Why do we need a functional diversity approach to assess environmental changes in animals? First, functional diversity is defined by morphological and biological traits that determine how species operate within an ecosystem and interact with other species, as well as their use of habitat (Violle et al., 2007; Cadotte et al., 2011). These traits reflect how species influence ecological processes (effect traits) or how species respond to environmental changes (response traits) (Violle et al., 2007; Suding et al., 2008; Devictor et al., 2010). For example, animals' feeding habits are directly linked to ecosystem services that provide (Cardinale et al., 2012) and so is their role in trophic cascades (Kagata & Ohgushi, 2006). Unfortunately, human activities can negatively impact trophic cascades, ultimately leading to changes in biological communities' functional diversity and ecosystem services, causing a shift in ecosystem properties (Thébault & Loreau, 2003; Hines et al., 2015; Allhoff & Drossel, 2016). Second, functional diversity can be highly precise in assessing how each species or community responds to environmental change. Part of the rationale is as follows. In communities dominated by species with unique traits, each species fulfils a biological function (Kagata & Ohgushi, 2006; Villéger et al., 2008; Brousseau et al., 2018; Auber et al., 2022). In contrast, communities with species sharing similar traits (redundant species) are more resilient to disturbances because the loss of one species does not mean the loss of a function (Flynn et al., 2009; Laliberté et al., 2010; Mayfield et al., 2010), with some exceptions in highly diverse communities (Mouillot et al., 2014). Moreover, functional redundancy is associated with spatial scale. Low environmental variability at small spatial and temporal scales favors functional redundancy, while at larger scales, environmental variation is greater, favoring the coexistence of more diverse species’ traits (Macintyre et al., 2018). Functional diversity at the macroecological scale (regional or national) determines effect traits for local communities and informs about the vulnerability of ecosystem functioning to biodiversity change at larger scales. However, we are still unable to inform about mitigation strategies to conserve the provision of ecosystem services given our current lack of understanding of such large-scale and long-term trends (Greenop et al., 2021).
Anthropogenic disturbances are powerful regulators of community structure and composition through species loss (Kagata & Ohgushi, 2006; Auber et al., 2022), with land-use change being one of the most important drivers (Murphy et al., 2020). With their rapid adaptation and short life cycles, insects show fast responses to land-use change, yet the response is taxon-specific (Birkhofer et al., 2015). While some communities are less resilient (Rocha-Ortega et al., 2017), others are more resilient (Gerisch et al., 2012; Micó et al., 2020). Regarding trophic levels, higher levels are more susceptible to disturbance (Murphy et al., 2020), and their response depends on the choice of their prey (Wimp et al., 2011). Insects are fundamental for ecosystem functioning (Haddaway et al., 2020). Therefore, it is necessary to study their community response to human disturbance using functional metrics (Didham et al., 2010), as they help to understand their resilience and relate the ecological role of their diversity to their relevance for ecosystem services (Schowalter et al., 2018; Dangles & Casas, 2019). This is particularly important for communities of predatory insects as they may be the most vulnerable to human disturbance (Murphy et al., 2020).
Dragonflies (suborder Anisoptera) and damselflies (suborder Zygoptera), collectively grouped in the order Odonata, are ideal for studying the variation in the functional response of predators in the face of human-driven environmental change. They are generalist predators that feed on a wide range of small-sized, winged prey (Gómez-Anaya et al., 2011; Stoks & Córdoba-Aguilar, 2012; González-Soriano & Novelo-Gutiérrez, 2014). Previous studies have shown that land-use change (LUC) over time has little effect on odonate species richness, but it significantly alters their communities' composition (Rocha-Ortega et al., 2019a). However, LUC filters certain traits, such as thorax size (Rocha-Ortega et al., 2019b). Dragonflies and damselflies are taxa with relatively low species richness compared to other insects yet they have a well-resolved taxonomic knowledge (Abbott et al., 2005). These suborders exhibit distinct morphological characteristics, behaviors, thermal tolerances, and extinction risks in North America (Rocha-Ortega et al., 2020). Assessing the impact of LUC overtime on the taxonomic and functional diversity of odonates could allow us to assess how environmental change affects insect predator function.
We address here the following questions: Has the functional diversity of odonates changed over time following LUC in Mexico? Do dragonflies and damselflies respond differently to LUC? Are odonates functionally redundant in the face of LUC in Mexico? Given the high species turnover observed (Rocha-Ortega et al. 2019a), we expect functional diversity will remain relatively stable across land uses. Regarding the second question, we anticipate differences in the response of each suborder to LUC due to their morphological distinctions (Stoks & Córdoba-Aguilar, 2012; Rocha-Ortega et al. 2019a,b). Finally, considering the minimal changes in species richness in the study area (Rocha-Ortega et al. 2019a) and all species belonging to the same feeding guild, we expect no relationship between functional and taxonomic diversity of odonates, thus exhibiting high functional redundancy and group resilience.