeat photography dataset together with environmental data and fire records to account for the decline of the critically endangered Widdringtonia cedarbergensis. Eighty-seven historical and repeat photo-pairs were analysed to establish 20th century changes in W. cedarbergensis demography. A generalized linear mixed-effects model was fitted to determine the relative importance of environmental factors and fire-return interval on mortality for the species. RESULTS: From an initial total of 1313 live trees in historical photographs, 74% had died and only 44 (3.4%) had recruited in the repeat photographs, leaving 387 live individuals. Juveniles (mature adults) had decreased (increased) from 27% (73%) to 8% (92%) over the intervening period. Our model demonstrates that mortality is related to greater fire frequency, higher temperatures, lower elevations, less rocky habitats and aspect (i.e. east-facing slopes had the least mortality). CONCLUSIONS: Our results show that W. cedarbergensis populations have declined significantly over the recorded period, with a pronounced decline in the last 30 years. Individuals that established in open habitats at lower, hotter elevations and experienced a greater fire frequency appear to be more vulnerable to mortality than individuals growing within protected, rocky environments at higher, cooler locations with less frequent fires. Climate models predict increasing temperatures for our study area (and likely increases in wildfires). If these predictions are realised, further declines in the species can be expected. Urgent management interventions, including seedling out-planting in fire-protected high elevation sites, reducing fire frequency in higher elevation populations, and assisted migration, should be considered.
- ItemOpen AccessThe dispersal paradox : can lowland granivorous mice also disperse the seeds they devour?(2003) Gwynne-Evans, David; Midgley, Jeremy JThe relationship between two rodent species and the Cape Reed (Willdenowia incurvata) were examined. Many studies have focussed on the role of rodents as predators of plant seeds. However, it seems that certain rodents may actually perform a crucial role in the dispersal of plants. Experiments to uncover the dispersal mechanism were carried out. Also examined is the role of the appendages present on the Restio seeds, possibly as energy-rich rewards for dispersal for the rodents. It was found that the Restio may be dependent on seed-dispersing rodents, although this mutualism is not so important in fragmented habitats.
- ItemOpen AccessDrivers and uncertainties of future global marine primary production in marine ecosystem models(2015) Laufkötter, C; Vogt, M; Gruber, N; Aita-Noguchi, M; Aumont, O; Bopp, L; Buitenhuis, E; Doney, S C; Dunne, J; Hashioka, T; Hauck, J; Hirata, T; John, J; Le Quéré, C; Lima, D I; Nakano, H; Seferian, R; Totterdell, I; Vichi, M; Völker, CPast model studies have projected a global decrease in marine net primary production (NPP) over the 21st century, but these studies focused on the multi-model mean and mostly ignored the large inter-model differences. Here, we analyze model simulated changes of NPP for the 21st century under IPCC's high emission scenario RCP8.5 using a suite of nine coupled carbon–climate Earth System Models with embedded marine ecosystem models with a focus on the spread between the different models and the underlying reasons. Globally, five out of the nine models show a decrease in NPP over the course of the 21st century, while three show no significant trend and one even simulates an increase. The largest model spread occurs in the low latitudes (between 30° S and 30° N), with individual models simulating relative changes between −25 and +40%. In this region, the inter-quartile range of the differences between the 2012–2031 average and the 2081–2100 average is up to 3 mol C m-2 yr-1. These large differences in future change mirror large differences in present day NPP. Of the seven models diagnosing a net decrease in NPP in the low latitudes, only three simulate this to be a consequence of the classical interpretation, i.e., a stronger nutrient limitation due to increased stratification and reduced upwelling. In the other four, warming-induced increases in phytoplankton growth outbalance the stronger nutrient limitation. However, temperature-driven increases in grazing and other loss processes cause a net decrease in phytoplankton biomass and reduces NPP despite higher growth rates. One model projects a strong increase in NPP in the low latitudes, caused by an intensification of the microbial loop, while the remaining model simulates changes of less than 0.5%. While there is more consistency in the modeled increase in NPP in the Southern Ocean, the regional inter-model range is also very substantial. In most models, this increase in NPP is driven by temperature, but is also modulated by changes in light, macronutrients and iron as well as grazing. Overall, current projections of future changes in global marine NPP are subject to large uncertainties and necessitate a dedicated and sustained effort to improve the models and the concepts and data that guide their development.
