1. BIOL 4120: Principles of Ecology Lecture 17: Community Ecology
Dafeng Hui
Room: Harned Hall 320
Phone:

2. Outline (Chapter 18) Community dynamics
18.1 Community structure changes through time
18.2 Primary succession occurs on newly exposed substrates
18.3 Secondary succession occurs after disturbances
18.4 Study of succession has a rich history
18.5 Succession is associated with autogenic changes
18.6 Species diversity changes during succession
18.7 Succession involves heterotrophic species
18.8 Systematic changes occur as a result of allogenic changes
18.9 Concept of community revisited
Spatial distribution of species and factors influence community structure on the landscape. Zonation (changing of community structure across the landscape) reflects the shifting distribution of populations in response to changing in environmental conditions as well as the interactions among species (direct and indirect).
Next, how community structure changes with time? Community dynamics

3. 18.1 Community structure changes through time
Successional changes over 30 years in a western Pennsylvania field.
Cropland or Grazed grassland  grasses, goldenrod, weedy herbaceous plants  shrubs (blackberry, hawthorn) fire cherry, pine, aspen  forest of maple, oak, cherry or pine.
Chapter 13:

4. Succession
Definition: The process of gradual and seemingly directional change in the structural of the community through time fro field to forest
Temporal change in community structure
Sere (from the word series): sequence of communities from grass to shrub to forest historically
Seral stage: a point of continuum of vegetation through time
can be short or long (1 or 2 yrs to several decades)
Succession happens in both terrestrial and aquatic environments

5. William Sousa
Process of succession in a rocky intertidal algal community in southern California
Use concrete blocks for algae to colonize
Panel b shows succession
Early successional species (pioneer species):
High growth rate, small size, high degree of dispersal, high rates of population growth
Late successional species:
Low rate of dispersal, slower growth rate, larger and live longer.
Species dominance change along time

6. Hubbard Brook Experimental Forest, New Hampshire
Process of succession after forest clearing
Prior to clearing, beech and sugar maple seedling dominate understory
Following clearing, pin cherry, yellow birch etc.; will be replaced by of beech and maple later
Primary succession (example before) and
secondary succession (this example)
Species dominance change along time

7. 18.2 Primary succession occurs on newly exposed substrates
Primary succession begins on sites that never have supported a community, such as rock outcrops and cliffs, sand dunes, and newly exposed glacial till.
Primary succession on a coastal sand dune colonized by beach grass
Later on, shrub, then trees (pines and oak)
Chapter 13:

8. Glacier Bay fjord complex in southeastern Alaska
Glacier Bay fjord complex in southeastern Alaska. Ice retreats, primary succession occurs

9. 18.2 Secondary succession occurs after disturbances
Terrestrial environment:
Old field succession in the Piedmont region of North Carolina by Dwight Billings in the late 1930s
Abandoned farmland
Decline in pine and increase in hardwood (oak and hickory)
Chapter 13:

10. 18.3 Rich history of succession study
Friderick Clements (1916, 1936): Monoclimax hypothesis
view community as a highly integrated superorganism, the process of succession represents gradual and progressive development of community to ultimate or climax stage (similar as development of an individual organism)
F. Egler (1954):Initial floristic composition
succession at any site depends on which species gets there first. No species is competitively superior to another. Once the original dies, the site becomes available to others.
Joesph Connell (1977): three models (facilitation model, inhibittion model, and tolerance model)
Overall: adaptations and life history traits of individual species influence species interactions and ultimately species distribution and abundance under changing environmental condisiotns.
Chapter 13:

11. 18.4 Succession is associated with autogenic changes in environmental conditions
Environmental changes can be grouped into two classes:
Autogenic (direct result of organisms within community)
Created by community itself
Light in a forest
Allogenic (a feature of physical environment)
Created by physical environment
Elevation on a mountain
Stress in a salt marsh
Succession: changes in community structure through time; specifically, changes in species dominance)
When plant succession, it creates autogenic environmental change in a place
Both primary and secondary succession, colonization alters environmental conditions
Chapter 13:

