Impacts of Habitat Fragmentation on Species Diversity

1. Introduction – Landscape Ecology • Landscape Ecology: Study of landscape structure and processes. • Landscape: Heterogeneous area composed of several ecosystems. • Landscape Elements: Visually distinctive patches in an ecosystem.

2. Vancouver Island marmot(Marmota vancouverensis) ~100 left Isolated from hoary and Olympic marmots

3. Vancouver Island marmot(Marmota vancouverensis) Natural tree succession

4. Vancouver Island marmot(Marmota vancouverensis) • Logging – disjunct patches • - max. dispersal = 7 km • Climate • Prey-Predator Dynamics

5. Human Land Use Practices • Agriculture • Suburban Development • Let’s pick on Indiana: • 97% of land in state = privately-owned • In central Indiana, • 70+% of land in row crop • <10% in forest • Urban sprawl intensifying

6. Human Impacts • Ecosystem simplification: elimination of species from food webs via human alterations to land • Example: vertebrate communities in ag. landscapes

8. Intensive Agriculture & Clean Farming

9. Timber Extraction & Fragmentation

10. Roads: Formation of Barriers in Landscapes

11. Formation of Terrestrial “Islands”

12. Habitat Fragmentation • Process of breaking contiguous unit into smaller pieces; area & distance components • Leads to: • < remnant patch size • > edge:interior ratios • > patch isolation • < connectivity • Community & Ecosystem processes altered

13. Formation of Terrestrial “Islands”

15. Habitat Loss vs. Habitat Fragmentation

16. Patch size #patches Patch isolation Edge

18. What about aquatic systems?

19. What about aquatic systems? Con.Bio 12(6)

20. Habitat Fragmentation • area-sensitive species: species that require minimum patch size for daily life requirements • Edge effects: influence of factors from outside of a patch

21. Increased Edge Habitat

22. Increased Edge Habitat

23. 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

24. Habitat Fragmentation • First-Order Effects: fragmentation leads to change in a species’ abundance and/or distribution

25. Habitat Fragmentation • Higher-Order Effects: fragmentation indirectly leads to change in a species abundance and/or distribution via altered species interactions

26. HABITAT FRAGMENTATION Predators - Abundance - Distribution - Foraging Behaviors + Ground-Nesting Birds - Abundance - Distribution – – – Avian Competitors Avian Prey Brood Parasites + + Parasites - Abundance - Distribution REPRODUCTIVE SUCCESS

27. 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?)

28. 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?

29. Habitat Fragmentation: Species-Specific Sensitivity? • Generalizations are a good start • (= hypotheses?), but a little more complex than that……

30. Gehring and Swihart. 2003. Biological Conservation 109:283-295

31. Spatial and Temporal Ecology of Raccoons Gehring et al. In prep.

32. Swihart et al. 2003. Diversity and Distributions 9:1-8.

33. Brown and Litvaitis. 1995. Canadian Journal of Zoology 73:1005-1011

34. Implications of Changes in Scale Insects sampled at 10-m intervals for 100 m

35. Implications of Changes in Scale Insects sampled at 2000-m intervals for 20,000 m

36. Landscape Processes • Landscape structure influences processes such as the flow of energy, materials, and species between the ecosystem within a landscape.

37. Landscape Structure and Dispersal of Small Mammals

38. Habitat Patch Size and Isolation and Density of Butterfly Populations

39. Organisms and Landscape Structure • African elephants knock down tress. • Change woodland to grassland. • Kangaroo Rats dig burrow systems that modify soil structure and plant distributions. • Beavers cut trees, build dams and flood surrounding landscape. • At one time, beavers modified nearly all temperate stream valleys in Northern Hemisphere.

40. Organisms and Landscape Structure • Johnston and Naiman documented substantial effects of beavers on landscape structure. • Over 63 yrs, area created by beavers increased from 200 ha to 2,661 ha. • Changed boreal forest landscape to complex mosaic. Skip

41. Organisms and Landscape Structure • Beaver activity between 1927-1988 increased quantity of most major ions and nutrients in impounded areas. Three possible explanations: • Impounded areas may trap materials. • Rising waters captured nutrients formally held in vegetation. • Habitats created by beavers may promote nutrient retention by altering biogeochemical processes. Skip

42. Introduction – Geographical Ecology • MacArthur defined geographical ecology as the search for patterns of plant and animal life that can be put on a map. • Above level of landscape ecology. • Vast breadth • Chapter only focuses on a few aspects.

43. Oceanic Island = Terrestrial Island ?????

44. Island Area and Species Richness • Preston found fewest bird species live on smallest islands and most species on largest islands. • Nilsson et.al. found island area was best single predictor of species richness among woody plants, carabid beetles, and land snails. Skip

45. Island Area and Species Richness

46. Species-Area Relationship • S = cAz • S = # of species • A = island area • Positive correlation between island size & number of species • Applies to terrestrial “islands” also

48. Habitat Patches on Continents: Mountain Islands • As Pleistocene ended and climate warmed, forest and alpine habitats contracted to the tops of high mountains across American Southwest. • Woodlands, grasslands, and desert scrub, invaded lower elevations. • Once continuous forest converted to series of island-like fragments associated with mountains: Montane. Skip

49. Lakes as Islands • Lakes can be considered as habitat islands. • Differ widely by degree of isolation. • Tonn and Magnuson found the number of species increases with the area of an insular environment. • Barbour and Brown found positive relationship between area and fish species richness. Skip

50. Lakes as Islands Skip