Abstract
Anthropogenic changes in climate, land use, and disturbance regimes, as well as introductions of non-native species can lead to the transformation of many ecosystems. The resulting novel ecosystems are usually characterized by species assemblages that have not occurred previously in a given area. Quantifying the ecological novelty of communities (i.e., biotic novelty) would enhance the understanding of environmental change. However, quantification remains challenging since current novelty metrics, such as the number and/or proportion of non-native species in a community, fall short of considering both functional and evolutionary aspects of biotic novelty. Here, we propose the Biotic Novelty Index (BNI), an intuitive and flexible multidimensional measure that combines (a) functional differences between native and non-native introduced species with (b) temporal dynamics of species introductions. We show that the BNI is an additive partition of Rao's quadratic entropy, capturing the novel interaction component of the community's functional diversity. Simulations show that the index varies predictably with the relative amount of functional novelty added by recently arrived species, and they illustrate the need to provide an additional standardized version of the index. We present a detailed R code and two applications of the BNI by (a) measuring changes of biotic novelty of dry grassland plant communities along an urbanization gradient in a metropolitan region and (b) determining the biotic novelty of plant species assemblages at a national scale. The results illustrate the applicability of the index across scales and its flexibility in the use of data of different quality. Both case studies revealed strong connections between biotic novelty and increasing urbanization, a measure of abiotic novelty. We conclude that the BNI framework may help building a basis for better understanding the ecological and evolutionary consequences of global change.
Highlights
We argue that a species that is functionally dissimilar from the resident species
We demonstrate in this paper that the Biotic Novelty Index (BNI) framework is a helpful tool whenever the assessment of novel species assemblages or communities is needed, which may be useful in invasion ecology and in global change ecology, restoration ecology, or urban ecology
This study introduced the BNI and demonstrated its applicability as a framework to measure the ecological novelty of communities and species assemblages
Summary
Ecological novelty has received growing attention in the recent literature (e.g., Heger et al, 2019; Hobbs et al, 2006) focusing on novel organisms (Jeschke, Keesing, & Ostfeld, 2013), novel species interactions (Carthey & Banks, 2014; Pearse & Altermatt, 2013), novel communities (Lurgi, López, & Montoya, 2012), or novel ecosystems (Higgs, 2017; Hobbs, Higgs, & Hall, 2013; Hobbs, Higgs, & Harris, 2009). Heger et al (2019) recently broadened this definition, by proposing to use ecological novelty as an umbrella term for addressing consequences of global change for organisms, communities, ecosystems, and landscapes, which can be approached from multiple perspectives. A site can be novel in terms of abiotic conditions, resulting, for example, from changes in climate, nitrogen deposition, or pollution by microplastics. Novelty can result from changes in species composition, structure, or ecological processes generating biotic novelty (Heger et al, 2019). Rigorously measuring novelty requires explicit definition of the relevant variables (Radeloff et al, 2015)
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