12. Light availability decline from canopy to ground levels
When plant succession, it creates autogenic environmental change in a place. For example, light environment (vertical distribution)
Light availability decline from canopy to ground levels
Initial colonization, the light at ground level is high, seedlings are able to establish themselves.
As plants grow, their leaves intercept sunlight, reducing light to short plants
The reduction in light enables fast-growing plants to out-compete the other species and dominate the site
Sun-adapter, share-intolerant plants exhibit high rates of photosynthesis and growth under high-light conditions. Under low light, they can not survive
Shade-tolerant species exhibit much low photosynthesis rate and growth under high-light conditions, but are able to continue photosynthesis and growth, and survival under low-light (trade-off)
In the early stage, shade-intolerant species dominate because of their high growth rate. They grow and shade the slower growing, shade-tolerant species. As time progresses and light level decline below the canopy, seedlings of the shade-intolerant species can’t grow and survive in the shaded conditions. At this time, although shade-intolerant species dominate the canopy, no new individual are being recruited. In contrast, shade-tolerant species will germinate and grow, and replace the old, dead shade-intolerant spp.
Chapter 13:

13. Shade intolerant die out due to no seedlings Shade tolerant take over
Example of succession
1st
Shade intolerant species
Eventually dominate only in canopy
2nd
Shade tolerant species invade
Shade intolerant die out due to no seedlings
Shade tolerant take over

14. 18.6 Species diversity change during succession
In addition to shifts in species dominance, patterns of plant species diversity change over the course of succession.
Comparison of species diversity at different sites within an area that are at different stages of succession
Chronosequences (or chronoseres)
These groups of sites
For example, farmland abandoned at different times
Chapter 13:

15. Changes in plant diversity during secondary succession of an oak-pine forest in Brookhaven, New York.
Species richness increases into the late herbaceous stage, declines into the shrub stage, then increases in the early forest stages, then decreases thereafter.

16. Normal growth rate
Double growth rate
Hypothetical succession involving five plant species
Species diversity increases initially as new species colonize the site. As autogeneically changing environments and competition result in the displacement of early successional species, diversity declines

17. Pattern of succession under three different disturbance frequencies
Wrong?
Intermediate disturbance hypothesis: community with intermediate disturbance has large species diversity

18. 18.7 Succession involves heterotrophic species
Not only autotrophic component of community (plant succession) show succession, changes in heterotrophic component of the community also occur.
Decomposition
Tree fall  bark beetle, wood boring beetle  fungi  bacteria  predator insects (centipedes, mites, pseudoscorpions, beetles)  fungi  moss and lichens  seedlings
Chapter 13:

19. As plant succession advances, changes in structure and composition of the vegetation result in changes in the animals life that depends on vegetation as habitats.

20. 18.8 Systematic changes in community structure occur as a result of allogeneic environmental change at a variety of timescales
Shifting patterns of community structure in response to autogenic environmental changes often occur at time scales relating to the establishment and growth of the vegetation.
Purely abiotic environmental change can produce patterns of succession over time scales ranging from days to millennia.
Chapter 13:

21. Paleoecology: study of distribution and abundance of ancient organisms and their relationship to the environment
Chapter 13:

24. 18.10 The concept of community revisited
Two views of community: organismal view and individualistic view
Reality lies somewhere in the middle
Organismal community is a spatial concept: variety of plant and animal species interacting and influencing the overall structure
Continuum view is a population concept, focusing on the response of the component species to the underlying features of the environment.
An example (demonstrate two views)
Chapter 13:

25. One view: species distributions are plotted as a function of altitude or elevation. 4 species exhibit a continuum of species regularly replacing eath other in a sequence of A, B, C and D with increasing altitude.
Another view: species distribution is a function of distance along the altidinal gradient. As we move up the mountain, the distribution of 4 species are not continuous. A number of associations are recognized as we walk along the transect.
Two views are quite different yet consistent. Each species has acontinuous response along an environmental gradient. Yet it is the spatial distribution of that environmental variable across the landscape that determine the overlapping patterns of species distribution.
Patterns of co-occurrence for 4 plant species on a landscape along a gradient of altitude

26. Same approach can be applied to patterns of forest communities in the Great Smoky Mountain National Park.
(b) associations, support the first view, Clements’s view.
(c) Species appears to be distributed independent of each other, supporting Gleason’s view.

27. End

28. Changes in diversity in one part of community can affect another part
Greater diversity of vertical layers of forest
More bird species
Variation in diversity during forest succession
Affects mammal species