Abstract
In order to understand species’ sensitivity to habitat change, we must correctly determine if a species is associated with a habitat or not, and if it is associated, its degree of specialization for that habitat. However, definitions of species’ habitat association and specialization are often static, categorical classifications that coarsely define species as either habitat specialists or generalists and can fail to account for potential temporal or spatial differences in association or specialization. In contrast, quantitative metrics can provide a more nuanced assessment, defining species’ habitat associations and specialization along a continuous scale and accommodate for temporal or spatial variation, but these approaches are less widely used. Here we explore relative habitat use (RHU) as a metric for quantifying species’ association with and degree of specialization for different habitat types. RHU determines the extent of a species’ association with a given habitat by comparing its abundance in that habitat relative to its mean abundance across all other habitats. Using monitoring data for breeding birds across Europe from 1998 to 2017; we calculate RHU scores for 246 species for five habitat types and compared them to the literature-based classifications of their association with and specialization for each of these habitats. We also explored the temporal variation in species’ RHU scores for each habitat and assessed how this varied according to association and degree of specialization. In general, species’ RHU and literature-derived classifications were well aligned, as RHU scores for a given habitat increased in line with reported association and specialization. In addition, temporal variation in RHU scores were influenced by association and degree of specialization, with lower scores for those associated with, and those more specialized to, a given habitat. As a continuous metric, RHU allows a detailed assessment of species’ association with and degree of specialization for different habitats that can be tailored to specific temporal and/or spatial requirements. It has the potential to be a valuable tool for identifying indicator species and in supporting the design, implementation and monitoring of conservation management actions.
Highlights
There is growing recognition that continued biodiversity declines and loss of species through land-use change and habitat degradation are occurring in a non-random manner, with specialist species’ populations declining at faster rates compared to generalist species (Devictor et al, 2010)
Specialism itself is characterised in two dimensions specialist species are defined as those whose populations are restricted to a smaller range of habitats and/or use a small portion of the resources that are available in a habitat (Reid et al, 2005; Smart et al, 2006; Devictor et al, 2008)
Generalist species are defined as those that are capable of exploiting a range of habitats, and/or use a larger number of the available resources in a habitat (Morelli et al, 2019); here we focus on definitions of specialization that are based on the range of habitats a species uses rather than resource use within habitats
Summary
There is growing recognition that continued biodiversity declines and loss of species through land-use change and habitat degradation are occurring in a non-random manner, with specialist species’ populations declining at faster rates compared to generalist species (Devictor et al, 2010). Assessments of specialization are often categorical, with species grouped into those that are associated with or are not associated with a given habitat, and whether those that are associated are habitat specialists or generalists (Fridley et al, 2007; Devictor et al, 2008, 2010; Chazdon et al, 2011; Herrando et al, 2016; Morelli et al, 2019). Specialism itself is characterised in two dimensions specialist species are defined as those whose populations are restricted to a smaller range of habitats and/or use a small portion of the resources that are available in a habitat (Reid et al, 2005; Smart et al, 2006; Devictor et al, 2008). Categorical classifications that define a list of species as specialized to a given habitat fail to acknowledge that there is variation between species in their degree of specialization for that habitat, and that this may have an important ef fect on their population trends over time (Reif et al, 2008)
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