Diel niche variation in mammals associated with expanded trait space

Abstract

Mammalian life shows huge diversity, but most groups remain nocturnal in their activity pattern. A key unresolved question is whether mammal species that have diversified into different diel niches occupy unique regions of functional trait space. For 5,104 extant mammals we show here that daytime-active species (cathemeral or diurnal) evolved trait combinations along different gradients from those of nocturnal and crepuscular species. Hypervolumes of five major functional traits (body mass, litter size, diet, foraging strata, habitat breadth) reveal that 30% of diurnal trait space is unique, compared to 55% of nocturnal trait space. Almost half of trait space (44%) of species with apparently obligate diel niches is shared with those that can switch, suggesting that more species than currently realised may be somewhat flexible in their activity patterns. Increasingly, conservation measures have focused on protecting functionally unique species; for mammals, protecting functional distinctiveness requires a focus across diel niches.

The dimensionality and structure of species trait spaces

“…We also lack a synthesis on the main factors shaping the different aspects of species trait spaces. The degree of organismal complexity, which is related to the diversity of cell types (Valentine et al, 1994), can indeed influence the complexity of species trait space following key functional innovation in multicellular clades (Cox et al, 2021; Knoll, 2011; Sosiak & Barden, 2021). The environment can also be crucial in determining the course of multicellular evolution and organismal complexity, with aggregative multicellularity evolving more frequently on land whereas clonal multicellularity is more frequent in water (Fisher et al, 2020).…”

“…Several studies suggested that, beyond the positive influence of species trait diversity on ecosystem functioning (Craven et al, 2018; Gross et al, 2017), these unique species can play key and irreplaceable functional roles (Le Bagousse‐Pinguet et al, 2021; Maire et al, 2018; O'Gorman et al, 2011; Pigot et al, 2016a). The filling of this trait space through evolutionary history, and more particularly the emergence of species with unique traits, has also motivated numerous studies investigating specialisation in clades or competition footprint across the tree of life (Cornwell et al, 2014; Cox et al, 2021; Jarzyna et al, 2020; Phillips et al, 2018; Ricklefs, 2010; Stubbs & Benton, 2016). Yet we still lack a flexible framework in which the number and composition of species clusters but also unique species are automatically detected regardless of the shape, the density in terms of species richness and the dimensionality of the trait space in which they are embedded.…”

Mammals adjust diel activity across gradients of urbanization

“…Resource selection functions have been a popular and valuable tool to measure the relationship between available resources and animal populations, and have been used intensely in wildlife management and conservation (Strickland and McDonald, 2006). However, very little work has been done to quantify temporal habitat selection specifically (Cox et al, 2021; Gaston, 2019). Here, we built upon Farris et al (Farris et al, 2015) and developed an analytical approach to quantify temporal resource selection across environmental gradients.…”

Passive Acoustic Monitoring and Automatic Detection of Diel Patterns and Acoustic Structure of Howler Monkey Roars

“…The fact that howler loud calls are rarely studied at night is not surprising because nighttime studies are, in general, underrepresented in ecological research [8,9]. For example, calls from birds and primates, two of the most studied animal taxa, are mostly studied during the day because it is easier to collect daytime data and because researchers often assume diurnal animals are not active at night, despite the lack of empirical support for this assumption [8][9][10][11][12][13][14]. Anthropoids, except the genus Aotus, are considered diurnal.…”

“…However, there are reports of several anthropoids, such as mantled howler monkeys (Alouatta palliata), black-and-gold howler monkeys (Alouatta caraya), red-tailed monkeys (Cercopithecus ascanius), chimpanzees (Pan troglodytes), Ugandan red colobus monkeys (Procolobus rufomitratus Diversity 2021, 13, 566 2 of 12 tephrosceles), and Guianan red howler monkeys (Alouatta macconnelli) showing nocturnal activity [5,10,[14][15][16]. Diurnal sample bias [8,9] may preclude appreciation that species thought to be strictly diurnal are active during the full diel cycle [11][12][13][14].…”