Slide deck from APES class on 11/13/12.

1. Population Changes in Context - in Communities!

2. Succession Defined:
• The gradual, sequential change in the relative
abundances of the dominant species in a
biological community following a
disturbance…
• Primary succession: beginning from an
abiotic environment following a cataclysmic
disturbance
• Secondary succession: beginning from a
major disturbance, but all forms of life are
not destroyed

3. Primary or Secondary?
Volcanic Island

4. Primary or Secondary?
1988 Fires in Yellowstone NP

5. Primary or Secondary?
Old Parking Lot

6. Primary or Secondary?
Glacial Retreat

7. Primary or Secondary?
Old Farm

8. Primary Succession (forest)
• Colonization: of bare rock, tiny seedless plants like
mosses, and lichens, “pioneer species”
• Early: plants typically small with short lifecycles
(annuals), rapid seed dispersal, “environmental
stabilizers”
• Middle: plants typically longer lived, slower seed
dispersal (herbs, shurbs, perennials)
• Late: plant species are those associated with older,
more mature ecosystem-largest vegetation (trees)
• “Climax Community” mature forest in this case
(but varies by biome)
*Note: Consumers and decomposer populations will also vary as
producer populations change…as well as nutrient cycling…

9. Research on Primary
Succession

11. Research on Secondary
Succession

12. Hutcheson Memorial Forest
Center (NJ)
Old Field Secondary Succession1962-1995

13. Hutcheson Memorial Forest
Center (NJ)
Old Field Secondary Succession1962-1995

14. Hutcheson Memorial Forest
Center (NJ)
First Year

15. Hutcheson Memorial Forest
Center (NJ)
Fifth Year

16. Hutcheson Memorial Forest
Center (NJ)
Tenth Year

17. Hutcheson Memorial Forest
Center (NJ)
Twentieth Year

18. Hutcheson Memorial Forest
Center (NJ)
Twenty-Eighth Year

19. Changes in Biodiversity

20. © 2003 John Wiley and Sons Publishers

21. © 2003 John Wiley and Sons Publishers

22. Succession in Aquatic
Ecosystems
© 2003 John Wiley and Sons Publishers

23. Succession in a Pond
1960s to 1990s

24. Is a Climax Community
Always Inevitable?
• New research suggests that we cannot
always project the course of a given
succession or view it as preordained
• Communities are always subject to
disturbances and we cannot always know
the outcome
• Disturbances can be beneficial for
communities…

25. The Intermediate
Disturbance Hypothesis
• Hypothesis: Communities that experience fairly
frequent but moderate disturbances have the
greatest species diversity
• Reasoning: Moderate disturbances are large
enough to create openings for colonizing species
in disturbed areas, but mild and infrequent enough
to allow the survival of some mature species in
undisturbed areas

26. ‘General Ecology’, D.T. Krohne

27. Ecotones
• Disturbances often create ecotones, but they also
exist as natural transitions between biomes or
ecosystems
• An ecotone is a transition area between two
adjacent ecological communities
– a sharp boundary or a gradual blending effect
– particularly significant for mobile animals, as they can
exploit more than one set of habitats within a short
distance
– this can produce an edge effect along the boundary
line, with the area possibly displaying a greater than
usual diversity of species

28. Edge Effects
• Disturbances can fragment ecosystems and create
edge effects
• An edge effect describes the differing abiotic and
biotic conditions that exist at a border between
contrasting environments in an ecosystem
– the increased light, greater wind and temperature
extremes and lower humidity at the boundaries of
fragments favor some plant species over others (native
colonizing species or invasive species)
– this can make the combination of species present near
the boundary different from that inside the fragment
(more diverse or less depending on the factors)

29. Remember This Edge Effect?
Kudzu at DCEP

30. The Island Theory of
Biogeography
• Small islands have fewer habitat types and greater
risk of extinction-smaller islands have less genetic
diversity too
• The more distant the island, the less chance of
reaching it
• Over time, an island tends to maintain a constant
number of species, because the rate at which
species are added is about the same as the rate at
which other species become extinct

31. The Island Theory of
Biogeography
• Species often evolve to a smaller size on islands
because islands often have a limited supply of
food, fewer predators, and fewer species
competing for the same resources
• Examples include island foxes, pygmy
mammoths, and a dwarf human species Homo
floresiensis

32. The Island Theory of
Biogeography
• Island concepts can also be applied to
“ecological islands”
• Ecological islands are comparatively small
habitats separated from a major habitat of
the same kind
– A small stand of trees within a prairie is a forest
island

33. Habitat Fragmentation (and
ecological islands)

34. Solution: Wildlife Corridors

35. Bibliography
• http://www.ecostudies.org/bss/index.html
• http://www.lifeinfreshwater.org.uk/Web%20pages/ponds/Succession%
20Intro.htm
• http://www.linc.us/FloridaWidlifeCorridor_Info.html