- ItemOpen AccessDung beetles eat plants : insights into the nutritional world of Euoniticellus intermedius (Reiche) (Coleoptera: Scarabaeinae)(2007) Yates, Megan; Midgley, Jeremy J; Byrne, MarcusDung beetle eggs develop within the finite nutritional environment of the brood ball, which is made using maternally processed animal faeces. It is thought that microbial and gut-derived excretions constitute the major source of N and C for adult dung beetles, while developing larvae, which have retained the mouthparts of their saprophagous ancestors, digest larger particles in the brood ball and rely on symbionts present in the brood ball to provide breakdown products for their nutrition. Stable isotope analysis was used to trace the source of developing larval N and C. Nitrogen and carbon contents, as well as C: N ratios, were used to assess the nutritional quality of this finite food source and to track the changes in these values during the course of development. The main source of both larval and adult N and C was plant-derived and preferential assimilation of gut-derived excretions present in the dung did not occur. Symbionts, including fungi, did not appear to play a significant role in larval nutrition. Extensive amino acid recycling occurs during metamorphosis, indicated by the 0.53 %0 enrichment in 815N in emergent beetles. Maternal processing of bulk dung creates an enhanced nutritional environment for offspring and the maternal faecal deposit, on which the egg is positioned, provides the larvae with an initial, nutrient-rich source of food.
- ItemOpen AccessThe ecology of invasions by Pinus (pinaceae) and Hakea (proteaceae) species, with special emphasis on patterns, processes and consequences of invasion in mountain fynbos of the southwestern Cape Province, South Africa(1989) Richardson, David Mark; Cowling, Richard MThe fire-prone mountain fynbos of the southwestern Cape Province of South Africa has been severely invaded by introduced trees and shrubs. These invasions have transformed fynbos shrublands to dense thickets of trees and shrubs in many parts of the region, thus disrupting various natural ecosystem processes. The ecology of invasions by species of Pinus and Hakea (the most successful genera) was studied using a series of natural experiments in conjunction with autecological studies. The study was divided into main four parts: (i) case studies to elucidate major patterns and processes of invasion; (ii) studies of the life history and population ecology of selected invaders; (iii) studies of the determinants of invasibility; and (iv) assessments of the consequences of invasion and of control programmes. Bibliography: pages 235-272.
- ItemOpen AccessThe effect of light-limitation on spinescent structural defence and its implications on resistance to herbivory in the shade(2013) Adams, Ismat; Bond, William J; Dominique, Tristan-CharlesPlants can resist herbivore pressure through structural or chemical defence or both. The ultimate goal of defence against herbivory is to reduce the amount of damage to biomass, but more specifically to protect against damage to meristematic tissue. The defences employed depend on the type of herbivory experienced, which is contingent on the herbivore and its mouthparts. This investigation was concerned with structural defence presented by spines. This type of defence protects against mammalian herbivores such as browsers. Spiny species do not dominate in low-light deep forest environments. Therefore the aim of this study was to determine the constraints on spines as a defence strategy under shaded conditions by assessing the effect of reduced light on spine efficiency. Spine efficiency was defined as the amount of defence afforded the plant given the resources available. Spines require carbon to be built and need to be arranged properly in order to present an adequate defence. Thus two non-mutually exclusive hypotheses were proposed: Light limitation reduces the ability of spines to present an adequate defence against browsers due to the architectural strategy employed and/or its influence on carbon gain. The spinescent plant chosen for study was Carissa macrocarpa (Ecklon) A.DC. Light condition of plants was determined using hemispherical photography. Spine efficiency of sun and shade plants was determined using a bite test and was evaluated using architectural and physiological analyses. Architectural analysis involved identifying levels of organisation within the plant across ontogeny and indentifying sun and shade growth strategies. Physiological analysis involved determining carbon gain of sun and shade individuals using gas-exchange measurements, as well as the measurement of biomass allocation by harvesting and oven drying different plant parts. Results showed that biomass allocation patterns of C.macrocarpa did not change in sun and shade but total biomass increased from shade to sunlit conditions. Architectural analysis revealed that in the sun the plant adopted a stout dense structure with high spine efficiency, while in the shade it was more elongated with lower spine efficiency. Therefore C.macrocarpa adapts to the light environment by adopting either the shade or the sun architectural strategy. The way in which this works is that light affects carbon gain, which either increases or decreases biomass and in turn leads the plant to adopt the sun or shade architectural strategy. The architectural strategy affects spine efficiency such that plants in the sun have higher spine efficiency than plants in the shade. Thus, spinescent plants do not do well in light limited environments because they are architecturally constrained to elongate in such conditions. This constraint would put them at higher risk of browser damage than plants in light-sufficient conditions, ultimately decreasing their fitness. If the patterns observed in C. macrocarpa prove to be general, then it helps to explain why spiny plants are more commonly found in open, sunlit environments than in deep shade.
