fnctId=thesis,fnctNo=367
A Global Environmental Perspective on the Early Human Ecological Niche
- 작성자
- 기후시스템전공
- 저자
- Elke Cornelia Elizabeth Zeller
- 발행사항
- 발행일
- 2024-10
- 저널명
- 국문초록
- 영문초록
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The genus Homo has evolved throughout the last 3 million years, gradually expanding its geographic range and the dierent types of environments it could inhabit while coping with the large changes in climate that occurred over this time period. Climate variability played an important role in hominin evolution and migration, the extent to which this occurred and the mechanistic details of the processes involved are active areas of research. While previous work investigated the direct impact of climate variables on hominins, particularly temperature and precipitation, the indirect eect of climate via its determination of biome types on a global scale has been under-explored due to the limited availability of data. In this dissertation, we shed light on the role of vegetation and ecosystem diversity on hominin adaptation and migration, addressing: (1) The biome niche of the genus Homo and how it changed over time; (2) Whether our ancestors preferred homogenous environments or if they adapted to diverse ones; (3) The underlying environmental drivers of the early human biome niche. To accomplish this, we used a 3-million-year quasi-transient paleo climate and a forced oine biome simulation combined with an extensive hominin fossil/archeological database covering six species of the genus Homo. Instead of modeling the hominin climate niche using species distribution models, statistics are applied directly to capture the climate and environment at the location and estimated age corresponding to each of the fossils or tools within the hominin database. The preferred habitats of dierent hominin groups can be identified by connecting the hominin data with the simulated biome types at the place and time where hominins likely occurred in the past. The method reveals that early African hominins (H. habilis and H. ergaster) predominantly lived in open environments, such as grassland and dry shrubland, but were present in tropical forests. Migrating into Eurasia, hominins adapted to a broader range of biomes over time. H. erectus was the first hominin to occupy Europe; in doing so they shifted their primary biome(s) from grassland and dry scrubland to temperate forest and also began adapting to boreal forest. Later species could withstand even harsher environments such as deserts and tundra, with H. sapiens being the only species that adapted to all biomes. The pattern of biome expansion demonstrates hominins’ ability to adapt over time to increasingly varied and dicult environments. Given that members of the genus Homo demonstrate flexibility in the environments they inhabited, it makes sense to ask if they preferred to live in areas that had access to a wide variety of environments. Living near dierent vegetation types would increase the biodiversity in the area, providing additional food sources, and increase resilience to climate change, as dierent plant types have dierent climatic niches. A variety of accessible vegetation would be increasingly beneficial for species that were more widely adapted to dierent environments. To investigate whether hominins indeed had a preference for mosaic environments, the biome diversity within the 3-million-year simulation was measured by counting the number of biomes present in a 3x3 square of grid cells. Comparing the biome diversity centered at hominin locations to that of nearby areas showed that hominins actively selected for diverse environments. These quantitative results lead to a new diversity hypothesis: Homo species were specially equipped to adapt to landscape mosaics. Understanding the link between hominin evolution and habitat preference led us to further examine what aspects of the landscape itself led to increases in biome diversity. We found that most of the hominin sites lay in mid-terrain roughness areas and that terrain roughness is positively correlated with biome diversity. Looking further into the relationship between biome diversity, terrain roughness, and the climatic variables, temperature and precipitation, we see that roughness is a more important predictor of biome diversity than climate. These results suggest that the benefits related to potentially higher biome diversity overcome the costs of movement for all but the steepest terrain. Further exploration of the time-evolving hominin roughness niche reveals that there were two periods of expansion during which hominins started occupying increasingly rougher terrains. The first time was between 2?1.1 million years ago and the second time between 0.9?0.1 million years ago. The contraction of the ecological niche in between coincided with the Mid-Pleistocene Transition and was mostly prevalent within Africa. The results aligned with other evidence that suggests MidPleistocene Transition climate variability may have played a major role in hominin evolution. Taken together, these studies provide a more detailed picture of the gradual adaptation of hominin species to environments with an increasingly wide range of climate conditions and biome types. Being able to utilize multiple types of vegetation could have both increased the available resources, providing a competitive advantage and increased climate resilience, as distinct plant species thrive in dierent climate niches. The results further demonstrate that a particularly useful adaptation was the ability to navigate rough terrain, as varied topography results in sharp climate gradients and diverse vegetation nearby. Employing such adaptive strategies allowed hominin species to spread out of Africa into Eurasia, eventually allowing our own species to colonize nearly every environment globally.
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