Task selection by workers of the fire ant Solenopsis invicta

The effects of worker size, age, and crop fullness on the flow of food into the colony were assessed using video recording and playback. Regardless of the level of colony satiation, small workers seldom had full crops and were more involved in larval grooming than in food traffic. Large workers played little role in larval care, but tended to be recruited easily to a food source and to store food in their crops. Medium workers had crops ranging from empty to full because they alternated between ingesting from and donating food to other colony members. Medium workers were the most versatile, engaging competently in food recruitment, larval grooming, and larval feeding. They displayed considerable variation in the frequency at which they fed larvae: some fed a few larvae before switching to other tasks, others fed over a hundred larvae before switching. The persistence, or lack thereof, of a worker's feeding response suggests a flexibility unaccounted for by the fixed-threshold-response hypothesis. Worker coverage of the brood pile was a dynamic equilibrium process unaffected by worker size, age, or crop fullness, or by differences in the nutritional or hygienic states of larvae. In summary, it appeared that worker size and age offered coarse regulation of task selection by workers, whereas crop fullness, flexible response, and task switching fine-tuned task selection. Received: 25 May 1998 / Accepted after revision: 20 August 1998     

Vulnerability and Resilience of Tropical Forest Species to Land‐Use Change

Abstract: We provide a cross‐taxon and historical analysis of what makes tropical forest species vulnerable to extinction. Several traits have been important for species survival in the recent and distant geological past, including seed dormancy and vegetative growth in plants, small body size in mammals, and vagility in insects. For major past catastrophes, such as the five mass extinction events, large range size and vagility or dispersal were key to species survival. Traits that make some species more vulnerable to extinction are consistent across time scales. Terrestrial organisms, particularly animals, are more extinction prone than marine organisms. Plants that persist through dramatic changes often reproduce vegetatively and possess mechanisms of die back. Synergistic interactions between current anthropogenic threats, such as logging, fire, hunting, pests and diseases, and climate change are frequent. Rising temperatures threaten all organisms, perhaps particularly tropical organisms adapted to small temperature ranges and isolated by distance from suitable future climates. Mutualist species and trophic specialists may also be more threatened because of such range‐shift gaps. Phylogenetically specialized groups may be collectively more prone to extinction than generalists. Characterization of tropical forest species’ vulnerability to anthropogenic change is constrained by complex interactions among threats and by both taxonomic and ecological impediments, including gross undersampling of biotas and poor understanding of the spatial patterns of taxa at all scales.     

Interactions between Ecological Traits and Host Plant Type Explain Distribution Change in Noctuid Moths

Abstract:  The ecological traits of species determine how well a species can withstand threats to which it is exposed. If these predisposing traits can be identified, species that are most at risk of decline can be identified and an understanding of the processes behind the declines can be gained. We sought to determine how body size, specificity of larval host plant, overwintering stage, type of host plant, and the interactions of these traits are related to the distribution change in noctuid moths. We used data derived from the literature and analyzed the effects of traits both separately and simultaneously in the same model. When we analyzed the traits separately, it seemed the most important determinants of distribution change were overwintering stage and type of host plant. Nevertheless, ecological traits are often correlated and the independent effect of each trait may not be seen in analyses in which traits are analyzed separately. When we accounted for other correlated traits, the results were substantially different. Only one trait (body size), but 3 interactions, explained distribution change. This finding suggests that distribution change is not determined by 1 or 2 traits; rather, the effect of the traits depends on other interacting traits. Such complexity makes it difficult to understand the processes behind distribution changes and emphasizes the need for basic ecological knowledge of species. With such basic knowledge, a more accurate picture of the factors causing distribution changes and increasing risk of extinction might be attainable.     

山西历山山地草甸生物多样性、优势种和土壤因素对群落生产力的影响

自然生态系统生产力同生物多样性、优势种功能性状和土壤性质等多因素紧密关联,因此,受到多变量过程的综合调控。利用结构方程模型研究了山西历山山地草甸物种多样性、功能多样性、优势种功能性状和土壤等多变量因素对群落生产力的影响。结果表明：除了物种多样性外（γ=0.10,P=0.69）,优势种功能性状（γ=0.61,P=0.00）、功能多样性（γ=0.47,P=0.04）和土壤因素（γ=0.34,P=0.02）直接影响群落生产力,并且土壤因素还通过改变优势种功能性状和功能多样性的方式间接影响群落生产力（间接影响系数分别为0.35、0.27）。优势种功能性状是预测群落生产力变化的最佳变量,其次是功能多样性和土壤因素。因此,理解自然生态系统生产力变化应在引入多元方法的前提下,重点考虑优势种功能性状因素。     

两种生物炭对烤烟生长、根际土壤性质和微生物群落结构的影响

为探明生物炭对烤烟生长影响的作用机理,选取小麦秸秆炭(WB)和烟杆炭(TB)为试验材料,以不添加生物炭处理CK为对照,采用盆栽试验,研究两种生物炭对团颗期烟草的农艺性状和根际土壤理化性质及微生物群落结构的影响.结果表明:与CK处理相比,WB和TB处理烟草的地上部干重分别增加4.4和4.7倍,土壤硝态氮含量分别降低64.7%和47.6%,脱氢酶活性降低56.4%和48.7%.WB和TB两处理土壤细菌和真菌的Shannon和Simpson多样性指数及Chao1丰富度指数均显著降低,细菌的OTUs数分别显著减小20.6%和18.0%,真菌的OTUs数分别显著减小53.8%和77.4%.细菌优势菌种中,WB处理放线菌门相对丰度提高69.5%,TB处理Saccharibacteria的丰度提高129.7%,WB和TB处理疣微菌门丰度分别降低37.6%和40.9%.真菌优势菌种中,TB处理子囊菌门丰度提高133.8%,WB和TB处理接合菌门的丰度分别降低87.5%和92.9%.通过β多样性分析可知,烟杆炭对烤烟根际土壤微生物群落结构的影响大于小麦秸秆炭.     