- ItemOpen AccessFrog eat frog: exploring variables influencing anurophagy(2015) Measey, G John; Vimercati, Giovanni; de Villiers, F André; Mokhatla, Mohlamatsane M; Davies, Sarah J; Edwards, Shelley; Altwegg, ResBackground. Frogs are generalist predators of a wide range of typically small prey items. But descriptions of dietary items regularly include other anurans, such that frogs are considered to be among the most important of anuran predators. However, the only existing hypothesis for the inclusion of anurans in the diet of post-metamorphic frogs postulates that it happens more often in bigger frogs. Moreover, this hypothesis has yet to be tested.
- ItemOpen AccessHI in group interactions: HCG 44(2017) Hess, Kelley M; Cluver, M E; Yahya, Sahba; Leisman, Lukas; Serra, Paolo; Lucero, Danielle M; Passmoor, Sean S; Carignan, ClaudeExtending deep observations of the neutral atomic hydrogen (H I) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example, and we have combined H I data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (N _{H {I}}
- ItemOpen AccessHunting as a management tool? Cougar-human conflict is positively related to trophy hunting(2016) Teichman, Kristine J; Cristescu, Bogdan; Darimont, Chris TBACKGROUND: Overexploitation and persecution of large carnivores resulting from conflict with humans comprise major causes of declines worldwide. Although little is known about the interplay between these mortality types, hunting of predators remains a common management strategy aimed at reducing predator-human conflict. Emerging theory and data, however, caution that such policy can alter the age structure of populations, triggering increased conflict in which conflict-prone juveniles are involved. RESULTS: Using a 30-year dataset on human-caused cougar (Puma concolor) kills in British Columbia (BC), Canada, we examined relationships between hunter-caused and conflict-associated mortality. Individuals that were killed via conflict with humans were younger than hunted cougars. Accounting for human density and habitat productivity, human hunting pressure during or before the year of conflict comprised the most important variables. Both were associated with increased male cougar-human conflict. Moreover, in each of five regions assessed, conflict was higher with increased human hunting pressure for at least one cougar sex. CONCLUSION: Although only providing correlative evidence, such patterns over large geographic and temporal scales suggest that alternative approaches to conflict mitigation might yield more effective outcomes for humans as well as cougar populations and the individuals within populations.
- ItemOpen AccessThe Influence of dust deposition, carbonates and erosion on the formation of Clanwilliam heuweltjies(2013) Adams, Ismat; Khomo, LesegoHeuweltjies (Afrikaans for "little hills") are non-anthropogenic, regularly dispersed earth mounds up to 32 meters in diameter and approximately 1.4 meters in height, that dot about 25% of the land surface of south-western southern Africa. The zoogenic "termite" hypothesis has been widely accepted as a hypothesis of heuweltjie origin. However, the recent "vegetation-patch-erosion" (VPE) hypothesis suggests an equally likely explanation for heuweltjie formation. The aim of this investigation was firstly to determine the influence of dust deposition and carbonates on heuweltjie formation in order to gain insight into the formative process of heuweltjies. The second part of this investigation sought to further test the VPE hypothesis by examining whether erosion alone could give rise to heuweltjies within a reasonable time frame. Soil surveys were conducted on 8 heuweltjies and at 2 inter-heuweltjie areas at depths of up to 0.9m. Textural analysis of soil samples collected from the 8 heuweltjies as well as an additional 11 heuweltjies was conducted. Bulk density was also evaluated for each horizon of each heuweltjie and inter-heuweltjie. Carbonates in all soil samples were determined by acid digestion of soils. A digital elevation model of the Clanwilliam area was constructed and used to obtain heuweltjie area and elevation. There was no difference in average soil texture moving from the centre of a heuweltjie to its periphery (indicating that they formed by layered stratification rather than radially from the centre). There was an apparent difference in texture and carbonates between heuweltjie and inter-heuweltjie zones. Mass of fines (silt and clay) and carbonates were both positively correlated with heuweltjie mass, but were also collinear. Non-parametric regression of heuweltjie mass against both fines and carbonates revealed a clear linear trend. However, the trend between fines and carbonates suggested that fines played a central role in both heuweltjie and carbonate formation and that carbonate took on only a secondary role in heuweltjie formation. Erosion alone would have taken 11000 years to form the heuweltjies. However, some calcretes within heuweltjies have been found to be older than 11000 years, suggesting that erosion has not had a major influence on heuweltjie formation. These findings support the vegetation-patch-erosion hypothesis. However they support dust deposition rather than erosion as a primary contributor to heuweltjie formation.
