Short Note Associations between species can influence the goodness of fit of species distribution models: The case of two passerine birds Federico Morelli a, *, Piotr Tryjanowski b a DiSTeVA, University of Urbino, Scientific Campus, 61029 Urbino, Italy b Institute of Zoology, Poznan University of Life Sciences, Wojska Polskiego 71C, 60-625 Poznan ´, Poland 1. Introduction Models are increasingly being used as key components of wildlife management programs because they provide a method to predict the outcomes of management and conservation strategies (Guisan et al., 2013). Species distribution models (SDMs) are numerical tools that combine observations of species occurrence or abundance with environmental estimates. These models can be used to provide understanding and/or to predict the species’ distribution across a gradient of landscape (Elith and Leathwick, 2009). Predictive species distribution models are commonly applied as tools for the purposes of conservation planning and management of ecosystems (Guisan and Zimmermann, 2000). Furthermore, the outputs of species distribution models (spatial explicit predictions of environmental suitability for species) are considered important tools for making robust conservation decisions and to provide predictions on environmental suitability (Guisan et al., 2013). Such models rely on the concept of the ecological niche being occupied by the detected species. However, there are several aspects that can affect the goodness of fit or performance of the species distribution models (Allouche et al., 2008; Guisan et al., 2007). The observed patterns in the spread of populations in nature are a result of the complex interplay between stochastic and deterministic factors, mainly environmental or/and demographic, as well as deterministic inter-species components (for example a predator–prey system) (Morozova et al., 2008). Environmental parameters (land-use typologies, climate variables, vegetation or landscape metrics) are often covariates (predictors) used as regressors into a model, but species traits may reflect differential responses to the processes that control their distribution and this can compromise the performance of models. Some examples are the use of biological traits (Seoane et al., 2005; Carrascal et al., 2006), but eco-ethological characteristics of the species can also have an impact. For example, is known that many Passeriformes birds usually avoid areas surrounding raptor nests (Meese and Fuller, 1989; Norrdahl and Korpima ¨ki, 1998; Suhonen et al., 1994). In contrast, species such as woodpigeons Columba palumbus nest close to bolder, more aggressive birds, such as the eurasian hobby Falco subbuteo, which provide protection against nest predators (Bogliani et al., 1999). The presence of raven Corvus corax has been Ecological Complexity xxx (2014) xxx–xxx * Corresponding author. Tel.: +39 3282097285.. E-mail addresses: federico.morelli@uniurb.it, morellius@libero.it (F. Morelli), piotr.tryjanowski@gmail.com (P. Tryjanowski). A R T I C L E I N F O Article history: Received 22 August 2013 Received in revised form 23 December 2013 Accepted 2 January 2014 Available online xxx Keywords: Species-associations SDMs Goodness of fit Shrikes Buntings Species-specific model A B S T R A C T Species distribution models (SDMs) are numerical tools that combine observations of species presence or abundance with environmental data, in order to develop predictive estimates about species distribution. The main variables used as regressors on SDMs are environmental parameters (climate variables, land- uses typologies, landscape metrics, etc.). However, there are several aspects that can affect the goodness of fit of species distribution models. For example, species traits, presence of associated species and anti- predator behaviors may cause differential responses to the processes that control their distribution. Considering these kinds of factors should improve the performance of models. In this work, SDMs were performed for two bird species found associated during initial exploration of data, by mean of a correlation matrix among bird occurrence. Models were performed first on environmental variables and then on environmental variables plus the occurrence of associated species. The goodness of fit of SDMs was compared using the area under the curve (AUC) and the likelihood ratio test. Our results showed how the associations between bird species can affect the goodness of fit of species distribution models. Specifically, we documented a significant increase in the AUC of the best model for red-backed shrike when adding the occurrence of corn bunting as a predictor. Our findings suggest how species-specific models in applied ecology can be developed to improve the predictive power of SDMs. ß 2014 Elsevier B.V. All rights reserved. G Model ECOCOM-430; No. of Pages 5 Please cite this article in press as: Morelli, F., Tryjanowski, P., Associations between species can influence the goodness of fit of species distribution models: The case of two passerine birds. Ecol. Complex. (2014), http://dx.doi.org/10.1016/j.ecocom.2014.01.002 Contents lists available at ScienceDirect Ecological Complexity jo ur n al ho mep ag e: www .elsevier .c om /lo cate/ec o co m 1476-945X/$ – see front matter ß 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecocom.2014.01.002