BIOL 3500Ecology

1
Lecture 15

• BIOL 3500Ecology
• Chapter 17 Processes Shaping Communities

2
Learning Objectives

• Contrast
• Fundamental vs. realized niches
• Direct vs. Indirect interactions
• Define
• Ecological niche
• Diffuse interaction

3
Two Niche Definitions

• Charles Elton (1930s) analogous to a job or
  trade in human society
• Old fashioned, but popular
• G. Evelyn Hutchinson (1957) the set of
  conditions and resources an organism requires
• More modern, this is accepted by most ecologists

4
Niche Dimensions

• Can be 1 dimension or several (n)

5
Barnacles Partition Niches

• All barnacles need space on a rock
• Some take higher position
• Some take lower position

6
Joseph Connells Study

• Intertidal zone in Scotland, 1960s
• Barnacles compete for space on rocks
• Two genera of barnacles

7
Connells Study (Contd)

• Balanus
• Superior competitor
• Will outcompete, crush other barnacles every time
• Chthamalus
• Loses to Balanus, if its present
• Superior at resisting dessication
• Can live high on rock, where Balanus cant

8
Fundamental Niche

• Set of resources conditions used by a species
• In isolation (no competition)
• Ideal circumstances

9
Realized Niche

• Set of resources conditions used by a species
• In competition, with other species present
• Never broader than fundamental niche
• Usually narrower

10
Barnacles

• Cthamalus
• Fundamental niche was broad
• Realized niche was limited by competition
• Balanus
• Fundamental niche and realized niches about the
  same
• Competition didnt matter

11
Community and Niches

• Community depends upon realized niches for
  individual species
• This gradient might represent moisture

12
Species Interactions are Diffuse

• Few communities are as simple as barnacles on a
  rock
• Charles Krebs of U of BC studied boreal forest
• 12 species eat snowshoe hares

13
Some Interactions are Indirect

• How does lynx population affect white spruce?

14
Keystone Species

• Remember some predators have very strong effect
  on their community
• Robert Paine _at_ U of Washington
• Removed Pisaster starfish from some areas, left
  other areas as controls
• Prey species dropped from 15 to 8
• Pisaster indirectly benefits some species

15
7th Inning Stretch
16
What are Daphnia?

• Important microcrustaceans in many ponds
• Frequently studied by aquatic ecologists
• Bioclassics website
• Nikon website

17
Midge/Salamander Indirect Mutualism

• Stanley Dodson (U of Wisconsin)
• Colorado ponds lacking salamanders, will also
  lack midges!
• Salamanders indirectly benefit Daphnia rosea
  their midge predators

18
Simplification of Food Webs

• Simplifying a food web into a food chain, a basic
  question arises
• Which is stronger in the community producers or
  consumers?

19
Hairston, Smith, Slobodkin (1960)

• Wrote important paper on food webs
• The American Naturalist, Vol. 94, No. 879
• Felt that resource-limitation was most important
• Coined the world is green hypothesis
• Now called HSS theory

20
HSS Theory Explained

• Imagine a one-level ecosystem
• Producers are limited by nutrients
• Now, a two-level system
• Producers released from competition, but
  herbivores now limited
• Then, a three-level system
• Herbivores released from competition, and
  carnivores now resource limited

21
Mary Power et al. (1985)

• Did experimental study of streams in midwest
• Ecology, Vol. 66, No. 5
• Counted algae, bass, minnows
• Experimentally manipulated presence of bass
• Where bass absent, very few algae
• Minnows became food-limited
• Where bass present, algae flourished