Introduction

In polyspecific associations, groups of more than one species stay close, communicate, and coordinate activities together over a prolonged period. Biologists have observed such interspecific coordination of activities in a variety of fish, reptiles, birds, and mammals (Terborgh, 1990; Au, 1991; Ohtsuka et al., 1995; Stensland et al., 2003; Lee et al., 2005). One might predict that the potential for increased resource competition results in few polyspecific associations among closely related species. Primatologists have observed many of these associations among closely related anthropoid species (e.g., Gautier and Gautier-Hion, 1969; Waser, 1980; Struhsaker, 1981; Terborgh, 1983; Yoneda, 1984; Garber, 1988; Cords, 1990; Norconk, 1990; Oates and Whitesides, 1990; Podolsky, 1990; Burton and Chan, 1996; Holenweg et al., 1996; Leonard and Bennett, 1996; Nickle and Heymann, 1996). As in the nonprimate literature, the purported benefits of these primate associations include: more efficient feeding, foraging, and insect predation; better predator protection, detection, and vigilance; and enhanced social and mating opportunities (Gautier-Hion et al., 1983, 1997; Mitani, 1991; Buchanan-Smith,

Benjamin Z. Freed • Department of Anthropology, Emory University, Atlanta, GA 30322

1990, 1999; Manohar and Mathur, 1992; Peres, 1992; Honer et al., 1997; Noe and Bshary, 1997; Wachter et al., 1997; Chapman and Chapman, 2000; McGraw and Bshary, 2001; Bicca-Marques and Garber, 2003; Korstjens and Noe, 2004). One species may gain the benefit of having more eyes and more ears against predators without any increase in food competition that might otherwise occur with larger groups of the same species (Eckardt and Zuberbuhler, 2004). In other cases, primates may parasitize or confer little benefit to their associates (Porter, 2001). Finally, primate associations may simply result from chance occurrences (Waser, 1982, 1984; Buchanan-Smith et al., 2000).

Yet polyspecific associations have not been readily observed in most daylight-active prosimian communities. Typically when closely related species of lemurs share a habitat, they rarely coordinate their activities. In Antserananomby ring-tailed lemurs (Lemur catta) and rufous lemurs (Eulemur fulvus rufus) rarely meet (Sussman, 1972). In Ranomafana rufous lemurs displace red-bellied lemurs (Eulemur rubriventer), ruffed lemurs (Varecia variegata) chase rufous lemurs, and diademed sifakas (Propithecus diadema) rarely meet lemurs (Overdorff, Balko, and Hemingway, personal communication). In Beza Mahafaly sifakas (Propithecus verreauxi) and smaller troops of ring-tailed lemurs form polyspecific associations that may be an antipredator strategy during important reproductive periods (Sauther, 2002). Indri (Lndri indri) and diademed sifakas in Mantadia meet every 2 or 3 days; they feed together, but never travel, forage, or rest with one another (Powzyk, 1997). In northern Madagascar, only Arbelot-Tracqui (1983) and Wilson et al., (1989) have found a pair of sympatric, congeneric lemurs that seemed to tolerate one another readily, crowned lemurs (Eulemur coronatus) and Sanford's lemurs (Eulemurfulvussanfordi). By 1989, many of the details as to the frequency and context under which associations potentially formed were still unstudied.

In 1989 I began an etho-ecological study of co-occurrence among crowned lemurs and Sanford's lemurs (Freed, 1996). The primary focus of this study was to understand how these two morphologically similar, congeneric species shared the same habitat. Although both species shared highly overlapping home ranges, significant year-round and seasonal differences occurred in habitat use. Crowned lemurs selected understory resources, ranged farther, lived in slightly larger groups, and formed foraging subgroups to disperse themselves within their home range. Sanford's lemurs selected more middle story resources, ranged less, and lived in slightly smaller, more spatially cohesive groups. During seasons when resources (especially fruit from Leea spinea) were superabundant, both species tolerated each other, and generally consumed these widely available resources in somewhat different proportions. When resources became less available, both species foraged more often. It was during this season that both species sought each other, and associated regularly.

The purpose of this article is to examine why crowned lemurs and Sanford's lemurs readily interact and form polyspecific associations in northern Madagascar. Results are from two studies I conducted: a quantitative behavioral study from

1989 to 1991 in Mt. d'Ambre National Park (Freed, 1996); and 2004 surveys of both species west of Mt. d'Ambre and north in the Cap d'Ambre. I address to what extent both species associate with one another; the context under which both species associate; activity, foraging, and feeding preferences within associations; and whether associations of these species are limited to Mt. d'Ambre. Finally, I discuss the benefits of association between these species.

MATERIALS AND METHODS Study Sites

Quantitative behavioral data were collected at Ampamelonabe, along the western edge of the protected forest of Mt. d'Ambre National Park (12°32' 3.2''S latitude., 49° 7'55'' E longitude., elevation 875 m) (Figure 1). The site includes 83 hectares of humid forest near the origin of the Antserasera, Bevoay, and Sandrampiana rivers. Local people use a footpath through the site to transport produce between the nearby western savannah and Joffre-Ville, a farming town on the eastern edge of Mt. d'Ambre. Disturbance at the site is largely limited to this path; people have used it daily for over 60 years. Neither hunting nor logging has occurred at the site. The site receives 1959 mm of rain annually. The wet season occurs December through April, during which rain falls nearly every day (83% of the annual rainfall), temperatures are warm, and the wind is calm (except for tropical storms). It is during this season when the food species responsible for nearly 25% of both lemurs' diets, Leea spinea, bears no fruit. Dry season, the coolest season (low 14.4°C), occurs May through August. A trace of rain falls on one-third of the days. The season is typified by daily strong 80 km/hr seasonal winds known as the varatraza. Hot season, September through November, is the warmest season (high 29.4°C), receives 14% of the annual rainfall, and lacks the varatraza. The common fruit, Leea spinea, is readily available during the dry season and hot season.

Ampamelonabe is mostly evergreen, humid forest with five distinct strata. The forest floor includes herbaceous growth, dominated by Piper umbellatum. An understory below 9 m contained bushes (Lantana camara and Solanum indi-cum), saplings, and treelets (e.g., Malleastrum sp., Erythroxylum ferrugineum, Tarenna sp., and Bakerella sp.). A middle story occurs from 9 to 17 m, and is dominated by Leea spinea and Chrysophyllum boivinianum, for which the site is named locally. The canopy (17-25 m) is mostly continuous, and includes Cryptocarya sp., Chrysophyllum sp., and HHarungana madagascariensis. An emergent layer above the canopy is also present, and typically includes trees such as Canarium madagascariensis.

The only daylight-active primates are the study species. Nocturnal primates include Microcebus rufus, Cheirogaleus major, Phaner furcifer, Lepilemur septentri-onalis, and Daubentonia madagascariensis. Potential predators include mammals

Cap d' Ambre

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