Functional traits of poplar leaves and fine roots responses to ozone pollution under soil nitrogen addition

Concurrent ground-level ozone（O₃） pollution and anthropogenic nitrogen（N） deposition can markedly influence dynamics and productivity in forests.Most studies evaluating the functional traits responses of rapid-turnover organs to O₃ have specifically examined leaves,despite fine roots are another major source of soil carbon and nutrient input in forest ecosystems.How elevated O₃ levels impact fine root biomass and biochemistry remains to be resolved.This study was...     

Effects of embryonic exposure to conspecific chemical cues on hatching and larval traits in the common frog <Emphasis Type="Italic">(Rana temporaria)</Emphasis>

Summary. Recent studies indicate that amphibian eggs are capable of hatching plasticity in response to chemical cues released by predators feeding on conspecific eggs or larvae. However, information is scarce on the relative importance of predator and conspecific cues in such a process. In particular, no attempt has been made to compare the effects of embryonic exposures to chemical cues indicative of a predation risk for eggs and larvae, although both life stages can co-occur in natural habitats. In this context, common frog embryos (Rana temporaria) were raised until hatching in the presence of crushed conspecific extracts from eggs and tadpoles to assess their respective influences on some hatching and larval traits. While a significant delay in hatching time was observed in embryos exposed to chemical cues from tadpole extract, this life-history shift appeared unaffected by embryonic exposure to egg extract. Hatchlings derived from eggs incubated in the presence of both conspecific extracts showed a significantly greater weight than unexposed controls. However, such an effect was no longer apparent 15, 30 and 50 days after hatching, suggesting that embryonic exposure to chemical cues from damaged conspecific eggs and tadpoles has no influence on larval growth. Lastly, morphological measurements performed on hatchlings and older tadpoles (15, 30 and 50 days old) revealed no significant effect of embryonic treatments on the shape of body and tail.     

Environmental variability and allocation trade-offs maintain species diversity in a process-based model of succulent plant communities

Ecological theory suggests that environmental variability can promote coexistence, provided that species occupy differential niches. In this study, we focus on two questions: (1) Do allocation trade-offs provide a sufficient basis for niche differentiation in succulent plant communities? (2) What is the relative importance of different forms of environmental variability on species diversity and community composition? We approach these questions with a generic, individual-based simulation model. In our model, plants compete for water in a spatially explicit environment. Species differ in their size at maturity and in the allocation of carbon to roots, leaves and storage tissue. The model was fully specified with independent literature data. Model output was compared to characteristics of a species-rich community in the semi-arid Richtersveld (South Africa). The model reproduced the coexistence of plants with different sizes at maturity, the dominance of succulent shrubs, and the level of vegetation cover. We analyzed the effects of three forms of environmental variability: (a) temporal fluctuations in precipitation (rain and fog), (b) spatial heterogeneity of water supply due to run-on and run-off processes and (c) ‘rock pockets’ that limit root competition in space. The three types of variability had differential effects on diversity: diversity exhibited a strong hump-shaped response to temporal variation. Spatial variability increased diversity, with the strongest increase occurring at intermediate levels of temporal variability. Finally, rock pockets had the weakest effect, but contributed to diversity by providing refuges for small species, particularly at low temporal variability. The model thus shows that spatio-temporal variation of resource supply can maintain diversity over long time scales even in small systems, as is the case in the Richtersveld succulent communities. Trade-offs in allocation provide the basis for necessary niche differentiation. By describing resource competition between individual plants, our model provides a mechanistic basis for the link from species traits to community composition at given environmental conditions. It thereby contributes to an understanding of the forces shaping plant communities. Such an understanding is critical to reduce the threats environmental change poses to biodiversity and ecosystem services.     

A dynamic trait affects continuous pair assessment in the blue-footed booby,<Emphasis Type="Italic"> Sula nebouxii</Emphasis>

Bright colours of male birds have often been shown to be the target of sexual selection through female choice, yet few studies have looked at the role of colour expressed after pairing on female motivation and behaviour. Here we analyse the role of an integumentary colour in the spectral range of 400–700 nm, the foot colour in male blue-footed boobies, Sula nebouxii, which is prominently displayed during pair courtship. Measurements early in the breeding season showed that foot colour of courting males is pale (high values of brightness) and has an aqua-blue chroma, and females in better body condition were mated to males with brighter feet. We carried out an experimental manipulation which modified the foot colour of males in courtship, making it closer to the foot colour of males in low nutritional state. We found that females paired to experimental males courted less and were less likely to copulate than females in the control group. Male behaviour was apparently unaffected by the manipulation; thus the change in female behaviour can be attributed exclusively to foot colour manipulation. These results strongly support the hypothesis of female preference for an integumentary colour and suggest that this dynamic trait is used as a male ornament after pairing.Communicated by J. Graves     

污泥堆肥对几种花卉的生长响应研究

施用污泥堆肥后，木槿、月季、美人蕉及旱荷花的开花量增加，花期延长，金枣、龟背竹与五叶地锦的各生长参数也明显增大；土壤理化性质有明显改善；当污泥堆肥施用量小于９ｋｇ／ｍ＾２时，无因盐分、ＮＯ３＾－－Ｎ淋溶及地面径流而造成的环境问题。