Graham I. H. Kerley

What do mice select for in seeds

SummaryKnowledge of the basis upon which granivores select seeds is crucial to the understanding of granivory. In this study the preferences of three rodent granivores among seeds of 11 plants from the semi-arid Karoo of South Africa were estimated, and related to the physical and chemical attributes of the seeds. Seed weights and calorific, moisture, protein, polyphenol, ash, lipid and silica contents were estimated and cell contents, soluble ash and soluble carbohydrate contents were derived from these values. These attributes were determined for both the intact seeds and the portion of the seed that is ingested by the mice. The efficiency with which mice ingested the seeds (in terms of time and mass) was recorded. All three mouse species ranked the seeds similarly, and the two species for which handling efficiency was measured did not differ in this regard. Preference hierachies were highly correlated with the rate of energy intake, as predicted by optimal foraging theory. There was no correlation between rodent preferences and the gross energy content of the seeds, emphasising the importance of measuring relevant parameters. The energy yield of the seeds calculated here, in conjunction with rodent population energy requirements and dietary data, may be used to estimate potential granivore impact on the seed production of the plant community.

Options for the conservation of large and medium-sized mammals in the Cape Floristic Region hotspot, South Africa

We assessed options for conserving the large- and medium-sized mammals indigenous to the Cape Floristic Region, South Africa, using systematic conservation planning, the first such attempt for an entire ecoregion. The potential distributions and abundances of the 41 extant species for the entire region prior to anthropogenic transformation of habitats were estimated. This was particularly useful as it obviated any reliance on records of occurrence for conservation planning. Areas that had not been transformed through agriculture or other developments were considered available for conservation. The fragments of untransformed habitat were identified as being large enough to support communities at least 25 individuals of the smallest herbivore species. Smaller fragments were not considered suitable for mammal conservation. Transformation and fragmentation had significant impacts on potential populations, and this was asymmetrical across species, being higher for lowland than montane species. The existing reserve system was estimated to effectively conserve only half the mammal species, using the criteria applied here. Two conservation goals were compared; first, either conserving only CFR endemics and threatened species; and second, conserving all the mammals (with some exceptions for marginally occurring species). Options for protected area systems were assessed using C-Plan, a decision support system designed for systematic conservation planning. The irreplaceability of the planning units varied only slightly under the two goals, and the more inclusive goal was used to develop a proposed reserve network in which targets for all the species were achieved. The CFR endemics and threatened species effectively function as umbrella species for the remaining mammals. This study demonstrates that the incorporation into systematic conservation plans of conservation targets adequate for the persistence of populations comprising communities across entire ecoregions is feasible

Desertification of subtropical thicket in the Eastern Cape, South Africa : are there alternatives ?

The Eastern Cape Subtropical Thicket (ECST) froms the transition between forest, semiarid karroid shrublands, and grassland in the Eastern Cape, South Africa. Undegraded ECST forms an impenetrable, spiny thicket up to 3 m high consisting of a wealth of growth forms, including evergreen plants, succulent and deciduous shrubs, lianas, grasses, and geophytes. The thicket dynamics are not well understood, but elephants may have been important browsers and patch disturbance agents. These semiarid thickets have been subjected to intensive grazing by domestic ungulates, which have largely replaced indigenous herbivores over the last 2 centuries. Overgrazing has extensively degraded vegetation, resulting in the loss of phytomass and plant species and the replacement of perennials by annuals. Coupled with these changes are alterations of soil structure and secondary productivity. This rangeland degradation has largely been attributed to pastoralism with domestic herbivores. The impact of indigenous herbivores differs in scale, intensity, and nature from that of domestic ungulates. Further degradation of the ECST may be limited by alternative management strategies, including the use of wildlife for meat production and ecotourism. Producing meat from wildlife earns less income than from domestic herbivores but is ecologically sustainable. The financial benefits of game use can be improved by developing expertise, technology, and marketing. Ecotourism is not well developed in the Eastern Cape although the Addo Elephant National Park is a financial success and provides considerable employment benefits within an ecologically sustainable system. The density of black rhinoceros and elephant in these thickets is among the highest in Africa, with high population growth and the lowest poaching risk. The financial and ecological viability of ecotourism and the conservation status of these two species warrant expanding ecotourism in the Eastern Cape, thereby reducing the probability of further degradation of ECST.

