The community matrix in three species community models

The explicit function of the community matrix of a three dimensional Lotka-Volterra model is delineated by a set of necessary and sufficient conditions for a positive equilibrium to be asymptotically stable. In the special case that the community matrix is quasi weakly diagonally dominant, it is shown that a positive determinant for the community matrix is not only necessary but is also sufficient for stability. The results are specific to three dimensional models and do not extend to communities of dimension greater than three.     

Is a community still a community? Reviewing definitions of key terms in community ecology

Community ecology is an inherently complicated field, confounded by the conflicting use of fundamental terms. Nearly two decades ago, Fauth et al. (1996) demonstrated that imprecise language led to the virtual synonymy of important terms and so attempted to clearly define four keywords in community ecology; “community,” “assemblage,” “guild,” and “ensemble”. We revisit Fauth et al.'s conclusion and discuss how the use of these terms has changed over time since their review. An updated analysis of term definition from a selection of popular ecological textbooks suggests that definitions have drifted away from those encountered pre‐1996, and slightly disagreed with results from a survey of 100 ecology professionals (comprising of academic professors, nonacademic PhDs, graduate and undergraduate biology students). Results suggest that confusion about these terms is still widespread in ecology. We conclude with clear suggestions for definitions of each term to be adopted hereafter to provide greater cohesion among research groups.     

Trade-offs in community properties through time in a desert rodent community

Resource limitation represents an important constraint on ecological communities, which restricts the total abundance, biomass, and community energy flux a given community can support. However, the exact relationship among these three measures of biological activity remains unclear. Here we use a simple framework that links abundance and biomass with an energetic constraint. Under constant energetic availability, it is expected that changes in abundance and biomass can result from shifts in the distribution of individual masses. We test these predictions using long-term data from a desert rodent community. Total energy use for the community has not changed directionally for 25 years, but species composition has. As a result, the average body size has decreased by almost 50%, and average abundance has doubled. These results lend support to the idea of resource limitation on desert rodent communities and demonstrate that systems are able to maintain community energy flux in the face of environmental change, through changes in composition and structure.     

Predictability in community dynamics

The coupling between community composition and climate change spans a gradient from no lags to strong lags. The no‐lag hypothesis is the foundation of many ecophysiological models, correlative species distribution modelling and climate reconstruction approaches. Simple lag hypotheses have become prominent in disequilibrium ecology, proposing that communities track climate change following a fixed function or with a time delay. However, more complex dynamics are possible and may lead to memory effects and alternate unstable states. We develop graphical and analytic methods for assessing these scenarios and show that these dynamics can appear in even simple models. The overall implications are that (1) complex community dynamics may be common and (2) detailed knowledge of past climate change and community states will often be necessary yet sometimes insufficient to make predictions of a community's future state.     

Evaluation of subsampling efforts in estimating community indices and community structures

Even though subsampling can minimize the research efforts needed to deal with numerous specimens, the accuracy of bioassessment and community analysis can be affected according to subsampled individuals. In this study, the effects of subsampling on community indices, the parameters of the species abundance distributions (SADs) and ordination based on communities were evaluated using benthic macroinvertebrates from three different stream pollution levels: less, intermediately, and heavily polluted. The values of the community indices and the parameters of the SADs were clearly different according to the differences in the pollution levels, regardless of subsampling efforts. Detrended correspondence analysis was applied to characterize similarities between the subsamples with different individuals based on community indices and the parameters of the SADs. A self-organizing map was used to characterize the community similarities and properties of the subsamples, differentiating the subsamples from their original datasets. Finally, our results revealed that the effects of subsampling were reflected differently in different indices, parameters, and ordinations of communities at different pollution levels, suggesting that subsample size should be determined differently at different pollution levels depending on the objectives of the study. However, if only one subsample size is to be used for simplicity and to reduce the cost of aquatic ecosystem health monitoring and assessment, then we recommend at least 400 individuals as the subsample size. At least 800 individuals should be subsampled for biodiversity studies.     

