Module 2.2

Introduction to Habitat Fragmentation

• Definition: Habitat fragmentation refers to large expanses of habitat that have been divided into smaller patches, isolated by matrices of different habitats.

• Non-contiguity: Causes issues for wildlife as it inhibits natural movements, especially for migratory species or those with large home ranges.

• Genetic exchange: Restricts movement necessary for genetic exchange, leading to the formation of micro-populations vulnerable to diseases and other anthropogenic stressors.

Concept of Landscapes

• Definition of landscape: Comprises various ecosystems, spatially heterogeneous with different land use types, including natural and developed areas.

• Mathematical modeling: Landscapes are of particular interest in predictive modeling for ecological studies.

• Fragmentation visualization: Fragmented habitats may consist of small patches that hinder species exchange, visually depicted through graphics illustrating ecosystem composition.

Island Biogeography and Species Diversity

• Distance effect: Isolated patches tend to have decreased species diversity, affecting populations, metapopulations, communities, and entire ecosystems.

• Metapopulation concept: Defined as distinct groups of a species (e.g., leopards in separate ecosystems) contributing to overall diversity within a landscape.

• Disease risk: Isolated populations have higher risks of disease invasion and extinction due to limited genetic exchange.

Edge Effects in Fragmented Habitats

• Definition: The edge effect illustrates the transition zone where different ecosystems or land uses meet, particularly prominent in fragmented habitats.

• Fragmentation and edge increase: The more fragmented a habitat, the greater the edge effect and the higher prevalence of generalist species, often at the expense of interior specialists.

• Species dynamics: As habitats fragment, generalists thrive, while interior specialists decline, altering the ecosystem balance.

Distinction Between Habitat Loss and Fragmentation

• Habitat loss: Refers to the complete destruction of an ecosystem, while fragmentation indicates disruption of a habitat that still exists albeit in smaller portions.

• Human impact: Both phenomena are influenced by anthropogenic factors such as deforestation, urbanization, and agriculture.

Mathematical Modeling in Disease Dynamics

• SIR model: Stands for Susceptible, Infected, and Recovered individuals used to model infectious disease dynamics.

• Variables: The model considers susceptibility, infection rates, recovery dynamics, and can include carrier states impacting transmission.

• Factors affecting disease prevalence: Birth/death rates, virulence of diseases, and population immunity contribute to the dynamics modeled in SIR equations.

Fragmentation’s Impact on Disease Ecology

• Density and distribution: Habitat fragmentation alters species density, abundance, and distribution, directly affecting disease transmission patterns.

• Generalist species as reservoirs: White-footed mice and raccoons display higher densities in fragmented habitats, leading to increased zoonotic disease risks, such as Lyme disease and roundworm from raccoons.

• Dilution effect: Increased biodiversity can lower the prevalence of zoonotic diseases, emphasizing the need for ecological balance to mitigate risks.

Criteria for the Dilution Effect

1. Pathogen must infect several host species, including humans.

2. Host competency varies, influencing infectious transmission.

3. The dominant reservoir host must be a significant component in the host community.

4. Reservoi with lower competence are more common in biodiverse areas.

Generalist vs. Specialist Species

• Generalists: Adaptable species like raccoons that thrive in altered habitats and can serve as reservoirs for diseases.

• Specialists: Species with narrow ecological niches, typically seen in specific natural habitats, less adaptable to change.

• Increased risk of pathogen exposure tied to generalist prevalence amid habitat fragmentation.

Impact of Invasive Species and Abiotic Changes

• Success of invasive species: Typically flourish in fragmented habitats, posing risks to local biodiversity.

• Changes in local microclimates: Fragmented ecosystems may experience increased solar radiation and decreased moisture, further impacting species and disease dynamics.

Genetic Diversity and Extinction Risks

• Lower genetic diversity: Isolated populations possess decreased genetic resilience, risking extinction events.

• Example of cheetahs: Low genetic diversity leads to heightened disease susceptibility, particularly in captivity.

Conclusion and Future Directions

• Relationship with poaching: Habitat fragmentation opens up ecosystems for human activities like bushmeat hunting, increasing zoonotic risks.

• Upcoming discussions: Further exploration into the bushmeat trade and its implications on wildlife health and conservation efforts in the next lectures.