Search

Comments on the elements of ecology and evolution. Ecological stoichiometry as the study of the balance of energy and multiple chemical elements in ecological interactions; Expansion of the concept of ecological stoichiometry to other organism and other ecosystems; Applications and horizons for stoichiometric theory.

Species distributions often show an aggregated pattern, which can be due to a number of endo- and exogenous factors. While autologistic models have been used for modelling such data with statistical rigour, little emphasis has been put on disentangling potential causes of aggregation. In this paper we ask whether it is possible to infer sources of aggregation in species distributions from a single set of occurrence data by comparing the performance of various autologistic models. We create simulated data sets, which show similar occupancy patterns, but differ in the process that causes the aggregation. We model the distribution of these data with various autologistic models, and show how the relative performance of the models is sensitive to the factor causing aggregation in the data. This information can be used when modelling real species data, where causes of aggregation are typically unknown. To illustrate, we use our approach to assess the potential causes of aggregation in data of seven bird species with contrasting statistical patterns. Our findings have important implications for conservation, as understanding the mechanisms that drive population fluctuations in space and time is critical for the development of effective management actions for long-term conservation. [ABSTRACT FROM AUTHOR]

The species–time relationship (STR) describes how the species richness of a community increases with the time span over which the community is observed. This pattern has numerous implications for both theory and conservation in much the same way as the species–area relationship (SAR). However, the STR has received much less attention and to date only a handful of papers have been published on the pattern. Here we gather together 984 community time-series, representing 15 study areas and nine taxonomic groups, and evaluate their STRs in order to assess the generality of the STR, its consistency across ecosystems and taxonomic groups, its functional form, and its relationship to local species richness. In general, STRs were surprisingly similar across major taxonomic groups and ecosystem types. STRs tended to be well fit by both power and logarithmic functions, and power function exponents typically ranged between 0.2 and 0.4. Communities with high richness tended to have lower STR exponents, suggesting that factors increasing richness may simultaneously decrease turnover in ecological systems. Our results suggest that the STR is as fundamental an ecological pattern as the SAR, and raise questions about the general processes underlying this pattern. They also highlight the dynamic nature of most species assemblages, and the need to incorporate time scale in both basic and applied research on species richness patterns. [ABSTRACT FROM AUTHOR]

The relationship between above and belowground species composition has been researched in forests, grasslands, and wetlands to understand what mechanisms control community composition. I thoroughly reviewed 108 articles published between 1945 and 2006 that summarized and provided specific values on similarities between above and belowground communities to identify common trends among ecosystems. Using Sørenson's index of similarity, I found that standing vegetation and its associated seed bank was the least similar in forest ecosystems, most similar in grasslands, and of intermediate similarity in wetlands. I also discovered that species richness was not related to seed bank – vegetation similarity in any of the three ecosystems. Disturbances were a common mechanism driving community composition in all ecosystems, where similarity decreased with time since disturbance in forest and wetland ecosystems and increased with time since disturbance in grasslands. Knowing the relationships between seed bank and standing vegetation may help conservationists to manage against exotic species, plan for community responses to disturbances, restore diversity, and better understand the resilience of an ecosystem. [ABSTRACT FROM AUTHOR]

The article reports on the significance of individual foraging specialization towards ecology, conservation, and evolution. According to the author, there are various studies which identified as well as investigated individual foraging specialization; however, the results of said investigations failed to come with a common definition of specialization. The author further argues that there is a need to clearly identify characteristics of niches that feature information about individual foraging specialization in order to remedy the complexity brought about by the diverse approaches.

The article presents a discussion on alternative stable states (ASS) in ecology. It argues the theories of R. K. Didham and colleagues regarding ASS of ecological communities. It also cites the three major criteria for ASS such as it must be shown to occur in the same environment, the perturbation which causes the change in species composition must be applied as a pulse and must not cause a prolonged change in the environment, and it must be self sustaining. ASS has been discussed mainly for semi-arid rangelands.

Hubbell's neutral theory of biodiversity has generated much debate over the need for niches to explain biodiversity patterns. Discussion of the theory has focused on its neutrality assumption, i.e. the functional equivalence of species in competition and dispersal. Almost no attention has been paid to another critical aspect of the theory, the assumptions on the nature of the speciation process. In the standard version of the neutral theory each individual has a fixed probability to speciate. Hence, the speciation rate of a species is directly proportional to its abundance in the metacommunity. We argue that this assumption is not realistic for most speciation modes because speciation is an emergent property of complex processes at larger spatial and temporal scales and, consequently, speciation rate can either increase or decrease with abundance. Accordingly, the assumption that speciation rate is independent of abundance (each species has a fixed probability to speciate) is a more natural starting point in a neutral theory of biodiversity. Here we present a neutral model based on this assumption and we confront this new model to 20 large data sets of tree communities, expecting the new model to fit the data better than Hubbell's original model. We find, however, that the data sets are much better fitted by Hubbell's original model. This implies that species abundance data can discriminate between different modes of speciation, or, stated otherwise, that the mode of speciation has a large impact on the species abundance distribution. Our model analysis points out new ways to study how biodiversity patterns are shaped by the interplay between evolutionary processes (speciation, extinction) and ecological processes (competition, dispersal). [ABSTRACT FROM AUTHOR]

