Biogeography and Biodiversity

Define evolutionary history: Understand how historical events influence modern species distributions and biogeographic regions.
Key Historical Processes:
- Plate tectonics
- Vicariance
- Dispersal
Compare and contrast vicariance and dispersal:
- Explain methods to identify whether vicariance or dispersal has occurred.
Hypotheses for Latitudinal Biodiversity Gradient:
- Suggest explanations for the increased biodiversity typically found in lower latitudes.
Species-Area Relationship:
- Define this concept and apply it to predict species counts on islands.
Theory of Island Biogeography:
- Explore the balance between immigration and extinction rates.
- Discuss the influences of island size and proximity to mainland on these rates.
Edge Effects and Habitat Fragmentation:
- Define these concepts and make recommendations for conservation to minimize their impacts.

Definition: Evolutionary history refers to the origins of a species, including when and where it originated and the subsequent events that shaped its current distribution.
Influence of Geological History: Observations of species distribution today can provide insights into historical geographical and geological events that have influenced them.

Alfred Russel Wallace conducted extensive travels in the Malay Archipelago, noting significant patterns in species distributions.
Observed that the differences in species and communities across islands could not solely be explained by geological and climatic differences.
Inference: Wallace concluded that the depth of water separating these regions was a critical factor affecting biodiversity.

Earth can be segmented into specific biogeographic regions characterized by distinct species assemblages.
Boundaries: These regions are marked by sharp changes in species composition over short distances.
Barriers: Historical and current barriers prevent dispersal between these regions, including oceans and mountains.

Examples of Barriers:
- Oceans
- Mountains
- Climatic gradients
Case Study: The division between the Antarctic and Neo-tropical regions in South America exemplifies a climatic barrier, limiting organisms adapted to tropical climates from surviving in colder conditions further south.

Major Influence: The formation and separation of continents through plate tectonics significantly influences the distribution of biodiversity.
Historical Context: During the Triassic and Jurassic periods, the supercontinent Pangaea fragmented, resulting in the formation of Gondwana and Laurasia, subsequently leading to the current continental configurations.

Fossils provide critical evidence for reconstructing historical tectonic movements and positions.
Inference: If groups of organisms are found on multiple continents, it suggests a common ancestry during the time of Pangaea, indicating their evolutionary lineage dates back to this supercontinent.

Vicariance: This occurs when a physical barrier forms, hindering dispersal and dividing a species into separated populations.
Dispersal: Involves members of a species moving across an existing barrier to establish new populations.
Example (Vicariance): Fish species in North America were isolated due to the division of the epicontinental seaway by Pleistocene glaciation.
Example (Dispersal): The case of the tiger chameleon, which is found on the Seychelles Islands but adapted from a relative on mainland Africa.

Biodiversity is typically greater in tropical regions compared to higher latitudes, although there are exceptions like seabirds.

Species Diversification Rate Hypothesis: In the tropics, higher speciation rates and lower extinction rates are attributed to larger geographic areas and a stable climate.
Species Diversification Time Hypothesis: The tropics have been climatically stable over extended periods, allowing longer durations for speciation.
Productivity Hypothesis: Greater resource availability promotes species diversification, while increased productivity in oceans at high latitudes can explain certain seabird diversity patterns.

Pattern Recognition: Larger islands tend to support greater species diversity.
Influencing Factors:
- Island size affects resource availability and competition potential, with smaller islands facing higher extinction rates.
- Distance to the mainland or large islands impacts species immigration probabilities, where farther islands have reduced chances of new species reaching them.

The theory proposes that the number of species residing on an island reflects a balance between immigration rates and extinction rates among resident species.
Resultantly, an equilibrium number of species is maintained despite ongoing turnover.

Habitat destruction by humans creates isolated patches of functional habitats, which leads to increased fragmentation.
Definition: Habitat fragmentation results in isolated habitats surrounded by areas unsuitable for the species.

Edge Effects: The transition zones created by fragmentation expose species to various threats, like intense heat, fires, hunting pressures, and invasive species.
Consequence: Edge conditions often reduce the effective habitat size, resulting in diminished viability for species residing there and reducing inter-patch immigration rates.

Studies measured biodiversity across different-sized forest islands bordered by deforested areas.
Results indicated smaller fragments housed significantly fewer species than larger ones. Notably, even narrow distances (as short as 80 meters) between fragments could lead to isolation and species loss.
Application of Concepts: The species-area relationship and theories of island biogeography can guide conservation strategies to optimize protected area sizes and configurations for biodiversity preservation.