This study investigated primary seed dispersal of !nara (Acanthosicyos horridus) by Blackbacked Jackals (Canis mesomelas) and secondary seed dispersal by scatter-hoarding hairyfooted gerbils (Gerbilliscus (Gerbillurus) spp.) in the central Namib Desert. This was accomplished by examining visitation rates and fruit removal of !nara melons, primarily by jackals. In addition, I determined the viability and germination rate of !nara seeds collected from jackal scat. The results indicate that jackals were the dominant species to visit !nara (93.3%) and the only !nara frugivores recorded by camera traps over two !nara fruiting seasons. There was no difference in the viability of ingested seeds and control seeds, but germination rates of ingested !nara seeds were significantly higher (50.4%) than control !nara seeds (34%). This component of the study suggests that Black-backed Jackals are the main primary dispersers of !nara seeds in the central Namib Desert. I furthermore examined secondary seed dispersal by tracking !nara seeds to determine whether scatter-hoarding hairyfooted gerbils were caching or consuming seeds. I recorded the distance moved, depth of seed burial, recovery rate and the habitats in which seeds were buried in three habitat types. Hairyfooted gerbils removed 100% !nara seeds from experimental sites and cached 60.3 % of all the !nara seeds removed. The gerbils frequently retrieved the buried caches within two days (77% of the time) and re-cached them elsewhere. The majority of caches were in the open areas (83%) and only consisted of one (39%) or two seeds (45%). Only 1.7% of the cached seeds were not retrieved by the gerbils during the 30-day observation periods. !Nara seeds were moved an average distance of 29.1±1.6 m and buried at an average depth of 4±0.2 cm. Although there is high probability of cache retrieval, some of the cached seeds survived. As gerbil caches are at favourable locations for plant establishment, and as it is more likely that buried seeds will survive until suitable conditions for germination and seedling establishment, seed dispersal by hairy-footed gerbils is advantageous to !nara plants. Therefore, hairy-footed gerbil species in the central Namib Desert contributed to secondary seed dispersal of !nara. The combined interaction of endozoochory by Black-backed Jackals (Canis mesomelas) and synzoochory by hairy-footed gerbils (Gerbillurus spp.) in dispersing seeds of !nara plants (Acanthosicyos horridus) in the central Namib Desert suggest diplochory is highly likely.

Dispersal is a critical life-history component; it determines gene flow and has profound effects on population structure, demography, social systems, and population viability. To add to our knowledge of dispersal and, in particular, our understanding of the relationship between dispersal and inbreeding, I studied three aspects of the biology of the red-cockaded woodpecker: dispersal of breeding females; the costs, benefits, and frequency of inbreeding; and the effect of inbreeding on natal dispersal. Dispersal of breeding female red-cockaded woodpeckers is strongly associated with inbreeding avoidance and mate choice, weakly associated with site choice, and not found to be associated with social constraints. Estimates of mortality for non-dispersing and dispersing breeding females were 24 and 59 percent per year, respectively-rare evidence of the cost of breeding dispersal. Significant costs of close inbreeding were found. Closely related pairs (kinship coefficient greater than 0.1) had lower hatching success as well as lower survival and recruitment of fledglings than unrelated pairs. Moderately related pairs (kinship coefficient between 0 and 0.1) and moderately inbred individuals had increased hatching success, but did not produce more young. Despite documented costs of close inbreeding and a predictable spatial distribution of closely related males near the natal territory, female fledglings disperse a median of only two territories and a modal distance of one territory. Natal dispersal of females is affected by closely related males on the natal site but unaffected by closely related males or moderately related males that are off the natal site. / Master of Science

No description available.

