Introduction

The effects of hurricanes and the process of forest recovery have been well-studied in the Caribbean, especially in Puerto Rico (e.g., Sanford et al., 1991; Walker et al., 1991; Walker, 1995). However, long-term investigations of the effects of severe

Jonah Ratsimbazafy • Durrell Wildlife Conservation Trust - Madagascar Programme, 101 Antananarivo, Madagascar natural disaster upon forest recovery processes have received only limited study to date in most tropical rainforests. Behavioral strategies used by species or groups of species experiencing natural disasters are important with respect to their subsequent recovery in the particular forest affected. It can be extremely useful to determine how different species have responded to the cumulative impact of human activities and natural disturbances of their natural habitats (e.g., cyclone, flooding, windstorms, fires, or drought) in order to improve species management for conservation purposes. Primates are an excellent group of animals to study when attempting to understand the impact of habitat alterations on the fauna of a tropical forest (Struhsaker, 1997). They can be relatively easy to census, and individual species in a given community often respond differently to habitat disturbance (Lovejoy et al., 1986; Ganzhorn, 1994; Estrada and Coates-Estrada, 1996; Tutin et al., 1997). Indeed, primates respond in complex and varied ways to different types and levels of disturbance (Dunbar, 1988). Obviously, the effects of habitat disruption on a primate population depends upon the nature and extent of forest alteration, the time since such alteration took place, as well as the requirements and adaptability of each primate species inhabiting an area (Wilson and Wilson, 1975; Cowlishaw and Dunbar, 2000). Nevertheless, studies on primate communities show that some species are more adaptable and resistant than others in response to habitat disturbance (Cody, 1981; Ganzhorn et al., 1999).

It is also important to remember that dietary flexibility is an important feature of ecology of all primates, even though species can be characterized as favoring one type of diet (Cowlishaw and Dunbar, 2000), as dietary category of a particular species can vary from one habitat to another. For example, gorillas in Rwanda are typically terrestrial folivores, whereas those in Gabon are typically arboreal frugivores (Tutin et al., 1991).

Obtaining food of appropriate quality and quantity, and avoiding predators are often considered to be conflicting goals for animals living in the wild (van Schaik and van Hooff, 1985; Koivula et al., 1995). The difficulty of reconciling these conflicting goals may be aggravated when pristine forests become fragmented and/or altered. Currently, there is growing interest in learning how primates cope with extreme forest degradation and destruction (see Johns, 1986, 1991; Estrada and Coates-Estrada, 1996; Cowlishaw and Dunbar, 2000).

Empirical studies have demonstrated that the combined effects of natural catastrophe (e.g., cyclone or wind storm) and anthropogenic disturbance can cause levels of habitat destruction to increase spatially and temporally. Consequently, favored foods become less abundant, and different primate species must employ different behavioral strategies in response to environmental change. de Ruiter (1986) demonstrated that large groups of Cebus olivaceus may travel farther than small groups, and forage less on fruit, and large groups can compensate for loss of fruit by foraging more on invertebrates. Such behavior demonstrates the ability of C. olivaceus to feed opportunistically on available food resources. Research on Callithrix flaviceps indicates that this species can substitute gum for fruit as a source of carbohydrates during periods of food scarcity. This strategy enables C. flaviceps to survive in small patches of highly disturbed habitats (Ferrari and Diego, 1995).

The rainforest habitats of Madagascar constitute a good starting point for studying behavioral responses in lemurs, as habitat disturbance is not restricted to anthropogenic pressures. Indeed, natural disturbances are common, and are of great concern (Jolly, 1989; Richard and Connor, 1997; Wright, 1997). However, little has been written about the impact of natural disasters of this island, or the adaptive responses of lemurs to highly altered habitats. Therefore, in this study, I am interested in behavioral response strategies used by black-and-white ruffed lemurs (Varecia variegata) to the combined effects of human-induced pressures and natural disturbances. Long-term studies of ruffed lemurs have only been conducted in pristine, less disturbed forests and in captivity. It appears that V. variegata is susceptible to habitat disturbance to a far greater degree than are most other lemur taxa (White et al., 1995; Ratsimbazafy, 1999).