Despite the importance of community-structuring processes operating at both local and regional scales, there is relatively little work examining both forces within a single system. I used a combination of observational and experimental approaches to examine the processes structuring larval dragonfly distributions in lentic habitats that encompass a gradient of both permanence and top predator type. I compared the relative vulnerability of species to predators from different portions of this gradient to assess the role of predation as a local force structuring communities. I also assessed the role of regional processes on species’ distributions by examining species’ propensity to disperse to and colonize artificial ponds distributed across a landscape. In both studies I contrasted habitat specialist species, which had larvae restricted to permanent lakes, with habitat generalist species, which had larvae that occur broadly across the habitat permanence and top predator transition. Results from this work suggest that dispersal and colonization behavior were critical mechanisms restricting the distributions of habitat specialist species, but that predation may act to reinforce this pattern. The habitat specialists dispersed less frequently, colonized artificial ponds less often when they did reach them, and most moved shorter distances than the habitat generalist species. Habitat specialists were also more vulnerable than habitat generalists to an invertebrate top predator with which they do not co-exist. Results from these studies suggest that species distributions can be shaped by processes operating at both regional and local spatial scales. The role of dispersal and recruitment limitation may be generally underestimated as a force shaping species distributions and community structure across habitat gradients in which there is a transition in both the biotic interactions and the disturbance interval across that gradient. [ABSTRACT FROM AUTHOR]

We investigated if dragonfly larvae community composition and species abundance curves are sensitive to variation in predation intensity, and whether the fit to a particular niche partitioning model could be used to make inferences about mechanisms structuring communities. The approach taken was to compare communities in lakes either having or lacking fish predation. Dragonfly species classified as active, strongly dominated the dragonfly communities in fishless lakes, and low active species dominated fishless lakes. As activity level is known to correlate with susceptibility to fish predation this indicates that these communities are structured by fish predation. Fitting relative abundance data to five niche partitioning models showed that the same model fitted data from both types of habitats (fish/no fish). This means that the observed differences in relative abundances were substitutive, i.e. the relative abundance of a rank stayed constant, even though the identity of the species having this rank changed. The best fit to data from both types of lakes was found for the random assortment model, which is usually interpreted as an indication that the community is not structured by within-guild interactions. This interpretation for fishless lakes did not seem to agree with other community measures (i.e. lowered diversity and evenness and no relationship between species richness and dragonfly biomass), which indicate that the community is structured by within-guild interactions. Moreover, a detail in the fitting procedure, the number of species included in the analysis, affected which model that fitted data best. Thus, we question if fitting niche partitioning models to data can provide mechanistic understanding of how resources are partitioned in natural communities. [ABSTRACT FROM AUTHOR]

T. Fukami and W. G. Lee argue that the logical expectation from ecological theory is that competitively-structured assemblages will be more likely to exhibit alternative stable states than abiotically-structured assemblages. We suggest that there are several important misinterpretations in their arguments, and that the substance of their hypothesis has both a weak basis in ecological theory and is not supported by empirical evidence which shows that alternative stable states occur more frequently in natural systems subject to moderate- to harsh abiotic extremes. While this debate is founded in ecological theory, it has important applied implications for restoration management. Sound theoretical predictions about when to expect alternative stable states can only aid more effective restoration if theoretical expectations can be shown to translate into predictable empirical outcomes. If strongly abiotically- or disturbance-structured systems are more likely to exhibit catastrophic phase shifts in community structure that can be resilient to management efforts, then restoration ecologists will need to treat these systems differently in terms of the types of management inputs that are required. [ABSTRACT FROM AUTHOR]

Many ecological interactions that are called mutualistic are in fact mixtures of antagonistic and mutualistic aspects. For example, plasmids exploit their bacterial hosts but also protect them against external threats. In this study, we analyse the conditions for the evolution of what we call ‘dangerous liaisons’: interactions combining mutualistic and antagonistic aspects. Starting point of our analysis is a model that was proposed as early as 1934. In this model, partners have to form a complex (either temporary or long lasting) in order to interact. Using this model framework we then set out to define and tease apart private interests of the interacting partners from their common good. This dichotomy provides a unifying perspective to classify ecological interactions. We discuss some examples to illustrate how the outcome of the interaction may depend on densities or on other contextual variables. Finally, we note that having a common good is not a necessary condition for partners to have aligned interests. In a dangerous liaison partners may have interest to cooperate even when this does not bolster the common good. [ABSTRACT FROM AUTHOR]

As a potential mechanism to explain how biodiversity loss may influence variability in ecosystem functioning, we examine the hypothesis that biodiversity loss lowers similarity in species composition among local communities and that this decreased similarity in turn lowers ecosystem reliability. Ecosystem reliability refers to the probability that a system will provide a consistent level of performance over a given unit of time. This hypothesis is compared with other hypotheses that make similar predictions, including the sampling effect, insurance, and resource use complementarity hypotheses. We provide evidence for the similarity hypothesis through a reanalysis of a recent experiment and show that a key assumption of the hypothesis may be robust through computer simulations. We also address problems and possible solutions regarding how to separately test the similarity and other hypotheses in biodiversity experiments. [ABSTRACT FROM AUTHOR]

A cybernetic system can be defined as one controlled by feedback, that is, a system in which input is partially determined by output. I explored the cybernetic properties of a simple planktonic ecosystem by introducing an artificial feedback loop; light energy delivered to the system was linked to the ecosystem's productivity and respiration. Specifically, I programmed a computer to turn lights on and off when dissolved oxygen reached low and high setpoints, respectively. Three treatments were applied that differed in light intensity and in range between high and low setpoints. Experiments were repeated under high and low nutrient conditions. The added feedback did not substantially alter responses to limiting factors from those expected under fixed duration lighting. However, several novel features were observed, including poor coupling between productivity and respiration, similar patterns in energy demand among treatments, and oscillations in primary productivity. These observations can be viewed as support for a holistic, cybernetic view of ecological systems. This view complements the dominant mechanistic-reductionist perspective on causality in ecosystems. The experimental addition of new feedback is apparently a useful means of investigating the self-organizational properties of ecosystems and may also improve our understanding of the consequences of anthropogenically induced feedback in natural and managed systems. [ABSTRACT FROM AUTHOR]