Exploración en el niños verbal o Preescolar

Since there are no written histories from extinct hominan ancestors, we are left to interpret the fossil record to the best of our ability to understand their general behavior. To determine the climate and habitat used by hominans, methods from biogeography are used. Biogeography presents climatic evidence over the history of the Earth. In studying savanna- dwelling chimpanzees, I ultimately relate the importance of their habitat to human evolution in terms of ecology and behavior. Most importantly, the diet of the savanna chimpanzees may be more relevant in a referential model for hominan diet compared to chimpanzees living in a more forested habitat.

Africa contains many different habitats. Forests require a high mean annual rainfall and long wet seasons having tall trees making multiple canopies (Reed & Rector 2007). There are four classification of savanna and all have less mean annual rainfall than forest: woodland, bushland, shrubland, and grassland (Reed & Rector 2007). Woodland savannas had a grass-based understory with a sparser canopy than forests and can be considered open or closed based on the degree of canopy cover (Reed & Rector 2007). Bushlands have trees that reach 3-9 meters tall with few grasses, but may contain more fruit that woodland (Reed

& Rector 2007, Sept 1994). Shrublands have one to three meter tall trees and grassland has very few trees, abundant rain in certain months and is burned regularly (Reed & Rector 2007). Savannas can contain several of these microhabitats and are considered mosaic (Reed & Rector 2007). Seasonal lengths differs across Africa but is defined as wet versus dry in the amount of rainfall.

From 4.2-3 mya, several species of Australopithecus were living in mosaic

environments composed of closed and open woodlands, bushlands, and forests (Bobe & Eck 2001, Reed 1997, Reed & Rector 2007). A few sites were more open and dry, such as Allia Bay (A. anamensis) and Koobi Fora (A. afarensis) in East Africa (Reed 1997, Reed & Rector 2007, Wynn 2000). In South Africa, Sterfontein 4 where A. africanus is found is also drier (Reed & Rector 2007).

Between 3.0-2.5 mya new genera appear, that of Paranthropus and Homo. During this time period hominans were living in open woodlands, bushlands, and shrublands with wetlands (Bobe & Eck 2001, Reed 1997, Reed & Rector 2007). These habitats possibly had more water available than they contain today (Reed & Rector 2007). After 2 mya, the habitats became more open, but there were two periods of extensive grasslands at 1.7 mya and 1.2 mya with subsequent returns to woodlands and bushlands (Cerling 1992 , Reed 1997)

Australopithecus, Paranthropus, and early Homo species all lived in mosaic habitats ranging from more closed (Australopithecus) to more open (Paranthropus and early Homo). In terms of how hominans responded to climate changes and their selection of a habitat in which to exist, three hypotheses have been postulated: the savanna hypothesis (Dart 1925), the turnover pulse hypothesis (Vrba 1992, 1995), and the variability selection hypothesis (Potts 1998).

Through the savanna hypothesis researchers attempt to explain the divergence of humans from chimpanzees as related to habitat. First proposed by Dart in 1925, this hypothesis postulated that human divergence was directly related to the spread of open savannas, while the other great apes remained among the dense forests. Recently, this hypothesis has been disputed with new evidence that open savanna habitats were not as prominent during early hominan (Australopithecine) existence and that they mainly lived in a closed habitat (Bobe & Behrensmeyer 2004, Reed 1997, Strait & Wood 1999). Reed (1997) used changes in mammal morphology of assemblages associated with hominan species in order to reconstruct paleo-habitats. It was found that gracile Australopithecines lived in more closed habitats with significant water content, while Paranthropus species (also known as robust Australopithecines) lived in more open areas which always included wetlands, and Homo existed in an even more open region with grasslands (Reed 1997). This lends further support in falsifying the traditional savanna hypothesis (Reed 1997). Open savanna habitats were not abundant until about 1.7 million years ago (mya) (Cerling 1992) and have only been associated with Paranthropus and early Homo species (Bobe & Behrensmeyer 2004,

Bromage & Schrenk 1995, Reed 1997, Wesselman 1995). Bobe and Behrensmeyer (2004) suggest that instead of explaining the divergence of hominans, the savanna hypothesis could be used to explain the evolution of the genus Homo.