The ruffed lemur is one example of a group-living prosimian that exhibits great flexibility in grouping patterns (group size: 2-31) (Morland, 1991a,b; Rigamonti, 1993; Balko et al., 1995; Vasey, 1997; Balko, 1998; Ratsimbazafy, 2002a; Louis et al., 2005; Lehman et al., 2005). Ruffed lemurs are highly frugivorous (nearly 75% of their diet is fruits), but they can supplement fruits with varying amounts of other food resources (e.g., leaves, flowers, nectar) during times of food shortage (see Morland, 1991a; Rigamonti, 1993; White et al., 1995; Balko, 1998; Ratsimbazafy, 2002a,b; Ratsimbazafy et al., 2002; Mittermeier et al., 2006). V. variegata has been described as the most reproductively stressed of all primates because of its high maternal investment (Tilden, 1994). In other words, Varecia is an ideal candidate for this natural experiment (Ratsimbazafy and Ratsirahonana, 1998).

From June to July 1997 and from February 1999 to July 2000, research was conducted on the southernmost population of black-and-white ruffed lemurs, at Manombo forest, in southeastern Madagascar. Manombo is a good location to carry out investigations on lemur behavioral responses, as this environment combines human pressures with a history of stochastic windthrow damage from the annual cyclone season.

In this chapter, I discuss foraging and feeding behavior in relation to food availability used by Varecia v. editorium living in an abruptly disturbed habitat. In addition to collecting data on activities such as feeding, foraging, traveling, resting, and others (e.g., social and agonistic), I examined the relative use of different plant species by each individual during different seasons and throughout the study. In this way, I could document not only the proportions of fruits, leaves, nectar, and other items in the diet, but also individual preferences for certain plant species and families, and the role of alien plant species in the Varecia diet. My data were also compared with data on the same species collected in undisturbed habitats.

METHODS Study Site Description

The study was conducted in a southeastern lowland rainforest in Madagascar, the Manombo forest. Manombo forest is comprised of the Manombo Special Reserve (MSR) and the Manombo Classified forest (MCF). Manombo is located in the province of Fianarantsoa at 23° 02'S and 47° 44'E (Figure 1). The MSR and CFM cover 14,000 ha, but only 9000 ha remains forested (Ratsimbazafy, 2002a). The elevation of the forest ranges between sea level and 137 m.

The climate of Manombo is characterized by high rainfall throughout the year, with heaviest rainfall during the cyclone season, from January through March. During this period, the area is subject to cyclones from the Indian Ocean, causing flooding, stream-course changes, and extensive tree falls (Donque, 1975).

In January 1997, cyclone "Gretelle," with winds up to 245 km, hit Manombo forest for 12 hours causing extensive damage: uprooting trees, breaking trunks

Figure 1. Location of Manombo Forest study area in Madagascar. Madagascar map: forest cover after Green and Sussman (1990). Inset: GIS data courtesy of ANGAP (Laborde Projection)

and large branches, toppling the canopy trees, and defoliating most of the remaining canopy. Postcyclone botanical transect studies revealed 85% canopy loss. Three years after the cyclone, alien plant species have invaded more than 40% of the total forested area. Currently, seven species of plant invaders have become potential threats to the native vegetation, especially in forested areas already subject to anthropogenic disturbances. As such, Manombo forest provides a unique environment in which to study habitat disturbance.

Study Individuals

Following a 2-month habituation period, I continuously studied two groups of V variegata for a period of 18 months. Although the composition of each group did not change during the study, only one adult male that was present in Group I during a 3-month survey in 1997 survived to 1999. Group I comprised three members (one male, Redy-M, and two females, Boloa-F and Silvera-F), while neighboring Group II consisted of two members (a male, Grina-M, and a female, Kolara-F).

