- Slides: 71
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.
Vancouver Island marmot (Marmota vancouverensis) ~100 left Isolated from hoary and Olympic marmots
Vancouver Island marmot (Marmota vancouverensis) Natural tree succession
Vancouver Island marmot (Marmota vancouverensis) • Logging – disjunct patches - max. dispersal = 7 km • Climate • Prey-Predator Dynamics
Human Land Use Practices 1) Agriculture 2) Suburban Development Let’s pick on Indiana: • • 97% of land in state = privatelyowned In central Indiana, • 70+% of land in row crop • <10% in forest • Urban sprawl intensifying
Human Impacts Ecosystem simplification: elimination of species from food webs via human alterations to land Example: vertebrate communities in ag. landscapes
Intensive Agriculture & Clean Farming
Timber Extraction & Fragmentation
Roads: Formation of Barriers in Landscapes
Formation of Terrestrial “Islands”
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
Formation of Terrestrial “Islands”
Habitat Loss vs. Habitat Fragmentation
#patches Patch isolation Patch size Edge
What about aquatic systems?
What about aquatic systems? Con. Bio 12(6)
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
Increased Edge Habitat
Increased Edge Habitat
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
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
HABITAT FRAGMENTATION – Avian Competitors Avian Prey Brood Parasites Ground. Nesting Birds - Abundance - Distribution Predators - Abundance + - Distribution - Foraging Behaviors – + REPRODUCTIVE SUCCESS – + Parasites - Abundance - Distribution
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 multistage 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……
Gehring and Swihart. 2003. Biological Conservation 109: 283 -295
Spatial and Temporal Ecology of Raccoons Gehring et al. In prep.
Swihart et al. 2003. Diversity and Distributions 9: 1 -8.
Brown and Litvaitis. 1995. Canadian Journal of Zoology 73: 1005 -1011
Implications of Changes in Scale Insects sampled at 10 -m intervals for 100 m
Implications of Changes in Scale Insects sampled at 2000 -m intervals for 20, 000 m
Landscape Processes • Landscape structure influences processes such as the flow of energy, materials, and species between the ecosystem within a landscape.
Landscape Structure and Dispersal of Small Mammals
Habitat Patch Size and Isolation and Density of Butterfly Populations
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.
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
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 Skip processes.
Introduction – Geographical Ecology • Mac. Arthur 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.
Oceanic Island = Terrestrial Island ? ? ?
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
Island Area and Species Richness
Species-Area Relationship S = c. Az S = # of species A = island area • Positive correlation between island size & number of species • Applies to terrestrial “islands” also
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
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
Lakes as Islands Skip
Marine Islands • Mac. Arthur and Wilson found isolation reduces bird diversity on Pacific Islands. • Williamson summarized data from relationship between island area and species richness in Azore Islands: – Birds show clear influence of isolation on diversity, ferns do not. – Land birds fly across water barriers, and ferns produce large quantities of light spores easily Skip dispersed in the wind.
Marine Islands Skip
Isolation and Habitat Islands on Continents • Lomolino et. al. found a strong negative relationship between isolation and the number of montane mammal species living on mountaintops across the American Southwest. Skip
Equilibrium Model of Island Biogeography • Mac. Arthur and Wilson: Model explaining patterns of species diversity on islands as result of immigration and extinction rates. – Reasoned rates of immigration would be highest on new island with no organisms. • As species began to accumulate, rate of immigration would decline since fewer arrivals would be new species.
Equilibrium Model of Island Biogeography • Predicted rate of extinction would rise with increasing number of species on an island for three reasons: – Presence of more species creates a larger pool of potential extinctions. – As number of species increases, population size of each must diminish. – As number of species increases, potential for competitive interactions between species will increase.
Equilibrium Model of Island Biogeography • Point where two lines cross predicts the number of species that will occur on an island. • Proposed rates of extinction on islands would be determined mainly by island size. – LG near islands will support highest number. – SM far islands will support lowest number. – SM near and LG far will support intermediate number. Skip
Island Biogeography • equilibrium model suggesting that the number of species occurring on an island represents a balance between immigration (in) and extinction (out) • Robert Mac. Arthur & E. O. Wilson
Experimental Island Biogeography • Simberloff and Wilson studied insect recolonization in Florida Keys. – Chose 2 stands of mangroves as control islands, and 6 others as experimental islands. • Defaunated islands – Followed recolonization for 1 yr. » Species number stayed constant, but composition changed considerably. Skip
Experimental Island Biogeography Skip
Colonization of New Islands by Plants • Rydin and Borgegard found variation in spp. richness correlated positively with island area and accounted for 44 -85% of variation in species richness among islands. – Small and medium islands continued to accumulate species. – Large islands attained equilibrium of immigration and extinction. Skip • Difficult to separate effects of habitat diversity from area effects.
Manipulating Island Area • Simberloff tested effect of island area on species richness. – In all cases where area was reduced, species richness decreased. • Richness on control island increased slightly. – Islands with reduced area lost species with each reduction in area. • Showed area has positive influence on species richness. Skip
Manipulating Island Area Skip
Island Biogeography Update • Brown and Kodric-Brown found higher immigration rates to near islands can reduce extinction rates. • Lomolino found island area can have a significant effect on immigration rates. • Area and isolation are only two of several environmental factors affect island species richness. Skip
Latitudinal Gradients in Species Richness • Most groups of organisms are more species-rich in the tropics. • Brown grouped hypotheses into six categories: – Time Since Perturbation • More species in the tropics because tropics are older and disturbed less frequently. – More time for speciation, and less frequent disturbance reduces extinction rate. Skip
Latitudinal Gradients in Species Richness – Productivity • High productivity contributes to high species richness. – More energy to divide among population. – Environmental Heterogeneity • More heterogeneity, thus more potential habitat areas and niches. Skip
Latitudinal Gradients in Species Richness – Favorableness • Tropics have more favorable environments. – No extremes to limit diversity. – Niche Breadth and Interspecific Interactions • Various themes – Brown suggests biological processes must play secondary role. » Ultimate causes must by physical differences. Skip
Area and Latitudinal Gradients in Species Richness • Rosenzweig proposed immigration can be largely discounted at broad scales, thus speciation will be primary source of new species. – Species removal via extinction. • Tropics richness is greater due to higher rates of speciation and / or lower rates of extinction. Skip
Continental Area and Species Richness • Rosenzweig found a strong positive relationship between area and species diversity. Skip