Mopane diaspores are not dispersed by epizoochory

The mode of dispersal of the diaspores of Colophospermum mopane has always been ascribed to epizoochory due the slightly sticky nature of mopane diaspores. The stickiness results from the plentiful supply of resinous compounds in developing structures on a mopane plant. Epizoochory as the mode of dispersal for both seeds which had the pod removed and diaspores of C. mopane is disproved, and experimentation shows the most likely agents of dispersal of mopane diaspores to be water and wind.     

Passive external transport of freshwater invertebrates by elephant and other mud‐wallowing mammals in an African savannah habitat

1. Recent findings hint at the potential importance of mammals affecting the spatial dynamics of aquatic organisms in areas where mammals live in close association with water. Perhaps the most iconic example of such an environment is the African savannah. 2. We investigated dispersal patterns of freshwater organisms among a set of temporary ponds in SE Zimbabwe to test the hypothesis that large mammals, and particularly African elephants (Loxodonta africana), can be important vectors of aquatic organisms. Dispersal kernels were reconstructed by hatching mud collected from ‘rubbing’ trees located at increasing distances from a set of isolated ponds. To assess the relative importance of other mammalian vectors, the vertical distribution of mud on rubbing trees was mapped and related to the body size of candidate vector species. 3. Laboratory hatching of mud samples revealed large numbers of propagules of 22 invertebrate taxa as well as some aquatic macrophytes. Dispersing communities reflected source communities and diverged with increasing distance from the source. Both dispersal rates and richness of transported taxa decreased significantly with dispersal distance. No indications for differences in dispersal capacity among propagule types were detected. Instead, common propagules were more likely to travel greater distances. Most mud was attached to trees at heights >1.5 m, implicating elephants as the dominant vector. Vertical distributions of tree mud, however, also revealed clustering at heights up to 50 cm and 90–120 cm corresponding to the height of warthog, rhinoceros and buffalo, respectively. Finally, variation in the vertical distribution of mud on trees in combination with differences in vector vagility suggests that local differences in vector species composition may affect passive dispersal dynamics of aquatic organisms. 4. Based on vagility and vector load, mud‐wallowing mammals emerge as highly effective vectors that, in some areas, may be more important in transporting aquatic organisms than traditionally recognised vectors such as waterbirds. Since most large‐ and medium‐sized mammals currently have restricted geographic distributions, it is likely that mammal‐mediated dispersal was more important in the past.     

Epizoochorous dispersal by barbs, hooks, and spines in a lowland moist forest in central French Guiana

An analysis of the flowering plant flora of a lowland moist forest in central French Guiana reveals 25 species with adaptations for epizoochorous dispersal by barbs, hooks, or spines (stick-tights). This represents 1.5% of the flowering plant flora. Stick-tights are represented among the monocotyledons of the flora of central French Guiana by five species of Poaceae. The Fabaceae and Asteraceae, each with six species with stick-tight dispersal, are the richest families of flowering plants in terms of stick-tight dispersal in central French Guiana. This region possesses numerous potential mammal and bird dispersal agents, therefore it is a puzzle why stick-tight dispersal, especially among species of the canopy, is not more frequent.     

Dispersal of non-native plants by introduced bison in an island ecosystem

An understanding of the mechanisms of seed dispersal is critical to effectively managing populations of non-native plants. We investigated whether introduced bison on Santa Catalina Island, California, have the potential to spread non-native plants through the shedding of clumps of seed-laden hair and/or ingesting and later excreting seeds. We collected clumps of hair shaved from bison during a roundup and dislodged by wallowing activity. Greenhouse and field trials were used to test for seed viability and persistence of hair clumps in wallows. In addition to trials with bison hair, we collected samples of bison dung and tested for seed germination in a greenhouse. The majority of seeds extracted from bison hair clumps were of non-native forbs. There was a significant positive relationship between the size of hair clumps and the number of seeds extracted from the clumps, suggesting that managing the introduced bison population at a lower level will help minimize the spread of non-native plants by the species. Seeds of non-native plants were capable of germinating under conditions similar to those on Santa Catalina Island. Clumps of bison hair persisted in wallows, but did not remain intact and lost nearly 40% of their original mass. The number of germinable seeds contained in bison dung was low: 18 seeds germinated from 6 of 18 dung samples. Introduced bison appear to facilitate the dispersal of non-native plants over native plants on Santa Catalina Island. Our study suggests that a comprehensive strategy to control non-native plants must involve the management of the animal agents of plant dispersal.     