- ItemOpen AccessInsurers could help address climate risks(Nature Publishing Group, 2011) Nel, Deon; Shearing, Clifford; Reyers, BelindaWorking with South Africa's largest short-term insurer, Santam, we investigated how communities should manage the increased risks associated with climate change. The global insurance industry has focused on refining the quantification, differentiation and pricing of the risk exposure of insured assets. Our findings call into question a sole reliance on this strategy (J. Nel et al. CSIR/NRE/ECOS/2011/0063/B; CSIR, 2011).
- ItemOpen AccessInvestigating the impacts of donkeys on a communal range in Namaqualand: how much does a donkey "cost" in goat units?(1996) Vetter, Susanne; Bond, William J; Hoffmann, TimmDonkeys are used extensively in Namaqualand and other rural areas in South Africa for pulling carts, carrying loads, ploughing and threshing grain. There is, however, an ongoing debate among farmers, agriculturalists and the wider population about the implications of keeping donkeys, particularly on communal lands. Donkeys are reported to cause more damage to the veld than other animals, and it is commonly said that one donkey eats as much as seven goats. This project was initiated as a case study to investigate the impacts of donkeys in a communal area in the succulent shrublands of Namaqualand, and to generate suggestions for the management of donkey populations. The degree of competition between goats and donkeys was investigated by predicting daily food intake using a model based on ruminant and non-ruminant digestion, which takes into account the animal's body weight and digestibility characteristics of its diet. The ratio predicted food intakes is discussed in the light of the degree of dietary and habitat overlap, which were obtained from field observations. Habitat use was scored using dung frequency transects, and feeding was directly observed. It was found that in the wet season, one donkey eats as much as 5 / 7.6 goats (donkey weight set at 200 and 250 kg respectively). In the dry summer, this ratio increases to 7.6 / 8.6 because in ruminants, the passage of food through the gut slows down as the digestibility of the diet decreases. Habitat overlap is concentrated in the riverine areas and sandy pediments, which make up 15 % of the landscape and are strongly favoured by donkeys. No significant differences were found to exist between the intensities of goat use of the different habitats. The botanical composition of the diets of donkeys and goats were found to be similar, but there is a great difference in the quality of the diet consumed by each species as goats are able to select plant parts of a higher quality. The implications of this are that whereas a donkey takes in as much dry matter as 5 - 8.6 goats, the diet of this food is not high enough to satisfy the dietary requirements of goats, and hence fewer goats than predicted can be supported for every donkey that is eliminated. Donkeys are commonly reported to have destructive feeding habits; little of this was directly observed, but donkeys were found to bite deeper into the wood of shrubs, which may damage the plants in the long term. There are two main management measures that should be applied. The feral donkey population in Paulshoek, estimated at 50-100 animals, must be eliminated - even at a conservative estimate, these animals could be replaced with 250 goats. However, one must look beyond the number to the processes taking place to make management effective. Even if one donkey can be replaced with fewer than 5 goats, the vegetation is relieved of the indirect effects donkeys have through their feeding habits. Control of working donkeys should focus on the riverine and flat, sandy areas, as they are potentially of high nutritional importance (especially the riverine areas which support grass throughout the year), and which are also the most susceptible to erosion due to their sparse vegetation cover. These areas are small and valuable, and plans should be made to protect some areas through the growing season.
- ItemOpen AccessA model of a rangeland grazing system within a management procedure approach framework(2007) Soares, Muri; Plagányi, Éva; Hoffmann, Timm; Richardson, David MarkA model describing livestock grazing system dynamics was developed and fitted to available data. This study preliminarily explored the use of a formal management procedure (MP) approach to determine appropriate annual offtake in a terrestrial system. This approach has been applied in marine systems with great success, but has never been tried in terrestrial ecosystems. Rangelands and marine systems have in common the fact that there is often an offtake component to them and so stakeholders in those systems need knowledge of optimal harvesting strategies within defined management strategies. Three models were developed that described the growth of female goats in Paulshoek. The first (basic livestock model) depicted the growth of livestock as a logistic equation with an adult survival term and an annual growth term. The second model (rainfall-livestock model) added a rainfall component, with livestock productivity modelled as a function of rainfall. The final version of the model (vegetation-rainfall-livestock model) added a vegetation component that interacted with rainfall and livestock. The rainfall-livestock model provided a statistically significant better fit to the data, followed by the vegetation-rainfall model. The vegetation-rainfall-livestock model provided a reasonable representation of livestock population changes through time, with the largest deviations evident over the period 1975-1980. Results show that environmental factors alone are unable to fully explain observed system dynamics because anthropogenic factors for which no data are available may also play a role. Preliminary exploration with a simple MP suggested that a low offtake rate of 10% provided the highest average annual offtake. Our study has shown that a rangeland stocking system can be reasonably described by a simple model that uses only rainfall data and a rainfall-vegetation-livestock interaction. Rangeland livestock systems would benefit greatly from adopting an MP approach as it would allow stakeholders to make informed decisions on stocking rates and annual offtake.
