Ecological tolerances and optima — real or imaginary?

Ecological Indicators, 2011

Species tolerances are frequently used in multi-metric ecological quality indices, and typically have the strongest responses to disturbances. Usually the tolerances of many species are based on expert judgment, with little support from empirical ecological or physiological data. This is particularly true for fish of Mediterranean-type rivers, in which there are many basin-endemic taxa with little information on basic life history traits. In addition, the apparent tolerance of native Mediterranean freshwater fish species to naturally harsh environments and their short-term resilience may mask responses to man-made pressures. Consequently, we evaluated different statistical techniques and procedures for quantifying Mediterranean lotic fish tolerances and compared expert judgment of species tolerances with empirically determined tolerance values. We used eight alternative approaches to compute fish tolerance values for the Mediterranean basins of SW Europe. Three types of approaches were used: (1) those based on the concept of niche breadth along an environment/pressure gradient (five models); (2) those based on deviations from expected values at disturbed sites as predicted by statistical models describing relationships between species and environmental variables (generalized linear modelling (GLM) and generalized additive modelling (GAM), two models); and (3) one model based on the relatively independent contributions of pressure variables to the data variation explained by statistical models. Tolerance estimates based on the used/available pressure gradient and the average general pressure value had the highest mean correlations with the expert judgment classification (mean r = 0.4) and with the other approaches (mean r of 0.48 and 0.46, respectively). The high degree of uncertainty in tolerance estimates should be accounted for when applying them in ecological assessments. Results also highlights the need for better designed research to separate effects of natural and disturbance gradients on species occurrences and densities.

developing a set of predictor variables that aid management. We conducted a state-wide survey to examine the species richness of gall wasps (Hymenoptera: Cynipidae) on six oak species dominant in the threatened scrub-oak vegetation in peninsular Florida. Eighty-eight cynipid species were recorded; 23 were new species to Florida (a 35% increase), including 17 species new to science and 6 species newly recorded in the state. The cynipid species represented 68% of cynipids of Florida, on only 24% of oak species sampled. This fauna represents a hotspot of richness, justifying conservation initiatives in scrub-oak habitat and throughout the state. We derived predictor variables from general ecological concepts: (1) the theory of island biogeography that insect species richness increases as host plant geographic area increases and as local abundance increases, (2) the plant-architecture hypothesis that insect species richness increases with increased plant size, and (3) phytochemical patterns in leaves, including nutrients and digestibility reducers predicting suitability for insect herbivores. Concepts 1 and 2, developed for large scales and species numbers, were tested at smaller scales relevant to much conservation research and management. A stepwise multiple regression including all predictor variables accounted for 99% of the variance in cynipid species richness with three variables: foliar hemicellulose concentration (81%), host geographic area (16%), and tree height (2%). The trends were negative, however, and opposite to those predicted by concepts 1 and 2. Ecological theory was not applicable to discovery of predictors of cynipid species richness on six oak species. Thus, we promote caution in applying ecological theory to a narrow set of species without specific testing of how patterns conform to theoretical predictions.

Ecography, 2004

Thuiller, W., Brotons, L., Araú jo, M. B. and Lavorel, S. 2004. Effects of restricting environmental range of data to project current and future species distributions.

Landscape Ecology, 2009

This thesis addresses the spatial distribution and dynamics of vascular plant species in modern agricultural landscapes in SE Norway. This is done by analysing several data sets for species composition and environmental factors; the most important are 2201 patch elements located in 16 1-km 2 squares in SE Norway; data from farm ponds; and two data sets from present and former semi-natural grasslands, respectively. Eventually, results are compared to a companion study in a more traditional agricultural landscape of W Norway. Spatial and temporal patterns in species richness and composition are analysed by habitat specificity measures, ordination analyses and generalised linear modelling. A semi-natural affiliation index is used to assess the affiliation of each patch's flora to long-term extensively managed semi-natural grasslands versus intensively used agricultural land and waste ground. This thesis also includes a theoretical evaluation of habitat specificity indices, which forms the basis for the empirical studies. The theoretical study provides arguments for use of gamma diversity contribution and core habitat specificity measures in parallel and the empirical studies show that the context used for quantifying habitat specificity strongly influences the results. High values for both measures were observed for woodland, pastures and road verges, whereas midfield islets, boundaries and ploughed land types were in general ranked low, in both modern and traditionally used landscapes. These findings were also supported by the semi-natural affiliation index. Semi-natural grassland species were scatteredly distributed throughout whole landscapes but peaked in woodlands in addition to semi-natural grasslands. Both information on past land-use derived from an old cadastral map in addition to results from the study of modern agricultural landscape patches characterised by the semi-natural species Scorzonera humilis, indicate that many semi-natural affiliated species persist long after management practices has come to an end, and that an extinction debt may be present in the flora of abandoned grassland patches. Floristic gradients of agricultural landscape patch types identified by ordination methods were related to regrowth succession (reflecting long-term management and landuse intensity) and nutrient status. On the other hand, farm pond ecosystems showed few patterns in species compositional change over time, even though a slight increase in the nutrient content of pond waters was observed. The results indicate that plant species List of papers This thesis is based on six papers which will be referred to by their corresponding Roman numerals (I-VI). The published papers I, II and VI are reprinted with kind permission of the publishers.

