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Habitat Fragmentation • Process of breaking contiguous unit into smaller pieces; area & distance components Habitat Fragmentation 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 1st order effects HABITAT FRAGMENTATION GroundNesting Birds - Abundance – - Distribution Avian Competitors Avian Prey Brood Parasites Predators - Abundance + - Distribution - Foraging Behaviors – + – + 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 Area of Reserve (km^2) (A) black bear (F) lion (I) African wild dog (J) grizzly bear Habitat Fragmentation • area-sensitive species: species that require minimum patch size for daily life requirements • Edge effects: Edge Effects 250 m 250 m 31% 64% Total Area = 1 km2 250 m 14% Total Area = 5 km2 Total Area = 0.5 km2 Edge Effects 250 m 250 m 31% 64% Total Area = 1 km2 250 m 14% Total Area = 5 km2 Total Area = 0.5 km2 Edge Effects 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 Area of Reserve (km^2) (A) black bear (F) lion (I) African wild dog (J) grizzly bear Habitat Fragmentation: SpeciesSpecific 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 multistage life cycle?) Habitat Fragmentation: SpeciesSpecific 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: SpeciesSpecific Sensitivity? Generalizations are a good start (= hypotheses?), but a little more complex than that…… Swihart et al. 2003. 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