关键词： competition   herbivory   resource availability   tree seedling establishment  

摘要： 1 We studied the establishment of tree seedlings in Mediterranean-type old fields in South Australia in different biotic environments and under different levels of resource availability. Specifically we wanted to: (a) test for a logarithmic relationship between the relative intensity of competition (RCI) and resource availability;(b) assess the potential of confounding resource competition with invertebrate herbivory;and (c) assess whether the architecture of the plant community had any qualitative or quantitative effects upon the relationship between resource availability and RCI. 2 Our glasshouse experiment showed that RCI increased with resource availability at low levels of resources, but not at higher levels, consistent with a logarithmic relationship. 3 The effects of resource competition and invertebrate herbivory were heavily confounded in the field experiment. 4 Plant architecture significantly affected the behaviour and abundance of invertebrates and we therefore conclude that it has the potential to modify the relationship between resource availability and competitive intensity. 5 Although the habitat templet/C-S-R model appears reasonably robust, modification of its general framework may be required because one of its basic underlying assumptions is most accurate when competition is defined phenomenologically.

关键词： Castanopsis sempervirens   chinquapin   food hoarding   granivory   scatterhoarding   secondary seed dispersal  

摘要： Seed dispersal often occurs in two or more discrete stages, but the effects of the latter stages of dispersal on successful recruitment have seldom been measured. We investigated the relative contributions of primary and secondary seed dispersal of Sierra bush chinquapin (Castanopsis sempervirens;Fagaceae) to seedling establishment. Rodents (mostly yellow pine chipmunks, Tamias amoenus) harvested chinquapin nuts rapidly during a three-week period starting in mid-August and scatterhoarded most nuts (81%) in the ground. Most initial (primary) caches contained one nut (range = 1-5 nuts) buried 10-23 mm deep within 46 m of source shrubs. Rodents subsequently retrieved 95% of these nuts and recached at least 33% elsewhere (secondary caches), at,lower densities and up to 64 m from source plants. By winter, 41% and 21% of nuts harvested from shrubs remained in scatter caches in 1999 and 2000, respectively. Only 10 caches (4 primary and 6 secondary caches) present in winter 1999 (7.8%), and no caches from winter 2000, produced seedlings the following spring. All seedlings died during the first growing season because of rodent grazing and desiccation. Despite low seedling survival in this study, chinquapin appears to be dependent upon scatterhoarding rodents for seedling recruitment. Secondary dispersal is an important aspect of chinquapin dispersal. Secondary caches contributed more to chinquapin seedling recruitment than primary caches;2.5% of primary caches and 5.6% of secondary caches produced seedlings. This study suggests that, for propagules that move repeatedly during dispersal, a clear understanding of the dynamics of seed dispersal can be gained only by following seed movements, determining the transition probabilities between different stages of dispersal, and assessing the contribution of each stage of seed dispersal to plant recruitment.

关键词： banner-tail kangaroo rats   black-grama grasslands   Bouteloua eriopoda   fire   germination   heteromyid rodents   mesquite   Prosopis glandulosa  

摘要： We conducted experiments to examine microsite and rodent influence on mesquite (Prosopis glandulosa) germination and survival in Chihuahuan Desert black-grama (Bouteloua eriopoda) grassland. Simulated caches with mesquite seeds were placed in undisturbed grassland, burned grassland patches with reduced grass cover, and on the periphery of kangaroo rat mounds. Rodent access to cached seeds was controlled by covering half of the caches with mesh domes. Kangaroo rats destroyed citing pats containing scarified mesquite seeds and excavated all seeds in simulated caches during a year in which no grasses or forbs set seed. Germination was the highest ill unburned grassland, but over-winter survival was only observed across experiments in burned grassland microsites. A large proportion of seed caches were excavated (1.1-5.5% of the rodent-excluded caches and between 15.6% and 21.1% of the control caches). There were seasonal differences in numbers of emergent seedlings, with a peak in September 2002 following late summer rains. There were no significant differences in numbers of germinants in burned and unburned grassland microsites, but significantly Fewer mesquite seeds germinated on banner-tail kangaroo rat Mounds. Caches excavated by rodents yielded 46.6% of germinants. This Study suggests that scarification of mesquite seeds is not necessary for germination and heteromyid rodents may be responsible for increased mesquite density in grasslands with some mature mesquite plants. The data also suggest that competition between mesquite seedlings and grasses in black-grama grassland is weak because of the physical characteristics of this system. (c) 2005 Elsevier Ltd. All rights reserved.

