succession and stability (ch. 20). community/ecosystem “stability” stability: absence change...

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)!