The importance of seed dispersal in the Alexandria Coastal Dunefield, South Africa

The endozoochorous dispersal of seeds by mammals and birds between distinct vegetation communities was assessed to determine the importance of these processes in coastal dune field management. Isolated pockets of thicket vegetation (bush-pockets) within a large coastal dune field provided the opportunity to study vertebrate seed dispersal and its contribution to their origin and maintenance. Mammalian and avian faeces were collected for the quantification of seeds dispersed via endozoochory. Birds and mammals showed considerable overlap, dispersing intact seeds of 17 and 29 plant species, respectively, but mammals dispersed a greater diversity and size range than birds. Extrapolation of mammalian faecal data indicates an annual input of 23 million intact seeds to the dune field. Significantly more seeds are deposited by mammals and birds in the bush-pockets than on open sand, and birds deposited greater numbers of seeds nearer the seed source. Zoochory appears to be critical for the maintenance of the bush-pocket habitats through the dispersal of climax woody plant species into the dune field. Directional dispersal by birds and mammals to the bush-pockets is considered to be responsible for the maintenance and possible origin of these bush-pockets. The high number of exotic plant propagules dispersed by both avian and mammalian zoochory highlights the importance of management of the Alexandria Coastal Dunefield (ACD) beyond the reserve boundaries. In a dynamic system such as the ACD which is within a declared nature reserve, the continued existence of the bush-pockets may depend on the maintenance, beyond the reserve boundaries, of a reservoir of not only plant material but vertebrate dispersers as well.     

耕地质量监测中合理样本量配置及不确定性分析——以陕西省宝鸡市为例

耕地质量监测样本量的优化配置对降低成本,实现可持续土地资源监测与利用有重要指导价值。以陕西省宝鸡市为例,采用2018年耕地质量监测数据,运用传统统计学和地统计学方法,探讨耕地质量监测中土壤监测指标的合理样本量及不确定性。研究表明：样本变异性大小与样本量的关系并不是绝对的。样本代表性评价方法和地统计学方法较Cochran方法能有效降低样本的不确定性;样本代表性评价法适用性更广,但研究结果缺乏稳定性;地统计学方法的适用性存在局限性,可降低中等变异性指标的不确定性,但对低、高变异性指标适用性较低。中等变异性指标宜采用地统计学方法确定合理样本量;低、高变异性指标宜采用代表性评价方法确定合理样本量。     

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.     

Deconstructing compassionate conservation

Compassionate conservation focuses on 4 tenets: first, do no harm; individuals matter; inclusivity of individual animals; and peaceful coexistence between humans and animals. Recently, compassionate conservation has been promoted as an alternative to conventional conservation philosophy. We believe examples presented by compassionate conservationists are deliberately or arbitrarily chosen to focus on mammals; inherently not compassionate; and offer ineffective conservation solutions. Compassionate conservation arbitrarily focuses on charismatic species, notably large predators and megaherbivores. The philosophy is not compassionate when it leaves invasive predators in the environment to cause harm to vastly more individuals of native species or uses the fear of harm by apex predators to terrorize mesopredators. Hindering the control of exotic species (megafauna, predators) in situ will not improve the conservation condition of the majority of biodiversity. The positions taken by so-called compassionate conservationists on particular species and on conservation actions could be extended to hinder other forms of conservation, including translocations, conservation fencing, and fertility control. Animal welfare is incredibly important to conservation, but ironically compassionate conservation does not offer the best welfare outcomes to animals and is often ineffective in achieving conservation goals. Consequently, compassionate conservation may threaten public and governmental support for conservation because of the limited understanding of conservation problems by the general public.     

Spatial and temporal changes in group dynamics and range use enable anti-predator responses in African buffalo

The reintroduction of large predators provides a framework to investigate responses by prey species to predators. Considerable research has been directed at the impact that reintroduced wolves (Canis lupus) have on cervids, and to a lesser degree, bovids, in northern temperate regions. Generally, these impacts alter feeding, activity, and ranging behavior, or combinations of these. However, there are few studies on the response of African bovids to reintroduced predators, and thus, there is limited data to compare responses by tropical and temperate ungulates to predator reintroductions. Using the reintroduction of lion (Panthera leo) into the Addo Elephant National Park (AENP) Main Camp Section, South Africa, we show that Cape buffalo (Syncerus caffer) responses differ from northern temperate ungulates. Following lion reintroduction, buffalo herds amalgamated into larger, more defendable units; this corresponded with an increase in the survival of juvenile buffalo. Current habitat preference of buffalo breeding herds is for open habitats, especially during the night and morning, when lion are active. The increase in group size and habitat preference countered initial high levels of predation on juvenile buffalo, resulting in a return in the proportion of juveniles in breeding herds to pre-lion levels. Our results show that buffalo responses to reintroduced large predators in southern Africa differ to those of northern temperate bovids or cervids in the face of wolf predation. We predict that the nature of the prey response to predator reintroduction is likely to reflect the trade-off between the predator selection and hunting strategy of predators against the life history and foraging strategies of each prey species.     

Biotic processes in a coastal dunefield: An assessment of seed removal, with non-native seed removal experiments

The impact of granivores on coastal dune seed reserves may be high, increasing along a landward gradient from the littoral zone as the structural complexity of the habitat increases. Seasonal removal rates of non-native seeds by nocturnal and diurnal vertebrates and ants from experimental seed trays in two habitats within the Alexandria Coastal Dunefield, South Africa, were determined. Overall, seed removal was higher in the dune-field bush-pocket habitat than the landward thicket habitat. Nocturnal vertebrates were the most important seed removers within bush-pockets. The importance of nocturnal vertebrates decreased in the thicket and there was a shift in the dominant seed removers to diurnal vertebrates. Seed removal by ants and diurnal vertebrates did not differ significantly between the bush-pockets and thicket while that of nocturnal vertebrates showed a significant change. This can be ascribed to the abundance of the omnivorous murid rodentGerbillurus paeba exilis in the bush-pockets which is absent from thicket vegetation.     

Patterns of development and succession of vegetated hummocks in slacks of the Alexandria coastal dune field, South Africa

Dune hummocks (small aeolian dunes formed by sand deposition in and around pioneer plants) are the smallest vegetated dune unit; they occur along the entire South African coastline but are poorly studied. Structural properties and distribution of the two main hummock-forming plants:Arctotheca populifolia (a pioneer species with fast growth rate and rapid turnover) andGazania rigens (a later colonizer with slower growth) were investigated. A marked vegetation succession exists across the floor of the slack as a result of the migration of transverse dune ridges across the slack.Arctotheca hummocks were initiated on the newly exposed eastern margin of the slack, and were replaced about midway across the width of the slack byGazania hummocks. Hummocks increased in size with distance from the eastern side of the slack.Gazania hummocks attain a greater vegetation height, support a greater vegetation complexity and mass, and attain a larger maximum size thanArctotheca hummocks. Succession, defined as both the replacement of plant species as well as site modification within the plants over time, was evident. Since the growth form and dynamics determine (1) the ability of plants to trap wind-borne soil and detritus, (2) the shape of the hummocks, and (3) the habitat complexity available to spiders and insects, the ecology of the hummocks is probably determined largely by the vegetation characteristics of the hummock-forming plants.