Fruit eating and seed dispersal by howling monkeys (Alouatta palliata) in the tropical rain forest of Los Tuxtlas,Mexico

The frugivory and ranging habits of howling monkeys living in the rain forest of Los Tuxtlas, Veracruz, Mexico, were studied for 5 consecutive years with the aim of investigating the role of seed dispersal agents played by the howling monkeys. The howling monkeys' consumption of fruit occupied half of their feeding time, and 80% of this time was spent feeding on mature fruit. Observations confirmed use of 19 tree species and a preference for a few species of Moraceae and Lauraceae. Fruit exploitation was very seasonal; only two species provided fruit year-round. Home range size was about 60 ha, and animals in the troop (N = 16) showed a day range of 10–893 m. Monthly collection of fecal samples during 2 years indicated that 90% of the seeds (N = 7,928) in the samples belonged to eight tree species and to one liana; the rest belonged to 15 unidentified species of vines. Germination success for the seeds in the feces was about 60% and for control seeds was 35%. Howling monkeys created diverse seed shadows in the vicinity of their leaf and fruit sources, and while they dispersed the seeds of some plant species, they also produced a great deal of fruit and seed waste for others.     

Peduncles elicit large-mammal endozoochory in a dry-fruited plant

Background and Aims

Plants have evolved a variety of seed dispersal mechanisms to overcome lack of mobility. Many species embed seeds in fleshy pulp to elicit endozoochory, i.e. disseminating seed through the animal gut. In contrast to well-studied fleshy fruited plants, dry-fruited plants may exploit this dispersal mutualism by producing fleshy appendages as a nutritional reward to entice animals to swallow their diaspores, but this has been little studied. In this study, it is hypothesized that these accessory fruits represent co-adaptations facilitating the syndrome of mammalian endozoochorous dispersal.

Methods

Field observations (focal tree watches, faecal surveys and fruiting phenology) with experimental manipulations (examination of seed germination and feeding trials) were conducted over 2 years in a native population of the raisin tree, Hovenia dulcis, which produces enlarged, twisted brown peduncles with external black seeds, in central China.

Key Results

Birds were not observed to swallow seeds or carry infructescences away during 190 h of focal tree watches. However, H. dulcis seeds were detected in 247 faecal samples, representative of two herbivore and four carnivore mammalian species. Feeding trials revealed that peduncles attracted mammals to consume the entire infructescence, thereby facilitating effective seed dispersal. The germination rate of egested seeds proved higher than that of unconsumed seeds. It was also noted that this mutualism was most vulnerable in degraded forest.

Conclusions Hovenia dulcis

peduncle sets are confirmed to adapt primarily to mammalian endozoochory, a mutualistic association similar in function to fleshy pulp or foliage. This demonstrates that plant organ systems can be adapted to unique mutualisms that utilize animal dispersal agents. Such an ecological role has until now been attributed only to bird epizoochory. Future studies should consider more widely the putative role of peduncle sets and mammalian endozoochory as a dispersal mechanism, particularly for those plants that possess relatively large accessory fruits.     

杂草种子传播研究进展

种子传播将母株生殖周期的末端与它们后代种群的建立连结了起来,广泛认为,其对植被结构具有深刻的影响。种子传播的整个过程称为种子传播循环。研究表明,杂草种子传播的因子多种多样,包括仅依赖自身来完成的主动传播,以及依赖风、水、动物、人类等外界媒介的被动传播。其中,人类传播杂草种子是影响最广泛的一种,对现代植物的分布格局产生了深刻的影响。杂草种子的传播,对杂草种子库的数量和空间动态影响很大。研究种子传播的主要方法有荧光染料标记法、放射性同位素标记法、稳定同位素分析、分子遗传标记等。结合近几年国内外的研究进展,作者就杂草种子传播对种子库数量和空间动态影响的精确直接研究、杂草种子传播的过程及传播后的命运、杂草种子适应传播的机理、生态控草措施研究、外来杂草入侵蔓延与其种子传播的关系等方面提出了展望。