Why Be Diurnal? Or, Why Not Be Cathemeral?

Abstract

As a behavioural strategy, cathemerality is thought to confer considerable advantages by allowing animals to extend activity flexibly into either the diurnal or nocturnal phase in response to the prevailing ecological conditions. Factors such as temperature, access to food sources and minimising the risk of predation are all thought to be important in promoting cathemerality, although previous studies have produced inconsistent results. This paper adopts a different approach by first asking whether an obligate diurnal species, the chacma baboon (Papio hamadryas ursinus), exhibits seasonal variation in behavioural flexibility in response to annual cycles of day length. While short day lengths are an important constraint on the activity of the baboons at De Hoop Nature Reserve, South Africa, long summer days permit considerable flexibility in thermoregulatory response, diet selection and patterns of habitat choice. Given that baboons adapt flexibly in response to a relaxation of time constraints, the question thus arises as to why diurnal and nocturnal primates do not adopt cathemeral activity patterns when time is constrained? For baboons, the costs of predation appear to prohibit exploitation of the nocturnal phase and it is likely that such constraints are true of most primates. It thus follows that Madagascar’s predatory environment must in some way permit or select for a cathemeral lifestyle. The importance of the predation by fossa (Cryptoprocta ferox) on the evolution of cathemerality is discussed.

Biogeography of time partitioning in mammals

“…At resolutions finer than the broad-scale patterns identified by this study, other factors are likely to play a role in structuring temporal partitioning strategies. These include habitat structure (8,38), interspecific or intraspecific competition (9, 10, 44), human disturbance, and predation pressure (4,45,46).…”

“…The rotation of the Earth partitions time into regular cycles of day and night, and although all points on the Earth's surface receive roughly equal durations of light and darkness over the course of a year, at mid to high latitudes seasonal variation in day length imposes an uneven distribution throughout the annual cycle. During the hours when the sun is below the horizon, there is seasonal and latitudinal variation in the duration of "biologically useful semidarkness" in the form of twilight and moonlight (1), modified by both the lunar cycle and variable cloud cover, providing changing opportunities for animals able to use visual cues for key behaviors including foraging, predator avoidance, and reproduction (2)(3)(4)(5)(6). Activity during both daylight and semidarkness may be further constrained by covariance between the natural cycles of light and temperature; the metabolic costs of thermoregulation place constraints on the time available for activity (7).…”

Predation and Cathemerality

“…There are two scenarios by which the derived activity pattern of the fossa could have evolved; neither of these scenarios relies on the 'evolutionary disequilibrium' model, whereby cathemerality among extant lemur species is interpreted as a transitional activity pattern between nocturnality and diurnality arising from the recent extinction of the 'giant' lemurs [van Schaik andKappeler, 1993, 1996;cf. Heesy and Ross, 2001;Hill, 2006]. In the fi rst scenario, it is possible that a cathemeral activity cycle was an adaptive response by the fossa to the existing, ancestral cathemeral activity patterns of its lemurid prey, as the activities of predators refl ect those of their prey [Emmons, 1987;Zuberbuhler and Jenny, 2002;Curtis and Rasmussen, 2002].…”

“…In the second scenario, lemurid cathemerality may have arisen in response to fossa cathemerality [see also Hill, 2006]. Both male and female fossas are sparsely distributed [Hawkins et al, 2002], with male home ranges being up to twice as large as those of females; Hawkins [2003] estimated the population density of C .…”

“…But, when we consider the range of raptor species that prey on ceboids, it appears that avian predation is a greater threat to ceboids than is carnivoran predation. Indeed, the threat of raptor predation may be great enough to outweigh any benefi ts from cathemerality, except under certain conditions [Hill, 2006]. Thus, the cathemerality of Aotus (and perhaps Alouatta ), might better be linked to predation in terms of avoiding raptor predation.…”