Geographic Distribution of Animal Life

Global Distribution of Animals

• Uneven Distribution Patterns: Animal species are not spread randomly; their distribution is highly uneven due to a complex interaction of environmental, evolutionary, historical, and ecological factors.
• Climatic Variation: Climate is a primary predictor of where species live. Temperature and precipitation define major biomes like tropical forests and tundras, and species are restricted by physiological limits such as heat tolerance and water requirements.
• Habitat Heterogeneity: Different regions offer varied habitats (forests, wetlands, grasslands). A species adapted to one habitat, such as a freshwater fish, often cannot colonize another, such as the ocean.
• Historical and Evolutionary Processes: Continental drift has created distinct biogeographic realms over millions of years. Historical events like ice ages have forced species to shift or fragment their ranges, leading to endemism—where species like Madagascar's lemurs are found nowhere else.
• Vicariance and Barriers: Vicariance occurs when a species' range is split by a physical barrier like a rising mountain range or changing river course, leading to genetic divergence and speciation. Physical barriers like oceans and deserts also limit movement, which is why islands often have unique faunas.
• Biotic Interactions: Relationships such as competition, predation, and mutualism shape where species can thrive. For example, some species can only exist where their specific pollinators or symbionts are present.
• Human Activities: Humans have significantly altered distributions through habitat destruction, overexploitation, and the introduction of invasive species. Additionally, human-driven climate change is forcing species to shift their ranges toward the poles or higher elevations.

Core Biogeographic Concepts

• Latitudinal Diversity Gradient: Species richness is generally highest at the equator and declines toward the poles due to stable climates and long evolutionary histories in tropical regions.
• Dispersal and Colonisation: Dispersal is the movement of individuals away from their birthplace. Its success depends on the species' ability (e.g., birds vs. amphibians) and leads to colonisation when a viable population is established in a new area.
• Niche Theory:
  • Fundamental Niche: The full range of conditions under which a species can survive and reproduce.
  • Realised Niche: The actual portion of the niche a species occupies, limited by factors like competition and dispersal barriers.

Biogeography of Nigeria

• Climatic Zones: Nigeria spans from the humid tropical south (over 3,000 mm of rain), supporting primates and the Ibadan malimbe, to the semi-arid Sahel north (less than 500 mm of rain), which hosts drought-tolerant fauna.
• Topography as "Ecological Islands": Mountainous regions like the Jos, Mambilla, and Obudu Plateaus create isolated habitats with cooler climates. These areas support montane grasslands and relic forests that harbor endemic species and highland-adapted birds and amphibians.
• Hydrology and Wetlands: The Niger and Benue Rivers form extensive floodplain and wetland habitats. Seasonal wetlands like the Hadejia-Nguru floodplains serve as vital migratory stopovers and breeding grounds for Afro-Palaearctic waterbirds.
• Vegetation Zones:
  • Mangrove Forests: Vital for manatees and mudskippers in the Niger Delta.
  • Lowland Rainforests: Support endangered primates, forest elephants, and pangolins.
  • Savannas: Home to large mammals like buffalo and ground-nesting birds.
  • Forest–Savanna Mosaics: Provide mixed resources that allow for overlapping ranges of both forest and savanna species.