Alberto Jiménez-Valverde

Use of niche models in invasive species risk assessments

Risk maps summarizing landscape suitability of novel areas for invading species can be valuable tools for preventing species’ invasions or controlling their spread, but methods employed for development of such maps remain variable and unstandardized. We discuss several considerations in development of such models, including types of distributional information that should be used, the nature of explanatory variables that should be incorporated, and caveats regarding model testing and evaluation. We highlight that, in the case of invasive species, such distributional predictions should aim to derive the best hypothesis of the potential distribution of the species by using (1) all distributional information available, including information from both the native range and other invaded regions; (2) predictors linked as directly as is feasible to the physiological requirements of the species; and (3) modelling procedures that carefully avoid overfitting to the training data. Finally, model testing and evaluation should focus on well-predicted presences, and less on efficient prediction of absences; a k-fold regional cross-validation test is discussed.

Accounting for uncertainty when mapping species distributions: The need for maps of ignorance

Accurate mapping of species distributions is a fundamental goal of modern biogeography, both for basic and applied purposes. This is commonly done by plotting known species occurrences, expert-drawn range maps or geographical estimations derived from species distribution models. However, all three kinds of maps are implicitly subject to uncertainty, due to the quality and bias of raw distributional data, the process of map building, and the dynamic nature of species distributions themselves. Here we review the main sources of uncertainty suggesting a code of good practices in order to minimize their effects. Specifically, we claim that uncertainty should be always explicitly taken into account and we propose the creation of maps of ignorance to provide information on where the mapped distributions are reliable and where they are uncertain.

A multiple-site similarity measure independent of richness

The Diserud–Ødegaard multiple-site similarity index makes use of data on species shared by two or more sites, but produces equal similarity values in two different circumstances: species loss and true species turnover. We developed a new multiple-site similarity measure, which is independent of richness and performs better than the Diserud–Ødegaard index under conditions of equal richness between sites, because it discriminates between situations in which shared species are distributed evenly among sites or concentrated in few pairs of sites. We conducted several simulations to assess the relative performance of both the indices. The use of the new measure is recommended, enabling the simultaneous analysis of turnover and richness gradients based on two independent measures.

Determinants of local spider (Araneidae and Thomisidae) species richness on a regional scale: climate and altitude vs. habitat structure

Abstract 1. The habitat heterogeneity hypothesis states that the more complex the habitat, the higher the species richness. The present study analyzes the effect of local factors on regional spider (Araneidae and Thomisidae) richness. The main objective is to disentangle the relative importance of habitat structure and other environmental variables.

Species Distribution Models Do Not Account for Abundance: The Case of Arthropods on Terceira Island

The objective of this study is to investigate whether presence/absence models can be used as surrogates of arthropod abundance, and eventually under which circumstances such surrogacy is guaranteed. Presence/absence data for 48 arthropod species from Terceira Island were modelled using artificial neural networks. Probabilities of occurrence were correlated with abundance data from a standardized arthropod survey programme. Although a tendency was found for vagile species to show relationships, only nine species showed significant positive correlations between probability of presence and abundance. Five of these were exotic spider species with high abundances and wide distributions in several human-modified habitats. The patchy distribution of pristine habitats, the capacity to reach them and the probable low dependence on limiting resources, other than food, enhance the relationship. A lack of significant correlations for the majority of the species may be due to historical events, inappropriate scale, demographic controls of density, or the incapacity of presence/absence models to account for environmental suitability. The difficulty to identify a priori the species for which the relationship will hold advises against the use of species distribution models as surrogates of arthropod abundance.

Challenging species distribution models : the case of Maculinea nausithous in the Iberian Peninsula

Maculinea nausithousis the most endangered Iberian butterfly, being included in the Bern and Habitat directives and in the Spanish Red Book for invertebrates. We map its potential distribution in the Iberian Peninsula, identifying potentially suitable areas where to focus future surveys. Using presence/absence data and a set of environmental variables, the distribution of M. nausithous was modelled using Generalized Additive Models. Model results were filtered using land cover data to identify the anthropogenic grasslands inhabited by the species. The model obtained indicates that some Iberian areas that currently do not support M. nausithous populations could be environmentally suitable for the species. The reasons for these absences are discussed. Indeed, field surveys identified possible sources of uncertainty at finer scale, highlighting that deficiencies in land use GIS data might constitute an important source of error, able to explain both commission and omission errors (i.e., over and underpredictions) of the model.

Climate and regional beta‐diversity gradients in spiders: dispersal capacity has nothing to say?

Abstract.  1. The importance of dispersal capacity in structuring beta‐diversity gradients has been pointed out in a number of recent studies, making geographical distance (GD) an important predictor of the composition of assemblages apart from environment. In this study, we analyse the relative importance of climate, habitat complexity and GD in four spider families with different dispersal tendencies in the centre of the Iberian Peninsula.

The “Alluvial Mesovoid Shallow Substratum”, a New Subterranean Habitat

In this paper we describe a new type of subterranean habitat associated with dry watercourses in the Eastern Iberian Peninsula, the “Alluvial Mesovoid Shallow Substratum” (alluvial MSS). Historical observations and data from field sampling specially designed to study MSS fauna in the streambeds of temporary watercourses support the description of this new habitat. To conduct the sampling, 16 subterranean sampling devices were placed in a region of Eastern Spain. The traps were operated for 12 months and temperature and relative humidity data were recorded to characterise the habitat. A large number of species was captured, many of which belonged to the arthropod group, with marked hygrophilous, geophilic, lucifugous and mesothermal habits. In addition, there was also a substantial number of species showing markedly ripicolous traits. The results confirm that the network of spaces which forms in alluvial deposits of temporary watercourses merits the category of habitat, and here we propose the name of “alluvial MSS”. The “alluvial MSS” may be covered or not by a layer of soil, is extremely damp, provides a buffer against above ground temperatures and is aphotic. In addition, compared to other types of MSS, it is a very unstable habitat. It is possible that the “alluvial MSS” may be found in other areas of the world with strongly seasonal climatic regimes, and could play an important role as a biogeographic corridor and as a refuge from climatic changes.

Environmental and geographical determinants of beta diversity of leaf beetles (Coleoptera: Chrysomelidae) in the Iberian Peninsula

Abstract 1. The effect and relative importance of both environmental and geographic factors on species turnover of Chrysomelidae assemblages in the Iberian Peninsula was explored.

Marshalling existing biodiversity data to evaluate biodiversity status and trends in planning exercises

A thorough understanding of biodiversity status and trends through time is necessary for decision-making at regional, national, and subnational levels. Information readily available in databases allows for development of scenarios of species distribution in relation to habitat changes. Existing species occurrence data are biased towards some taxonomic groups (especially vertebrates), and are more complete for Europe and North America than for the rest of the world. We outline a procedure for development of such biodiversity scenarios using available data on species distribution derived from primary biodiversity data and habitat conditions, and analytical software, which allows estimation of species’ distributions, and forecasting of likely effects of various agents of change on the distribution and status of the same species. Such approaches can translate into improved knowledge for countries regarding the 2010 Biodiversity Target of reducing significantly the rate of biodiversity loss—indeed, using methodologies such as those illustrated herein, many countries should be capable of analyzing trends of change for at least part of their biodiversity. Sources of errors that are present in primary biodiversity data and that can affect projections are discussed.