Individual scans on the study groups were taken 10 days each month for a total of 1431 hours of observations on 188 days (total scans =17,171). Data are unavailable on Grina-M for the months from April to June 1999, and in July 2000. In addition, Kolara-F was missing during the months of April and May 1999, and in July 2000. Boloa-F disappeared during June 1999 and again in April 2000. Comparisons between groups were not always possible (as each group has relatively few individuals in each age/sex class); therefore, comparisons were made between individuals in statistical analyses.

Behavioral Methods

Data collection procedures involved focal animal sampling (Altmann, 1974). With the help of field assistants, groups were followed for a full day's activities whenever possible. Each day, a different focal animal was chosen in order to obtain a representative sample among individuals and across sexes. Individual scans on the study groups were taken 10 days each month for a total of 1431 hours of observations on 188 days (total scans = 17,171).

The activity of a focal animal was recorded at 5-minute intervals during daylight hours ("instantaneous" samples, Altmann, 1974). Behaviors were described at a general level (forage, feed, travel, rest, other). Specific behaviors provided more detailed records of these general activity categories. Each of the activity states was scored as an activity record for the corresponding 5-minute interval. The percentages of time spent at each activity were then calculated in relation to the total activity records for each 5-minute interval (Milton, 1980).

Feeding activity was defined as: reaching for, picking, placing in the mouth, chewing, and swallowing food items, whereas foraging was defined as moving slowly with attention directed toward a food source or manipulating substrates in search of foods (Whitten, 1983; O'Brien and Kinnaird, 1997). As feeding data are based on scans, they are measures of the frequency in which the focal animal fed on each item every 5 minutes. The food item and the part eaten were categorized and described as ripe or unripe fruit (only the fleshy part and/or the seed or both), young or mature leaves, flower parts, or miscellaneous materials (e.g., sap, bark) (see Overdorff, 1993).

The availability of different food was estimated using Importance Values (IV) (Curtis and Mcintosh, 1951). The IV takes into account relative tree density, distribution (relative frequency), and relative dominance (basal area). The IV data were taken from a postcyclone survey of 665 trees. The IV are calculated by the equation

Importance value (IV, ) = RD + RF + RDo r ^ tree species i'

where

RD = (number of individuals of species i/total individuals of all species) x 100 RF = (number of species at which species i occurs/total number of points sampled) x 100

RDo = (total basal area of species i/total basal area of all species) x 100 [Basal area (cm2) = (dbh)2 x (0.7854)]

Rainfall and temperature (maximum and minimum) were recorded daily at the study site and the mean monthly values were calculated. Combining these two climate parameters resulted in a total of eight seasons. The following criteria were used to define seasons:

"Rainy": average monthly precipitation (AFM) > 400 mm; "Moist" if AFM 400 - 200 mm; and "Dry" if AFM < 200 mm.

"Hot": temperature (T) > 20°C; "Cool" if (T) 20-15°C; and "Cold" if (T) < 15°C.

RESULTS Dietary Patterns

Overall: Combining data from five individuals, black-and-white ruffed lemurs were observed to feed on a total of 83 different plant species during the dry and rainy seasons combined (see Table 1). This is about 12% of the total number of species recorded in my seven sample transects. Among the species eaten, 70 were used as fruit sources, 17 as leaf sources, 2 as nectar sources, and 4 as other item sources. Thus, the number of species used as fruit sources is more than four times the number of leaf species and more than 11 times the number of nectar and other items together. As Table 1 shows, only 1% of those 82 species was used for food sources in all three categories (fruit, leaf, and nectar), 4% for foods in two categories (fruit and leaves), and 79% for foods in only one (fruit), 12% only

Table l.

Adaptability of Ruffed Lemurs List of food species eaten by Varecia variegata at Manombo forest

Importance

Family

Scientific name

Vernacular name

Part eatena

value

Annonaceae

Monanthotaxis pilosa

vahatsimatra

Fr

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