关键词： post-dispersal seed predation   pre-emptive competition   recruitment potential   seed limitation   seed traits  

摘要： We investigated the role of seed predation by rodents in the recruitment of the fleshy-fruited trees Taxus baccata, Ilex aquifolium and Crataegus monogyna in temperate secondary forests in NW Spain. We measured the densities of dispersed seeds, early emerged seedlings, established recruits and adults, at four sites over a period of 2 years. Seed predation among species was compared by seed removal experiments and analysis of rodent larder-hoards. The three species differed markedly in local regeneration patterns. The rank order in the seed rain following decreasing seed density was flex, Taxus and Crataegus. However, Crataegus established 3.3 times more seedlings than Taxus. For all species, there was a positive linear relationship between the density of emerged seedlings and seed density, suggesting that recruitment was seed-rather than microsite-limited. A consistent pattern of seed selection among species was exerted by rodents, which preferred Taxus and, secondarily, flex seeds to Crataegus seeds. Predation ranking was the inverse of that of seed protection against predators, measured as the mass of woody coat per mass unit of the edible fraction. Recruitment potential, evaluated as the ratio of seedlings to seeds, was negatively related to seed predation, with the rank order Crataegus>Ilex>Taxus. The selective early recruitment limitation exerted by predation may have a demographic effect in the long term, as judged by the positive relationship between early seedling emergence and the density of established recruits. By modulating the pre-emptive competition for seed safe sites, rodents may preclude the progressive exclusion of species that produce low numbers of seeds (i.e. Crataegus) by those dominant in seed number (i.e. flex, Taxus), or at least foster the evenness for site occupation among seedlings of different species.

关键词： Amazonian savanna   soil invertebrate   habitat specificity   edaphic factors   vegetation structure  

摘要： Using ordinations techniques, we investigated the effects of different types of plant cover on the relationship between soil structure and invertebrate communities in an Amazonian savanna. Vegetation islands were chosen where four selected shrubs species were present on sandy and clayey soils. For each sample under a selected shrub within the clump, another sample was taken in the grass-tuft and extracted in Berlese-Tullgren. Classifying at higher taxonomic levels, we detected 27 zoological categories. The mean number of individuals was generally higher on shrubs. Acari and Collembola were the dominant groups. Non-Oribatid mites dominated in the savanna, in contrary with what occurs in most Amazonian ecosystems, where the dominance of Oribatida is always higher than others Acari. The level of taxonomic resolution utilized was sufficient to show the main differences of the spatial variation in community structure. We detected effects of soil type, vegetation structure and plant specie identity on the composition of the communities. The mesofauna have a mosaic distribution in the savanna dependent on the soil-food web structure of the vegetation. Shrubs and grass-tuft generate different ecosystems. Therefore, studies with better taxonomic resolution will be necessary to assess the magnitude of the effect of biotic and abiotic factors. (C) 2005 Elsevier B.V All rights reserved.

关键词： AGALYCHNIS   EMBRYOS   RISK management in business   EGGS -- Incubation  

摘要： I examined the role of vibrations in predator-induced early hatching of red-eyed treefrogs, Agalychnis callidryas. The arboreal eggs of A. callidryas hatch up to 30% early if attacked by egg-eating snakes. This induced hatching is a behavioural response that occurs once snakes begin physically disturbing the clutch, and is sufficiently rapid to allow most embryos to escape. Other intense but benign disturbances, such as tropical storms, do not induce such hatching. I used a miniature accelerometer to record vibrations in egg clutches during snake attacks and rainstorms, and analysed the recordings to identify parameters that distinguished disturbance types. Snake-induced vibrations were on average longer, more widely spaced, and of lower frequency than rain-induced vibrations. I performed three sets of vibration playbacks to examine the hatching response of embryos to different vibration patterns. (1) Playbacks of recorded snake attacks elicited more hatching than did rain recordings. (2) 1 edited snake and rain recordings by moving periods of stillness to clump together rain vibrations and extend intervals, and divide snake vibrations into shorter, more tightly spaced bits. In playbacks, clumped rain elicited more, and divided snake vibrations less hatching than did the original recordings. (3) Bursts of white noise with a constant vibration-to-interval ratio but different cycle durations elicited different levels of hatching. Vibrations alone were sufficient to induce early hatching, without chemical or visual cues from predators. Embryos also clearly distinguished among different vibration patterns and used cues in the gross temporal pattern in making their hatching decision. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

