Interactions between species are thought to be one of the largest factors of natural selection. Prior research has shown that primate species are constantly interacting, and that these interactions are not always peaceful or playful. Studies from La Suerte Biological Station have shown that howler monkeys (Alouatta palliata) and spider monkeys (Ateles geoffroyi) displace each other in order to get to the food resources. Other times, the two species are seen playing with each other. Alouatta palliata appear to be tolerant of other resident males but aggressive towards nonresident males. Ateles geoffroyi have been known to use fission-fusion dynamics which decrease competition and aggression. Whether these patterns of interactions are also found at La Selva Research Station is unknown. This study will examine the interactions within species and between species of Alouatta palliata and Ateles geoffroyi. I predict that interactions within Alouatta palliata groups will be more affiliative compared to interactions with Ateles geoffroyi groups. This research will take place at La Selva Research Station in May 2022. La Selva Research Station is located in the lowlands of the Caribbean in Costa Rica and is surrounded by the Sarapiqui and Puerto Viejo Rivers totaling about 103.89 km. Due to the high amount of rainfall, La Selva Research Station is covered with tropical pre-montane wet forest, which is more commonly known as rainforest. La Selva Research Station is home to Alouatta palliata, Ateles geoffroyi, and Cebus imitator. La Selva Research Station also has an expansive number of trails totaling in 50 km. Alouatta palliata are recognized by dark brown/black coloring with a lighter color along their sides and back. Males average about 9.8 kg while females average 5 kg. Ateles geoffroyi have dark hair with lighter coloring on their chest and stomach. Males and females both average between 6 and 9 kg. For my data collection I will be using instantaneous scan sampling with an interval of 30 seconds. I will alternate between Alouatta palliata and Ateles geoffroyi each day. For each scan I will record whether behaviors are solitary, affiliative, or aggressive, and for social behaviors I will record the partner. I will compare the amount of affiliation and aggression within groups and between groups.
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