succession and stability (ch. 20). community/ecosystem “stability” stability: absence change...
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Succession and Stability (Ch. 20)
Community/Ecosystem “Stability”
• Stability: Absence change
• Resistance: Maintain structure/function in face of disturbance/stress
• Resilience: Speedy recovery
Desert Stream “Stability”• Surface/subsurface waters: Sycamore Creek AZ.
– Upwelling: from streambed to surface– Downwelling: opposite– Upwelling zones high nitrate
Desert Stream “Stability”• Upwelling zones rapid recovery after flood
(great resilience)
Desert Stream “Stability”• Resistance: Maintain structure/function in face
of disturbance.– Upwelling zones determined by bedrock– Not influenced floods: resistant to flood effects
Studying succession: repeat photography
• Recall chronosequence: sites vary in time since disturbance
• Can study succession same site: using repeat photography– Ex, MacDougal Crater, Mexico
Volcanic crater1 mile diameter
• 1907
• 1959
• 1972
• 1984
• Changes:
Fewer cresosote bushes, more saguaro
• Photo points: being established in parks
Enchanted Mesa,New Mexico.Juniper more common
LandscapeEcology Ch. 21
Landscapes• Landscape Ecology: Study landscape structure &
processes– Landscape: Heterogeneous area (several ecosystems)– Landscape Elements: Visually distinctive patches in
ecosystem
Landscape Structure• Ex: analysis Ohio landscapes
– Compare Monroe vs. Somerset (most? How much more?)
Landscape Structure• Ex: analysis Ohio landscapes
– Compare Monroe vs. Somerset– Which of 6 has most forest cover?
Landscape Structure
Patch no.? Size? Shape?
Landscape Structure• Quantify patch shape: patch perimeter divided
by perimeter circle w/area = patch
S = P/2(A)– S = Patch shape
• Increasing value indicates less circular shape
– P = Patch perimeter– A = Patch area
Landscape Structure• Perimeter/area relations can matter….
• Edge effect: altered habitat at fragment margin– Ex, forest patches--Major impacts:
• Increased % edge habitat (ecotone)
• Decreased distance edge to center
– Effects differ on edge vs. interior species
Edge effects example
• Negative species interactions– Predators, nest parasites
Who am I?
Hint?
Edge effects• Ex, brown-headed cowbird
– Brood parasite: lays eggs nests >100 birds
– Studies: parasitism increases fragmented forests
Parasitized nest (2 cowbird eggs)
Fractal Geometry• Describe mathematically complex shapes
Fractal Geometry• Perimeter estimates depend on size
measuring device.
AK!
Fractal Geometry• Ex, Admiralty
Island, AK
Fractal Geometry• Coastline length differs: eagles and oil
molecules!
Exxon Valdez: 2,000 km coastpolluted (1989)
Landscape Processes• Landscape processes: energy, materials, species
move between ecosystems
• Metapopulations: Spatially isolated patches (significant exchange individuals)
Landscape Structure and Dispersal
• Ex: desert bighorn sheep
Landscape Structure and Dispersal
• Ex: desert bighorn sheep
Landscape Structure and Dispersal
• Ex: bighorn sheep
• Populations <50 extinct!
Landscape Structure and Dispersal
• Patch size affects movement
Sherman live trap
Landscape Structure and Dispersal• Results
Peromyscus(deer mouse)
Sigmodon(cotton rat) Small patches: animals move farther
Landscape Structure and Dispersal
• Fewer animals move in small patches (fragmentation leads to less moving)
Microtus(vole)
Landscape Structure and Dispersal
• Butterfly density affected by patch size & isolation
Melitaea cinxiaGlanville fritillary
Plantago lanceolataLarval food plant
Landscape Structure/Dispersal• Pop. size increased with patch area (1)• Pop. density decreased as area increased (2)
1
2
Landscape Structure/Dispersal• Other conclusions….Isolated patches have low
butterfly densities– Partially maintained by immigration– Small pops. likely go extinct!
Dispersal• So, populations can be:
• 1) source populations: supply immigrants
• 2) sink populations: require immigrants to persist
Habitat corridors• Connecting habitat
– Corridors influence movement butterflies
Common buckeye
Variegated fritillary
Habitat corridors
• Corridors (large scale)
• Ex, Cascades….
Habitat corridors• Corridors (small scale)
Landscape bridge overhighway in Germany
Landscape Position and Lake Chemistry
• Lake position affects responses to drought.
Landscape Position and Lake Chemistry
• Lower lake: level changed less• Dissolved minerals changed more
Soil/Vegetation Mosaics Sonoran Desert
• Bajadas (sloping eroded materials @ base mountains) in Sonoran Desert
Soil/Vegetation Sonoran Desert• Plant distributions: affected by soil age
– Old soils with caliche and clay
Caliche: Cemented carbonate layer
Soil/Vegetation Mosaics Sonoran Desert
• Soil structure
Larrea: dominates old + young soils
Ambrosia: dominates soils ofintermediate age
Organisms & Landscape Structure• Humans: conversion of forest to agricultural
landscapes.
Humans• Cadiz township, WI. Clearing for agriculture
(fragmentation)
Humans• Netherlands: forest increased as sheep raising
ceased
heathland US: sharecropping
Other Organisms and Landscape Structure
• African elephants & trees.– Change woodland to grassland.
Other Organisms and Landscape Structure
• Kangaroo Rat burrow systems
Aerial photo
Banner-tailed kangaroo rat
Other Organisms and Landscape Structure
• Alligator ponds (Everglades)
• Refuges: aquatic organisms during droughts
Other Organisms• Beavers modified nearly all streams
Other Organisms• Trapping (mostly fur) almost drove them
extinct
Organisms• Study: – Beavers changed boreal
forest to mosaic.
Organisms• Beavers (1927-1988) increased most ions and
nutrients
Last story….
Fire and Structure of a Mediterranean Landscape
• Chaparral (Mediterranean shrubland) in S. California. Burns periodically
Fire and Structure of a Mediterranean Landscape
• Fire suppression: Effect on fire size?
Fire and Structure of a Mediterranean Landscape
• Study: satellite photos
• Reconstruct fire history S. CA & N. Baja (1971-80).– Similar climates (little fire
suppression N. Baja)
2007 smoke plumes
Fire and Structure of a Mediterranean Landscape
• Total area burned similar
Fire and Structure of a Mediterranean Landscape
• Small burns frequent in N. Baja, larger burns S. CA
• Fire suppression leads to larger fires (megafires: very large & destructive)!