Communities and Biodiversity Lecture 14 Chapters in Text: 18, 19 Ecosystem structure and stability C

1
Communities and BiodiversityLecture 14 Chapters
in Text 18, 19Ecosystem structure and
stabilityCommunity Succession
2

• California Floristic Province
• Many Rare and Endangered Species
• Giant Sequoia
• Giant Kangaroo Rat
• California Condor
• Overview
• Wide variety of habitats
• sagebrush steppe, prickly pear shrubland, coastal
  sage scrub, chaparral, juniper-pine woodland,
  upper montane-subalpine forest, alpine forest,
  riparian forest, cypress forests, mixed evergreen
  forests, Douglas fir forests, sequoia forests,
  redwood forests, coastal dunes, and salt marshes

3
California Floristic Province
4

• Community Diversity or Biological Diversity
• Two components
• Species richness
• Describes number of species present
• Relative abundance
• Percentage each species contributes to total
  species composition
• Measure of Species Evenness

5

• Quantification and Comparison of Diversity
• Simpsons Index D
• several forms are used
• Probability that 2 random samples will be of same
  species from a sample of a community
• Value 0?1 where 1 same species (no diversity)
• Smaller value of D corresponds with greater
  diversity
• D S(n1/N)2

Number individuals of species 1
Total Individuals all species
Summation for all species
6

• Rank Abundance Curve
• Visualization of relative abundance of species in
  different habitats

Steep slope suggest relatively fewer species than
deciduous forest
7

• Food Web
• Represent various species interactions
• Trophic (feeding) levels provides functional
  classification
• Basal Species feed on none, are fed upon
• Intermediate
• Top predators
• Guilds
• Divisions of trophic level
• Species which exploit similar resources in
  similar fashion
• Community as complex assembly of guilds
• May be only distantly related

8
http//faculty.mccfl.edu/rizkf/OCE1001/Images/food
web.jpg
9

• Functional Groups w/i Communities
• Based on niche aspects
• Conditions as Shade tolerant, drought addapted
• C3, C4, CAM photosynthetic
• Nature of reproductive cycles
• Interoparous
• Selemparous
• Annual/perennial

10

• Dominant Species
• Single or few species which are predominant in a
  habitat
• Generally defined for a group ie. Tree, grass,
  shrub, etc.
• Factors other than numbers may define dominance
• Size (biomass) may be defining factor

11
(No Transcript)
12

• Food Web Stability
• Consistency resistance to change imposed by
  outside factors
• Resilience ability to return to reference state
  after disturbance
• Example grassland Ecosystem Change with
  increased precipitation
• Immediate productivity gain
• Long-term effect
• Returns to original productivity level
• Species composition changes
• New altered steady-state

13

• Steady States
• Status about which a community functions
• Variations due to minor perturbations
• More than one
• Established with major outside change
• Climatic change
• Removal of major prey item
• Introduction of major/keystone predator
• Example prairie plant community enforced by fire
• Removal of fire ?
• Introduction of new grazers ? ?

14

• Views of Community Structure
• Holistic concept ? Closed community
• Clements community structure determined by
  vegetation
• Organisms considered in relation to their role
  (niche)
• Associations are a consequence of evolutionary
  processes
• Individualistic concept ? Open community
• Gleason associations are a coincidence
• Community functions as a result of sum of
  individual actions

15

• Closed community
• Species occur in unique, associated sets
• Discrete boundaries little overlap
  distribution spatially determinant
• Open community
• Community members may occur in various
  associations
• Indeterminate spatial distribution
• Ecotone area of transition spp at edge of
  distribuiton

16
(No Transcript)
17

• Continuum concept - Whittaker
• Species distributed along environmental gradient
• Gradient analysis abundance of species plotted
  against 1 env. condit
• Examples
• Mountain slope
• Gradients of temperature and precipitation
• Eastern Hardwood Forest
• North south gradient temperature
• East-west precipitation

18
(No Transcript)
19

• Disturbance an event that changes a community
• Primary succession
• Occurs where no soil exists when succession
  begins
• Rare usually soil is present!
• The first plants to appear from a pioneering
  community
• Secondary succession
• Begins in an area where soil remains after a
  disturbance
• Passes through phases, each known as a sere
• Each sere and the ultimate climax community
  varies with physical conditions

20

• Old Field Succession Dwight Billings
• Early species to invade weedy or r-selected
  species
• Do not compete well for resources, high
  reproductive rate
• Shift to k-selected species
• Changes in nature of habitat favor species which
  reproduce successfully at or near carrying
  capacity

21
(No Transcript)
22

• Early Stages of Old Field Succession
• Pioneer Species tolerant of soils with
• Low nutrient/humus availability
• Low water holding capacity
• High temperature flux
• Annuals ? biennials
• Add organic matter

23

• Later Stages in Old Field Succession
• Invasion by perennials shrubs and trees
• Increasing levels of soil organic matter
• Water retaining capacity
• Deeper root systems of perennials tap water and
  nutrients at greater soil depths
• Increasing competition for sunlight
• Forest development Early species soft woods
  (largely rapidly growing conifers)
• Creation of microclimate
• Shift to slower growing hardwoods Shade
  tolerant species

24

• Climax Ecosystem?
• Communities are in constant flux
• Tends to convey idea of stasis, rigid
  successional sequence
• Succession leads to Mature Ecosystem
• Successional events slow
• Modification of community structure still happens
  - Nonequilibrium model
• Moderate disturbance
• Climatic changes
• Disease pressure
• Communities are constantly changing as they are
  buffeted by disturbances

25

• Smoky Bear A Dangerous Reactionary?
• Fire as an important force in maintenance of
  ecosystem vitality
• Is a significant disturbance in most terrestrial
  ecosystems
• Is often a necessity in some communities

26

• Fire suppression
• Nutrients tied up in dead material
• Hotter fires, considerably more damage
• Fire Ecology
• Heat of fire
• Time since last burn
• Succession
• Fire followers
• Smoke induces germination
• Frequency of fire

27
(No Transcript)