The success or failure of many organisms to respond to the challenges of habitat destruction and a warming climate lies in the ability of plant species to disperse between isolated habitats or to migrate to new ranges. European semi-natural grasslands represent one of the world's most species-rich habitats at small scales, but agricultural intensification during the 20th century has meant that many plant species are left only on small fragments of former habitat. It is important that these plants can disperse, both for the maintenance of existing populations, and for the colonisation of target species to restored grasslands. This thesis investigates the ecological, geographical and historical influences on seed dispersal and connectivity in semi-natural grasslands, and the mobility of plants through time and space. Seed dispersal by human activity has played a large role in the build-up of plant communities in rural landscapes, but patterns have shifted. Livestock are the most traditional, and probably the most capable seed dispersal vector in the landscape, but other dispersal methods may also be effective. Motor vehicles disperse seeds with similar traits to those dispersed by livestock, while 39% of valuable grasslands in southern Sweden are connected by the road network. Humans are found to disperse around one-third of available grassland species, including several protected and red-listed species, indicating that humans may have been valuable seed dispersers in the past when rural populations were larger. Past activities can also affect seed mobility in time through the seed bank, as seeds of grassland plant species are shown to remain in the soil even after the grassland had been abandoned. Today however, low seed rain in intensively grazed semi-natural grasslands indicates that seed production may be a limiting factor in allowing seeds to be dispersed in space through the landscape. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Accepted. Paper 4: In press. Paper 5: Manuscript.</p>

The dispersal of plants with particular attention to the roles birds play as dispersal agents was studied in the southwestern Cape, South Africa from 1983 to 1985. The research was organized as ten inter-related studies, each with an independent data base. Each chapter focused on a different scale of plant dispersal processes ranging from regional assemblages of plant species to individual species. At the largest scale, the seven vegetation types commonly occurring in the southwestern Cape were examined for incidence of vertebrate-dispersed plants. Coastal Thicket and Afromontane Forest were found to be the richest in these species. The colonization of vertebrate-dispersed plants was examined in an artificially cleared area of Mountain Fynbos vegetation. Enhanced densities of vertebrate-dispersed species were found in areas where perches had been provided. The seasonal availability of vertebrate-dispersed species was found to be most continuous in Coastal Thicket vegetation. Fruit displays of vertebrate-dispersed indigenous plants were found to vary from those that were sporadic and inconspicuous, to those that were conspicuous and predictable, whereas those of alien plants were usually large and conspicuous. Avian use of these fleshy fruits in Coastal Thicket was examined and found to be proportional to their availability. A study of fruit presentation in relation to leaf number and stem thickness suggested that sessile, stem attached fruits have fewer local leaves at time of ripening than fruits which are presented in panicles. This may enhance accessibility and conspicuousness of stem attached fruits for dispersal by birds. Four autecological studies tested certain predictions arising from models developed to describe fruit/frugivore interactions. The dispersal of the alien Acacia cyclops seeds by the indigenous Black Korhaan Eupodotis afra suggested that successful fruit/frugivore relationships are not necessarily the product of reciprocal evolution. The study on Chrysanthemoides monilifera found that efficient dispersal systems are not limited to plants producing small quantities of lipid-rich fruits and to dispersal by obligate frugivores. The abiotic dispersal of Quercus robur was found to be efficient in relation to vertebrate-dispersal. The study on Protasparagus aethiopicus found that the morphology of fleshy fruits may also reflect attempts to overcome the effects of non-dispersing seed predators. 1It is concluded that a gradient from a predictable to unpredictable fruit availability provides a better basis for studying fruit/frugivore interactions than the coevolutionary models. previously presented.

Dispersal influences several ecological and evolutionary processes, such as intraspecific competition, genetic drift and inbreeding. It can lead to phenotypic mismatch with the habitat when a locally adapted individual winds up in an environment with a divergent selection regime compared to the source habitat. The aim of this project was to compare dispersive traits in the freshwater isopod Asellus aquaticus from a cave habitat, with surface dwelling isopods collected upstream and downstream from the cave system. The subterranean stream (cave) represents a rare, geographically limited habitat which has a divergent selective pressure compared to the surrounding habitats. Experiments on dispersal were performed in the laboratory, in darkness with IR-equipment for visualization. Displacement was measured using one-dimensional test arenas. Compared to the surface phenotype, the cave phenotype was expected to have reduced fitness outside of the cave and unlikely to successfully disperse to new areas of similar suitable conditions. The results did not follow my main hypothesis that isopods from the cave would be less dispersive than individuals from the surface. The inconclusive results might derive from large variation in the data and divergent adaptations which yield similar expression of dispersal.