关键词： 土壤动物群落   枸树   集聚   凋落物分解   百望山  

摘要： 20 0 2年4～1 1月,采用凋落袋法(5mm、1mm和1 3 0 0mm)对北京百望山土壤动物群落结构在枸树(Broussonetiapapyrifera)凋落叶分解过程中的动态变化进行了研究。在5 6只分解袋中,共采集到土壤动物3 3 2 2只(未知1 7只) ,隶属5门1 2纲2 5目1 9科,其中摇蚊科(Chironomidae)、盲蛛目(Opiliones)、圆跳科(Sminthuridae)、等节跳科(Isotomidae)、棘跳科(Onychiuridae)、长角跳科(Entomobryidae)、蜱螨目(Acariformes)为优势类群。土壤动物以杂食性和植食性为主。3种凋落袋中,土壤动物总类群数和个体总数均5mm >1mm >1 3 0 0mm ,并且前两者分别在1 0月份或7月份达到最大值。土壤动物多样性随月份变化幅度较大,多样性变化与反映群落变化的个体数量、类群数以及均匀性指数的变化不一致。鼠妇科(Porcellionidae)在凋落物中集聚的时间最长,后孔寡毛目(Oligochaetaopisthopora)集聚的时间最短,分别为1 2 48和8 0 0个月。

关键词： fire   herbivores   micronutrients   savanna   soils   vegetation cover  

摘要： Despite decades of research, the primary factors determining savanna structure remain elusive - a conundrum termed 'the savanna problem'. After 47 years of annual burning in Terminalia woodland and Acacia/Combretum savanna on sandy, granite-derived soils in the southern Kruger National Park, South Africa, a dense cover of trees and shrubs persists on some burnt plots and is largely absent from others. We postulated that intense browsing pressure by antelope and other herbivores prevents recruitment of trees in burnt plots and that herbivores concentrate on plots that are richest in nutrients. Herbivore abundance did not show a relationship with soil macronutrients and we consequently investigated micronutrient status. The reduction in tree cover as a result of annual burning was positively correlated with mass of herbivores (15-1500 kg) (r (2) = 0.61, n = 8). This index of herbivore abundance was in turn positively correlated with total Zn (r (2) = 0.64, n = 8). Other indices of herbivore abundance showed significant relationships with total clay content and total Mn. We suggest that herbivores concentrate on sites with greater clay content (possibly due to a greater availability of micronutrients), and that tree cover can remain relatively dense under a regime of annual burning if browsing pressure is not intense. The long-term burn experiments in the Kruger National Park savanna provide a platform for unravelling the savanna problem. Determining possible interactions between soil properties, herbivory and fire is a step in this direction.

关键词： HABITAT (Ecology)   HERBIVORES   FOREST fires   SAVANNA animals   VEGETATION & climate   ANIMAL feeding  

摘要： Discusses studies on resprouting vegetation initiated by fire, and reinforced by herbivory. Attraction of herbivores to the same areas in a feedback loop; Examination of the habitat after burning occurred; Test of whether herbivores prefer burnt areas in subsequent growing seasons.

关键词： ARTHROPODA   LAND settlement   BIOTIC communities   EARTH (Planet)   CRUST  

摘要： The colonization of continental environments (land and fresh water) has focused historically on a major event during the mid-Paleozoic Era characterized by the relatively sudden emergence of megascopic embryophytes, fungi, arthropods and tetrapods. A significant earlier phase of Precambrian (Archean and Proterozoic Eons) terrestrialization extends to the first 80% of the history of life and records the colonization of subaerial soils or rock surfaces predominantly by cyanobacterial mats and crusts. These two phases are separated by a similar to 90-million-year early Paleozoic interlude of minimal terrestrial colonization. Trophically modern ecosystems appeared during the Late Silurian-Middle Devonian (425-375 million years ago), consisting of complex symbiotic, parasitic and other trophic associations, including detritivory and limited herbivory. The integration of these two historically disparate fields (Precambrian microorganisms and their biochemical and sedimentological signatures, and the paleoecology of mid-Paleozoic ecosystems) has resulted in a wider perspective on terrestrialization. Here, I present an ecological and evolutionary context for the emergence of terrestrial ecosystems and examine associations among organisms, from the endosymbiotic capture of organelles by eukaryotes to modes of metazoan nutrition on land. Such studies now enable the tracking, in ecological detail, of the invasion of continental environments during the past 3.5 billion years of life.