Seed removal by rodents, birds and ants in the semi-arid Karoo, South Africa

Removal rates of non-native seeds by small mammals, birds and ants were measured seasonally at two localities in the semi-arid Karoo, South Africa. Ants were the most important seed removers, with rodents removing lesser amounts of seed, and birds the least; however birds are probably underrepresented by this technique. Patterns of seed removal by small mammals in the Karoo contrast those in Israeli and North American deserts, and are convergent with those in Australian and South American deserts, despite the Karoo rodent fauna having taxonomic and morphological affinities with that of Israeli and North American deserts, respectively. It is suggested that these differences in the patterns of granivory are a result of environmental and possibly palaeoclimatic differences between the different deserts.

TIERBERG KAROO RESEARCH CENTRE: HISTORY, PHYSICAL ENVIRONMENT, FLORA AND FAUNA

SUMMARY The Tierberg Karoo Research Centre near Prince Albert in the southern Karoo is intended for long-term ecological monitoring and manipulative studies. This paper summarizes information on the management history, geology, soils, climate and vegetation and includes preliminary checklists of 189 vascular plant species, 25 ant, 90 bird, 18 reptile and 18 mammal species known to occur on the 1 km2 study site. In comparison with arid shrublands in North America, Australia. Israel and elsewhere in southern Africa, grasses and annual forbs are scarce, succulents abundant and there are few alien taxa.

The effects of vehicular and pedestrian traffic on dune vegetation in South Africa

Abstract The effects of varying intensities of off-road vehicle and pedestrian traffic on vegetation height and percent-cover were investigated at two sites representing pioneer and climax dune shrubland communities in South African dune systems. In all cases, a decreasing trend in vegetation height and percentage cover subsequent to application of the treatments was evident, although this was more clear in the shrub than in the pioneer community. The impact on vegetation variables increased with increasing intensity of vehicle and pedestrian treatments. Vehicles driven along a curved path resulted in greater vegetation destruction than those driven along a straight path. High intensity (single application) treatments resulted in an initial decrease in vegetation height and cover immediately after the impact, which was followed by a further decline over the next 3 months. This two-step response was attributed to the subsequent gradual death of the vegetation which was not evident immediately following the impact. Due to their faster growth rate, pioneer dune communities appear to have the capacity to recover following impacts, while dune shrub communities tend to be more vulnerable, exhibiting signs of damage for longer periods. The results of this study have value for managers of coastal dune systems, particularly those impacted by human recreational activities.

Impact of Grazing and Desertification in the Chihuahuan Desert: Plant Communities, Granivores and Granivory

Abstract Livestock effects on plant communities through overgrazing (desertification) should affect the structure and functioning of semarid rangeland communities. We measured plant, granivorous ant and rodent communities and rates of seed removal by rodents and ants in grazed (by livestock) and ungrazed desert grasslands as well as mesquite and creosotebush shrublands to test hypotheses on the effects of grazing and desertification on ecosystem structure and functioning. In desert grasslands grazing reduced the cover of perennial grasses, particularly the dominant Bouteloua eriopoda, but the cover of forbs and shrubs did not differ between treatments. One species of perennial grass, Dasyochloa pulchellum, increased in grazed grasslands compared with grassland exclosures. Detrended correspondence analysis showed that grazing caused desert grasslands to shift in community structure towards the shrublands. There were more seed harvesting ant and rodent species in the creosotebush shrublands than in the grasslands and mesquite shrublands. Grazing had no effect on the diversity of ants or rodents within grasslands, and detrended correspondence analysis revealed no clear trends in granivorous ant community structure in the grazed and ungrazed grasslands or the mesquite and creosotebush shrublands. Ants removed more seeds than did rodents in the grassland sites but rodents removed more seeds than did ants in the creosotebush sites and seed removal rates by rodents and ants were the same in the mesquite sites. Our data support the hypothesis that livestock grazing leads to a shift from grassland to shrubland in the Chihuahuan Desert, with associated changes in the structure and functioning of faunal communities. Because grasslands support few species and low densities of rodents, seed harvesting ants are the most important granivores in these desert grasslands. On a larger scale, we therefore hypothesize that the observed dominance of rodents as seed harvesters in the Chihuahuan desert is a function of the desertification of desert grasslands to shrublands by livestock, and that associated feedback effects may complicate the regeneration of degraded communities.