published_or_final_version / abstract / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

published_or_final_version / Biological Sciences / Master / Master of Philosophy

H.rotundifrons A. Milne Edwards, 1867, the big-handed crab, belongs to the Belliidae and is the only crab representative of this family in New Zealand. It lives in the intertidal zone. The megalopae undergo 13-16 moults to become fully mature at a size of 11-13mm CWo These mature crabs live up to a maximum of 19 years and attain a size of 23-25mm CW (24-26 instars). The laboratory growth curve of H.rotundifrons is asymptotic and there is no terminal ecdysis. Growth is similar between the sexes up to maturity but decreases more in males after puberty thus exhibiting an "anomalous" pattern. Average weight gain after ecdysis was found to be same for both sexes and independent of size (approx. 18%). Environmental and physical factors which normally affect growth have no profound effect on H.rotundifrons. However, moult frequency was found to be increased by removal of eyestalks or when crabs were maintained in constant darkness. Starvation and limb removal considerably reduced the moult increment. Alpha ecdysone concentration increased to a peak 40 days before ecdys is and returned to base 1eve1s at moulting. Moulting is seasonal having a high peak in mid-summer and a smaller peak in April-May. A field study of dispersal showed that short-range movements (5.06m), within the intertidal zone, are common for H.rotundifrons (n=212). Many crabs left their refuge between low tides and their movements were independent of one another. Neither home range nor long dispersal movement (>21m) have been observed in H.rotundifrons. Diet of H.rotundifrons comprised algae (60.7%), crustaceans (19.6%), sand & unidentified materials (11.7%), sponges & worms (5.7%), and molluscs (2.3%). Although brown algae were always the single dominant food item, diet composition varied seasonally. The majority of the population at Kaikoura (602(M):858(F)) consisted of pre-pubertal males and females and fewer post-pubertal males were found than post-pubertal females, a reflection of slower male growth and suggesting higher male mortality.

Recent observed changes in bird distributions provide an unprecedented opportunity to gain a deeper understanding of the processes that influence species' persistence. By modelling presence-absence data from the North American Breeding Bird Survey, we found evidence that the breeding range of the western burrowing owl has contracted at its northern, western, and eastern boundaries since 1967. We suggest that the species' breeding distribution is also expanding southwards to former wintering grounds into northern Mexico, facilitated by the appearance of new breeding habitat created by irrigated agriculture in the arid areas of southwestern United States and northwestern Mexico. This dissertation explores the hypothesis that burrowing owls from northern migratory populations have become resident breeders in areas of northwestern Mexico that were formerly used only by migratory owls during winter, contributing to both population declines near the northern extent of the species' breeding range and population increases in the southern half of the species' range. We used novel DNA microsatellite markers to test patterns of gene flow predicted by this migration-mediated range-shift hypothesis. We genotyped 1,560 owls from 36 study locations in Canada, Mexico, and the United States. Analyses of molecular variance provided evidence that burrowing owl populations in both northwestern Mexico and Canada are genetically different from the rest of the populations in the breeding range, lending some support to the migration-mediated range-shift hypothesis. We found evidence of subtle genetic differentiation associated with subtropical irrigated agricultural areas in southern Sonora and Sinaloa, demonstrating that land use can produce location-specific population dynamics leading to genetic structure even in the absence of dispersal barriers. We also used stable isotopes 2/H, 13/C, and 15/N in feathers to test philopatry and breeding dispersal patterns predicted by this migration-mediated range-shift hypothesis. Burrowing owl populations near the northern edge of the species' breeding range had a high proportion of immigrants compared to interior populations, while other populations had high levels of philopatry. Stable isotopes also provided evidence of breeding dispersal events from Canadian populations to northwestern Mexico in support of the migration-mediated range-shift hypothesis, but similar isotope signatures in nestling feathers between these two regions prevent stronger inferences.