Phenotypic variation in nurse traits and community feedbacks define an alpine community

Much is known about facilitation, but virtually nothing about the underlying genetic and evolutionary consequences of this important interaction. We assessed the potential of phenotypic differences in facilitative effects of a foundation species to determine the composition of an Alpine community in Arizona. Two phenotypes of Geum rossii occur along a gradient of disturbance, with 'tight' competitive cushions in stable conditions and 'loose' facilitative cushions in disturbed conditions. A common-garden study suggested that field-based traits may have a genetic basis. Field experiments showed that the reproductive fitness of G. rossii cushions decreased with increasing facilitation. Finally, using a dual-lattice model we showed that including the cost and benefit of facilitation may contribute to the co-occurrence of genotypes with contrasting facilitative effects. Our results indicate that changes in community composition due to phenotypic differences in facilitative effects of a foundation species may in turn affect selective pressures on the foundation species.     

Bioinformatics in the community college

Biotechnology is becoming an information-based field. In this article we describe some resources available to instructors, show how these resources are used in the biotechnology training program, and provide examples of activities used by non-science majors to increase their understanding of biology. We discuss some of the challenges we have encountered using these tools in the classroom. Journal of Industrial Microbiology & Biotechnology (2000) 24, 314–318. Received 08 April 1999/ Accepted in revised form 10 November 1999     

Neutral theory in community ecology

One of the central goals of community ecology is to understand the forces that maintain species diversity within communities. The traditional niche-assembly theory asserts that species live together in a community only when they differ from one another in resource uses. But this theory has some difficulties in explaining the diversity often observed in specie-rich communities such as tropical forests. As an alternative to the niche theory, Hubbell and other ecologists introduced a neutral model. Hubbell argues that the number of species in a community is controlled by species extinction and immigration or speciation of new species. Assuming that all individuals of all species in a trophically similar com-munity are ecologically equivalent, Hubbell's neutral theory predicts two important statistical distributions. One is the asymptotic log-series distribution for the metacommunities under point mutation speciation, and the other is the zero-sum multinomial distribution for both local communities under dispersal limitation and metacommunities under random fission speciation. Unlike the niche-assembly theory, the neutral theory takes similarity in species and individuals as a starting point for investigating species diversity. Based on the fundamental processes of birth, death, dispersal and spe-ciation, the neutral theory provided the first mechanistic explanation of species abundance distribution commonly observed in natural communities. Since the publication of the neutral theory, there has been much discussion about it, pro and con. In this paper, we summarize recent progress in the assumption, prediction and speciation mode of the neutral theory, including progress in the theory itself, tests about the assumption of the theory, prediction and speciation mode at the metacommunity level. We also suggest that the most important task in the future is to bridge the niche-assembly theory and the neutral theory, and to add species differences to the neutral theory and more stochasticity to the niche theory.     

Neutral theory in community ecology

One of the central goals of community ecology is to understand the forces that maintain species diversity within communities. The traditional niche-assembly theory asserts that species live together in a community only when they differ from one another in resource uses. But this theory has some difficulties in explaining the diversity often observed in specie-rich communities such as tropical forests. As an alternative to the niche theory, Hubbell and other ecologists introduced a neutral model. Hubbell argues that the number of species in a community is controlled by species extinction and immigration or speciation of new species. Assuming that all individuals of all species in a trophically similar community are ecologically equivalent, Hubbell’s neutral theory predicts two important statistical distributions. One is the asymptotic log-series distribution for the metacommunities under point mutation speciation, and the other is the zero-sum multinomial distribution for both local communities under dispersal limitation and metacommunities under random fission speciation. Unlike the niche-assembly theory, the neutral theory takes similarity in species and individuals as a starting point for investigating species diversity. Based on the fundamental processes of birth, death, dispersal and speciation, the neutral theory provided the first mechanistic explanation of species abundance distribution commonly observed in natural communities. Since the publication of the neutral theory, there has been much discussion about it, pro and con. In this paper, we summarize recent progress in the assumption, prediction and speciation mode of the neutral theory, including progress in the theory itself, tests about the assumption of the theory, prediction and speciation mode at the metacommunity level. We also suggest that the most important task in the future is to bridge the niche-assembly theory and the neutral theory, and to add species differences to the neutral theory and more stochasticity to the niche theory. __________ Translated from Journal of Plant Ecology, 2006, 30(5): 868–877 [译自:植物生态学报]     