Mechanisms for the keystone status of kangaroo rats : graminivory rather than granivory ?

Abstract Graminivory by kangaroo rats (Dipodomys spp.) was investigated as a potential mechanism for the keystone role of these rodents in the dynamics of desert grasslands. Experiments confirmed that Ords kangaroo rats (Dipodomys ordii) cut and consumed a large proportion of the tillers of three Chihuahuan Desert tussock-forming grass species. Field observations indicated that the characteristically cut grass tillers were absent from all-rodent and medium-sized kangaroo rat exclosures, but were frequent in large-sized kangaroo rat and rabbit exclosures, indicating that the medium-sized kangaroo rats (D. ordii, D. merriami) were responsible for grass cutting. Tiller waste as a percentage of peak standing crop ranged from 7% in grassland habitats to 0.7% in Flourensia cernua shrubland. Of the 13 species of perennial, tussock-forming grasses measured, only one, Muhlenbergia porteri, had no tillers cut by kangaroo rats. This study demonstrates that the keystone role of kangaroo rats in Chihuahuan Desert grassland ecosystems is probably the result of their graminivory.

The effect of plant spinescence on the foraging efficiency of bushbuck and boergoats: browsers of similar body size

Abstract Thorn removal experiments quantified the effects of plant spinescence on the foraging efficiency of two mammalian browsers of similar body size, the indigenous bushbuck and the introduced domestic boergoat. Spinescence limited the intake rates of both browsers; the extent being influenced by the animals feeding technique. Larger bite sizes and rates enabled the bushbuck to increase their intake rate from dethorned branches. Spinescence restricted the feeding style of boergoats. Following thorn removal they attained larger bite sizes, and therefore greater intake rates. Boergoats were intrinsically fast eaters and were more efficient than bushbuck when foraging on spinescent species.

Human activity and potential impacts on dune breeding birds in the Alexandria coastal Dunefield

Abstract Human use of coasts has increased considerably with increasing demand for recreational experiences, increased availability of off-road vehicles (ORVs) and population increase. Besides impacts on dune morphology and flora, humans and ORVs also affect the fauna. The Alexandria Dunefield in Algoa Bay comprises a 50 km sandy beach backed by a 2.1 km wide strip of dunefield. The dunefield is largely conserved, but access to the beach is allowed under permit, and the beach is heavily utilised by fishermen and recreational ORV drivers. The area is also important for dune breeding birds. Beach and dune use by fishermen and other users was quantified by recording their position relative to the high water mark and along a 20 km stretch of beach, and through analysis of access permits and angling competition data. An increase in vehicle use in the area was observed. An indication of human perception of the area was obtained by questionnaires. Eighty percent of human activity was concentrated in 50% of the study site where the highest concentration of dune breeding birds nest. Sixty percent of the vehicles recorded, were on or above the high water mark (in the dunes). Of the beach-users interviewed, 74% suggested that only registered vehicles should be allowed on the beach. Most (80%) anglers had no problem determining the position of the high water mark. There is an overlap in area and seasonal use between beach-users and breeding birds. With specific areas along the beach being heavily impacted and vehicles utilising the area above the high water mark the potential for impact on the fauna and flora of these areas is high. There is a need to educate beach users as to the vulnerability of dune systems and to develop appropriate management guidelines to minimise the impacts of beach users on the dune fauna.