The faunal turnover hypothesis adds to the savanna hypothesis, stating that savannas were important to human evolution, but emphasizing, in addition, the pulses of faunal turnover in mammal taxa (Vrba 1992, 1995). Faunal turnover is characterized by evolution, extinction, and immigration. This hypothesis links climatic changes to that of faunal

climate related to the rise and fall of sea levels due to glacial events (Opdyke 1995). Two collections of micro-mammal remains at Kabwe displayed a high proportion of savanna woodland habitat species during the Early and Middle Pleistocene when Homo species occupied the area during interglacial periods seeking refuge from drought (Avery 2003). Avery (2003) suggested that Kabwe was located within a migration route for Homo species during this time, and that they migrated along rivers and lakes with tropical and subtropical habitats, rather than the rift valleys. The major dispersal events of hominans from East to South Africa and the Malawi Rift occurred between four to seven different times and all but one hominan dispersal events followed other dispersing mammals (Strait & Wood 1999). This relationship between mammals and hominans provides support for the turnover pulse hypothesis. Homo habilis and possibly Paranthropus robustus dispersed in a different direction from mammals, suggesting that these hominans possessed different anatomical or behavioral adaptations to allow for environmental fluxes (Strait & Wood 1999). This departure from a mammalian trend may lend support to a more environmental hypothesis. Further evidence for the faunal turnover hypothesis is that open savanna habitat types in Africa were not inhabited by Paranthropus and early Homo until about 1.8mya, while earlier Australopithecines lived in wooded habitats and had some morphological traits associated with an arboreal lifestyle (Bromage & Schrenk 1995).

A different hypothesis that has been presented is the variability selection hypothesis. This postulates that human emergence was brought about by the increasing variability of the climate and environment during the Plio-Pleistocene (Potts 1998). Several studies have provided evidence for this hypothesis. Bobe and Behrensmeyer (2004) examined fossil mammals from the Plio-Pleistocene in Kenya and Ethiopia dating from four to one million

years ago. They concluded that there were profound faunal changes and Paranthropus and Homo species existed during a high faunal turnover from 2.8-2.6 mya and 2.4-2.2 mya in Kenya and Ethiopia (Bobe & Behrensmeyer 2004). Homo erectus arrived at about 2 mya with a large increase in grassland habitat. Also, fauna occurred periodically with 100,000 year shifts that coincided with Homo inhabitation starting from 2.5 mya (Bobe &

Behrensmeyer 2004). This last finding provides support for the variability selection

hypothesis. Considering global environmental conditions during the Cenozoic, Potts (1998) explains that hominan sites demonstrate 1) large shifts of habitats, 2) a lack of agreement between environmental conditions and important adaptations to habitat, 3) extensive changes in the climatic conditions that cannot be explained solely by the seasonality hypothesis, and 4) hominans existed in diverse habitats during long periods of environmental change. All of these factors support the variability selection hypothesis (Potts 1998).

All three hypotheses may prove useful regarding our understanding of human evolution. The savanna hypothesis might be important for the explanation of Homo

evolution. Many studies provide support of the faunal turnover hypothesis in that hominans and other mammals responded similarly to the environment. The variability selection hypothesis also receives support from different studies; hominan evolution was affected by the variability of climate changes that were presented at the time of their evolution. It cannot be said that human evolution was simple; therefore we may find various different scenarios to explain the process. Humans are a complex species, and the fossil record reveals

incomplete snapshots of the past. A recent finding has demonstrated evidence for the

sympatric use of habitat by both chimpanzees and Homo ergaster. McBrearty and Jablonski (2005) describe the first chimpanzee fossil discovered. The East African Rift Valley in

Kenya provides data indicating co-habitation between later Homo species and chimpanzees, extending chimpanzees’ ancient boundaries further east than originally thought (McBrearty & Jablonski 2005).

The Fongoli chimpanzees live in a mosaic savanna habitat consisting of closed and open woodland, grassland, and small patches of forest (Table 2.6) (see Chapter Four). They use mostly open habitats for travel, but do not spend much time within them (Pruetz & Bertolani, in press). This may be in part to thermoregulation issues such as the reduction of direct sun exposure (Pruetz & Bertolani, in press). Fongoli provides a unique opportunity to understand the behavior of chimpanzees living in an open mosaic savanna environment. Studying the ecological context of those behaviors will provide essential evidence to be used in a referential model for hominan evolution (sensu Moore 1996). My research examines the insectivorous diet of the Fongoli chimpanzees. Limited research has been done on this area of the diet in hominans.

Table 2.6: Comparing defined habitat classifications to those used in this study at Fongoli, Senegal.

Habitat at Fongoli1 Reed & Rector's (2007) four

classifications of savanna Bobe & Eck 2001 Forest ecotone Non-savanna3 _Forest Gallery forest Tall grassland Grassland Grassland Short grassland

Woodland (open and closed) Woodland Woodland

Bamboo woodland Woodland/Bushland Woodland/Bushland Thicket2 _{woodland Bushland/Shrubland Bushland/Shrubland} 1 _{Used in this research, described in Chapter Three}

2 _{Used by Pruetz & Bertolani, in press} 3 _{Reed 1997 considered this forest}