Habitat Fragmentation Process of breaking contiguous unit into smaller pieces; area & distance components Habitat Fragmentation Process of breaking contiguous unit into smaller pieces; area & distance components (includes habitat loss?) Leads to: Habitat Fragmentation Community & Ecosystem processes altered Habitat Fragmentation First-Order Effects: fragmentation leads to change in a species abundance and/or distribution Habitat Fragmentation Higher-Order Effects: fragmentation indirectly leads to change in a species abundance and/or distribution via altered species interactions Altered community-level interactions relates to 1 st order effects Predators - Abundance - Distribution - Foraging Behaviors Avian Competitors Avian Prey Brood Parasites HABITAT FRAGMENTATION Ground- Nesting Birds - Abundance - Distribution Parasites - Abundance - Distribution REPRODUCTIVE SUCCESS + + + Formation of Terrestrial Islands #patches Patch isolation Patch size Edge Implications with Diseases Theory predicts that small populations > P(extinction) by random fluctuations in demography and loss of genetic diversity through genetic drift Isolation effects Carnivores & Reserves (A) black bear (F) lion (I) African wild dog (J) grizzly bear Area of Reserve (km^2) Habitat Fragmentation area-sensitive species: species that require minimum patch size for daily life requirements Edge effects: Edge Effects Total Area = 5 km m 64% Total Area = 1 km m 31% Total Area = 0.5 km m 14% Edge Effects Total Area = 5 km m 64% Total Area = 1 km m31% Total Area = 0.5 km m 14% Edge Effects Habitat surrounding a patch can: -change abiotic conditions; e.g., temp. -change biotic interactions, e.g., predation Example of nest predation = edge effect of approximately 50 m into forest patch Carnivores & Reserves (A) black bear (F) lion (I) African wild dog (J) grizzly bear Area of Reserve (km^2) Habitat Fragmentation: Species- Specific Sensitivity? Rare species = more vulnerable Wide ranging species = large-area requirements Species with reduced mobility = more vulnerable Species with low fecundity (related to rarity?) Species with short life cycle (or multi- stage life cycle?) Habitat Fragmentation: Species- Specific Sensitivity? Ground-nesting birds may be more vulnerable (30-60% reduction in last 25 yrs) Interior-dependent species Species vulnerable to human exploitation or disturbance Specialist species? Habitat Fragmentation: Species- Specific Sensitivity? Generalizations are a good start (= hypotheses?), but a little more complex than that Swihart et al Diversity and Distributions 9:1-8. Differential Sensitivities to Habitat Alteration Niche breadth (diet & habitat) inverse relation Range periphery = more sensitive (W & N) Body size = mobility (allometric relation) Social and territorial behavior (limited K) Swihart et al. 2003