Barriers and dispersal are fundamental concepts in zoogeography, the study of the geographical distribution of animals. They influence how species spread, adapt, and evolve in different regions.
Barriers in Zoogeography: Barriers restrict or prevent the movement of species, influencing their distribution. They can be classified into:
a. Physical (Geographic) Barriers: Oceans & Seas: Prevent land animals from crossing.
Example: The Wallace Line separates Asian and Australian fauna.
Mountains: Act as barriers for lowland species.
Example: The Himalayas prevent movement between India and Tibet.
Deserts: Limit species adapted to humid environments.
Example: The Sahara Desert restricts the movement of many African species.
b. Climatic Barriers: Temperature, humidity, and rainfall influence animal distribution.
Example: Tropical species may not survive in polar regions.
c. Ecological Barriers: Differences in food availability, competition, and predation affect movement.
Example: A rainforest species may not survive in a savanna due to lack of suitable resources.
d. Biological Barriers: Factors like reproductive limitations, behaviors, and adaptability.
Example: Amphibians, which need moisture for reproduction, cannot colonize dry regions.
e. Anthropogenic Barriers: Human-made structures such as roads, cities, and deforestation disrupt movement.
Example: Urbanization fragments natural habitats, affecting species like large mammals.
2. Dispersal in Zoogeography
Dispersal refers to the movement of organisms from one geographic area to another, leading to the spread of species. It can be classified into:
a. Active Dispersal
• Animals move by their own means (e.g., flying, swimming, walking).
• Example: Birds migrating across continents.
b. Passive Dispersal
• Animals are carried by external forces like wind, water currents, or human activity.
• Example: Insects transported by wind or marine organisms drifting on ocean currents.
3. Effects of Barriers and Dispersal on Zoogeographic Regions
Barriers contribute to speciation by isolating populations, leading to evolution.
Dispersal allows species to colonize new areas, leading to biogeographic patterns like endemism and invasion.