Dry Season Intersexual Habitat Partitioning by Flap-Necked Chameleons (Chamaeleo dilepis) in Kenya

In a wooded grassland in central Kenya during the dry season, male and female Chamaeleo dilepis exhibited differences in perch plants, perch heights, general body coloration, and rates of movement. By the end of the rainy season, the first three of these differences were no longer evident. Defoliation of a large proportion of the shrubs and lack of water probably created a dry season resource shortage for this population of chameleons. Thus, this expansion of the total niche may be viewed as ameliorating intraspecific competition, and it may be permitted by the absence of congeners in the habitat. NICHE EXPANSION BY INTERSEXUAL RESOURCE PARTITIONING has been documented primarily in birds following the initial suggestion of Rand (1952). It has been interpreted as a mechanism which alleviates intersexual competition under conditions of resources limitation (e.g., Hogstad 1977) or as a means of maximizing resource utilization in the absence of heterospecific competitors (Selander 1968). Differential habitat occupancy by the sexes has been reported for lizards (Jenssen 1970; Rand 1962, 1967). Schoener (1967) speculated that for arboreal species it might facilitate the build-up of dense populations in structurally rich habitats. Among chameleons, seasonal intersexual prey partitioning was found for Chamaeleo pumilis by Burrage (1973), and sexual dichromatism has been reported for C. hohnelii (Bustard 1965), C. namaquensis (Robinson 1978), and C. dilepis (Brain 1961). In the latter three cases, we might expect intersexual color differences to serve the function of matching the background colors of different microhabitats, although other explanations are possible. In this paper we report on differential microhabitat distribution in a population of C. dilepis in Kenya during the dry season and relate this to environmentally imposed stresses faced by the population. STUDY AREA AND METHODS The study area was situated on the eastern slope of Lukeya Hill (1?33'S, 37?5'E, elev. 1837 m), in the Athi Plains 38 km southeast of Nairobi. The vegetation in the area can be characterized as wooded grassland (Greenway 1973), with low bushes (Grewia tembensis) and scattered trees, mainly thorned torchwood (Balanites glabra) with individual yellow barked gall-acacias (Acacia seyal) and glossy-leaved commiphora (Commiphora schemperi). Ground cover consisted mostly of red oat-grass (Themeda triandra) with scattered stands of drop-seed grass (Sporobolus fimbriatus). The area is grazed by both domestic and wild herbivores. The climate is characterized by two distinct wet seasons, November to January and late March to mid-May, with an average annual rainfall of 900 mm. The study was conducted during the dry season, between 4 February and 25 March 1981. The grasses were dry and brittle, and many shrubs were leafless; only Balanites retained a green color. No rain fell until the night of 17 March, when the long rains began. Two independent studies in the Athi Plains have shown that insect density increases markedly during the rainy season. Dingle and Khamala (1972) found that insect biomass increased almost fourfold between March and May, and Denlinger (1980) found that densities of flying insects in Nairobi National Park were positively correlated with rainfall. Thus, the study period was likely one of depressed food as well as water availability for Chamaeleo dilepis. Five gravid female and four adult, male chameleons were fitted with 27 mHz transmitters constructed to fit across the mid-dorsal ridge like a saddle. They were glued to the animals with epoxy at the level of the pectoral girdle. Lifespan of the transmitters was about two months, and they had a transmitting range of 40 m. The devices fell off when the animals molted, but they could be re'Received 14 September 1982, revised 31 March 1983, accepted 19 April 1983. BIOTROPICA 16(1): 69-72 1984 69 This content downloaded from 157.55.39.183 on Fri, 22 Apr 2016 06:52:42 UTC All use subject to http://about.jstor.org/terms TABLE 1. Perch plants and body color of Chamaeleo dilepis before and after the 1981 rainy season, FebruaryMarch data are frequencies offirst sightings of radiotagged animals, June data represent individual sleeping animals, Female Male Chi-square