西双版纳的四籽柳群落

四籽柳群落是西双版纳山地沟谷常绿阔叶林的一种特殊类型,该群落结构简单,分层明显,林相相对整齐,虽有落叶现象,但季相变化不明显。上层树种以四籽柳占优势,形成单优势的四籽柳群落;幼灌层种类较少,不发达;草本层种类较多,但无明显优势种类;无大型木质藤本;大型附生植物不发达,但树干上有较多的苔藓附生植物。该群落是在云南南部山区特定的气候、特殊的立地、加上充分的水湿条件及适宜的土壤下发育形成的一种单优势的群落类型。该群落虽然有一定的四籽柳的预备种群,但缺乏更新苗,它是一种相对稳定并具有一定次生性的群落类型。     

Nitrogen uptake in the infiltration community, an ice algal community in Antarctic pack-ice

An infiltration community was the dominating ice algal community in pack-ice off Queen Maud Land, Southern Ocean, in January 1993. The community was dominated by autotrophic processes, and the most common species were the prymnesiophyte Phaeocystis antarctica and the diatoms Chaetoceros neglectus and Fragilariopsis cylindrus. The concentration of chlorophyll a was 1.3–47.9 μg l⁻¹, and the inner part of the community was nitrate depleted. Uptake rates of nitrate, nitrite, ammonium, urea and amino acids were measured using ¹⁵N. Nitrate was the major nitrogen source for ice algal growth (67 ± 6% nitrate uptake). It is suggested that % nitrate uptake in the infiltration community decreases during the growth season, from 92% during spring (literature data) to 67% during summer. Scalar irradiance in the infiltration community was high and variable. It reached ca. 2000 μmol m⁻² s⁻¹ at some locations, and nitrate uptake rate was potentially photoinhibited at irradiances >500 μmol m⁻² s⁻¹. Nitrate uptake rate in an average infiltration community (0.6 m of snow cover) was lowered by 13% over a 2-week period due to photoinhibition. Received: 16 December 1996 / Accepted: 5 January 1998     

Scoliosis in the community.

Screening for scoliosis at schools has become more and more popular despite the lack of knowledge concerning the clinical course of idiopathic scoliosis. An epidemiological study of 5303 schoolchildren showed three types of scoliosis in the community: (1) pelvic tilt scoliosis (an inconsequential deformity caused by an inequality in the length of the legs but accounting for almost 40% of curves detected); (2) spinal scoliosis (a minor asymmetry of the spine in the coronal plane that tends to remain static or to resolve and which may be normal in growing children, accounting for the remaining 60%); and (3) progressive scoliosis (10% of the spinal scolioses measuring 10 degrees or more that progress by 5 degrees or more a year). Progressive scoliosis resembles idiopathic scoliosis because in girls with right thoracic curves the potential for progression is appreciable. Until the natural history is better established growing awareness in the community of spinal deformity should help earlier detection, and screening should be directed towards providing subjects for further epidemiological work.     

Equity in community care.

The implementation of the NHS and Community Care Act 1990 made local authority social services departments responsible for the organisation and funding of support and care in the community. This development took effect at the same time as a blurring of the boundaries between health and social care. One consequence is that the relevance of equity (a guiding principle of the 1946 National Health Service Act, but relatively lacking from the 1948 National Assistance Act, the foundation of many social services) has come to be more keenly appreciated within personal social services. Equity questions arise in community care over the distribution of public resources between different client groups, income groups, generations, and localities. Moreover, no mechanisms exist to monitor the trends that emerge from different ways that people get access to care. Yet there is a risk that substantial divisive consequences may occur, particularly between generations.