One of the most challenging aspects of quality indices has been to compile reliable measures of the species' sensitivity to various magnitudes and different kinds of ecosystem attributes. Occupancy modelling has become increasingly useful to ecologists because provides a flexible framework to estimate the habitat use as a function of site information. We modelled occupancy of oligochaete species from physicochemical variables of Pampean streams; and we described the change in occupancy along the gradient of each explanatory physicochemical variable. We proposed three phases (resistance, tolerance and extinction) to describe the sensitivity of the species in terms of occupancy. Seventeen of the 33 taxa of oligochaetes were enough abundant to be modeled. In eight species, we obtained a total of 11 different models including physicochemical covariates. Occupancy was explained by conductivity in four species, by dissolved oxygen in three species, and by nutrients in four species. The analysis of phases (resistance, tolerance and extinction) to describe the sensitivity of the species in terms of occupancy, offers a new methodology to understand how the species behave along a stressor gradient. Detailed descriptions of sensitivity of these local species, will helps ecologists to generate more accurate biotic indices.

Journal of Vegetation Science, 1995

Sensitivity analysis, the study of how ecological variables of interest respond to changes in external conditions, is a theoretically well-developed and widely applied approach in population ecology. Though the application of sensitivity analysis to predicting the response of species-rich communities to disturbances also has a long history, derivation of a mathematical framework for understanding the factors leading to robust coexistence has only been a recent undertaking. Here we suggest that this new development opens up a new perspective, providing advances ranging from the applied to the theoretical. First, it yields a framework to be applied in specific cases for assessing the extinction risk of community modules in the face of environmental change. Second, it can be used to determine trait combinations allowing for coexistence that is robust to environmental variation, and limits to diversity in the presence of environmental variation, for specific community types. Third, it offers general insights into the nature of communities that are robust to environmental variation. We apply recent community-level extensions of mathematical sensitivity analysis to example models for illustration. We discuss the advantages and limitations of the method, and some of the empirical questions the theoretical framework could help answer.

Integrated Assessment of Running Waters in Europe, 2004

The present study aims to investigate whether taxa with a small distribution range or taxa with low abundances indicate specific habitats or a high ecological quality and what the effect is if these taxa are excluded from ecological assessment. We compared autecological features between stream dwelling taxa with a mean abundance >5 individuals per sample and a mean abundance ≤5 individuals per sample as well as between taxa with a small distribution range and taxa with a large distribution range. The number of rare taxa (either with a small distribution range or with low abundances) in a sample was related to the ecological quality classes. To test the effect of exclusion of rare taxa we constructed 8 data sets all including 142 samples of Dutch lowland streams. From each data set we stepwise excluded taxa that had low abundances or taxa that were known to be restricted in their distribution range. With help of the AQEM assessment software we calculated the final ecological quality classes and the metrics that were included in the multimetric for the original data and the 8 selected data sets.

Journal of Vegetation Science

Questions: : Heinz Ellenberg classically defined "indicator" scores for species representing their typical positions along gradients of key environmental variables, and these have proven very useful for designating ecological distributions. We tested a key tenent of trait-based ecology, i.e., the ability to predict ecological preferences from species' traits. More specifically, can we predict Ellenberg indicator scores for soil nutrients, soil moisture and irradiance from four well-studied traits: leaf area, leaf dry matter content, specific leaf area and seed mass? Can we use such relationships to estimate Ellenberg scores for species never classified by Ellenberg? Location: Global Methods: Cumulative link models were developed to predict Ellenberg nutrients, irradiance and moisture values from Ln-transformed trait values using 922, 981 and 988 species respectively. We then independently tested these prediction equations using the trait values of 423 and 421 new species that occurred elsewere in Europe, North America and Morocco and whose habitat affinities we could classify from independent sources as 3-level ordinal ranks related to soil moisture and irradiance. The traits were specific leaf area, leaf dry matter content, leaf area and seed mass. Results: The four functional traits predicted the Ellenberg indicator scores of site fertility, light and moisture with average error rates of < 2 Ellenberg ranks out of 9. We then used the trait values of 423 and 421 species respectively that occurred (mostly) outside of Germany but whose habitat affinities we could classify as 3-level ordinal ranks related to soil moisture and irradiance. The predicted positions of the new species, given the equations derived from the Ellenberg indices, agreed well with their independent habitat classifications, although our equation for Ellenberg irrandiance levels performed poorly on the lower ranks. Shipley et al. 4 Conclusions: These prediction equations, and their eventual extensions, could be used to provide approximate descriptions of habitat affinities of large numbers of species worldwide.