- ItemOpen AccessA nitrogen budget for the Cape Metropolitan area : is nitrogen enrichment occurring in the soils of remnant patches of lowland fynbos?(2000) Kathawaroo, Deshika; Bond, William J; Stock, William DAnthropogenic activities create nitrogenous pollutants which threaten the existence of lowland fynbos, comprising 92 Red Data Book species and 14 Cape Flats endemics. A regional Nitrogen budget was constructed through the collation of existing data for the Cape Metropolitan Area. An NOx inventory has revealed that vehicles emit 66 % of the total NOx emissions into the atmosphere. The maximum potential N deposition is 184 kg N ha⁻¹ yr⁻¹ for the lowlands. Air quality in an industrial area, Goodwood, has revealed that a large proportion of the emissions remain in the air and have the potential to deposit 33 kg N ha⁻¹ yr⁻¹. Atmospheric N deposited on unimpacted coastal fynbos is 1.99 kg ha⁻¹ yr⁻¹. Thus remnant patches of lowland fynbos are threatened by replacement by grasslands as a result of atmospheric N inputs. Direct measurements of soil N pools are required, since signals of leaching in rivers may be premature as N accumulating in soil pools may not yet have reached saturation point. NH₃ emissions, wet and dry N deposition, and atmospheric transport models are required in order to construct a N budget for the CMA. Thereafter, appropriate preventative strategies can be devised in order to prevent the replacement of remnant patches of lowland fynbos.
- ItemOpen AccessSeasonal rainfall at long-term migratory staging sites is associated with altered carry-over effects in a Palearctic-African migratory bird(2016) Sorensen, Marjorie C; Fairhurst, Graham D; Jenni-Eiermann, Susanne; Newton, Jason; Yohannes, Elizabeth; Spottiswoode, Claire NAbstract Background An understanding of year-round habitat use is essential for determining how carry-over effects shape population dynamics in long-distance migratory songbirds. The recent discovery of long-term migratory staging sites in many species, prior to arrival at final wintering sites, adds complexity to efforts to decipher non-breeding habitat use and connections between sites. We investigated whether habitat conditions during migratory staging carry over to influence great reed warbler (Acrocephalus arundinaceus) body condition at final wintering sites in Zambia. We asked whether the presence/absence and strength of such carry-over effects were modified by contrasting rainfall conditions during 2 years. Results First, we found that individuals staging in a dry year had higher corticosterone (CORT f ) and stable nitrogen isotope values (suggesting higher aridity) than birds staging in a wet year, indicating that regional weather affected staging conditions. Second, we found that carry-over effects from staging habitat conditions (measured via carbon and nitrogen isotopes) to final winter site body condition (measured via scaled mass index and β-hydroxybutyrate) were only present in a dry year, suggesting that environmental factors have consequences for the strength of carry-over effects. Our results also suggest that wet conditions at final winter sites may buffer the effects of poor staging conditions, at least in the short term, since individuals that staged in a dry year had higher scaled mass indices in Zambia than individuals that staged in a wet year. Conclusions This study provides a first insight into the connections between long-term migratory staging sites and final wintering sites, and suggests that local environmental factors can modify the strength of carry-over effects for long-distance migratory birds.
- ItemOpen AccessSneaky African fig wasps that oviposit through holes drilled by other species(2009) Compton, Stephen G; Van Noort, Simon; McLeish, Michael; Deeble, Mark; Stone, VictoriaWatshamiella Wiebes species (Hymenoptera: Chalcidoidea: Pteromalidae: Sycoryctinae) were observed to engage, monitor and subsequently use oviposition holes made by other parasitoid fig wasp genera (Apocrypta Coquerel and Sycoryctes Mayr) to oviposit into host figs (Moraceae, Ficus) through the fig wall. They may be inquilines, klepto-parasitoids, or hyper-parasitoids; however, further biological investigations of larval diet are required to establish their life history strategy. Watshamiella species are morphologically robust, with enlarged fore femora and tibia, and aggressively interact with other fig wasps and ants. Our observations contribute towards unravelling the complex suite of behavioural adaptations and interactions involved in the community ecology of the obligate mutualism that exists between fig wasps and their host figs.