Ecological succession describes the predictable changes in communities over time. Primary succession occurs on new surfaces without soil, while secondary succession follows a disturbance with existing soil. Succession proceeds through stages from pioneer species to a climax community. Invasive species can disrupt normal succession. Community interactions include predation, competition, mutualism, commensalism, and parasitism. Early successional communities have simpler structures and functions than late successional communities.

1. Ecological Succession &
Community Interactions

2. Succession
 A series of regular, predictable, quantifiable
changes through which ecological
communities go through.
• Primary succession: “Pioneer species”
colonize a newly exposed area (lava flows,
glacial retreat, dried lake bed). No soil!
• Secondary succession: The community
changes following a disturbance (fire,
hurricane, logging). Soil present.

3. Primar y terrestrial
succession
1. 2. 3. 4. 5. Climax
Figure 5.24

4. Primar y aquatic
succession
 1. Open water
 2. Pioneer Plants
begin to cover water
surface; sediment
deposited
 3. Pond filled by
sediment; vegetation
grows over site
Figure 5.24

5. Secondar y terrestrial
succession
1. 2. 3. 4. Climax
Figure 5.23

6. Climax Community
A stable group of plants and
animals that is the end result
of ecological succession
Does not necessarily mean
huge trees. In prairies and salt
marshes the dominant plants
are grasses -- and in deserts
the dominant vegetation are
cacti.

7. Ecosystem Characteristics at Immature and Mature Stages of Ecological Succession
Immature Ecosystem Immature Ecosystem
Characteristic (Early Successional Stage) (Late Successional Stage)
Ecosystem Structure
Small Large
Plant size
Low High
Species diversity
Mostly producers, few decomposers Mixture of producers, consumers,
Trophic structure
and decomposers
Few, mostly generalized
Ecological niches Many, mostly specialized
Low
Community organization High
(number of interconnecting
links)
Ecosystem Function
Low High
Biomass
High Low
Net primary productivity
Simple, mostly plant herbivore Complex, dominated by
Food chains and webs
with few decomposers decomposers
Efficiency of nutrient recycling Low High
Efficiency of energy use Low High
Table

8. Invasive species
 A species that spreads widely and rapidly
becomes dominant in a community, changing
the community’s normal succession
 Many invasive species
are non-native, introduced
from other areas.
 Purple loosestrife invades
a wetland.
Figure 5.25

9. Community

Interactions
The relationship between the different
populations of organisms in a geographical
area.
 Some relationships are
symbiotic (close, long-
term interaction).
 Some relationships are
harmful to a population
or species, some are
beneficial.
Figure 5.25

10. Predation
 One species, the predator, hunts, kills, and
consumes the other, its prey.
Example:
Snake
captures
and eats a
frog
Figure 5.16

11. Predation drives adaptations
in prey
Cryptic coloration: Warning Mimicry:
Camouflage to hide coloration: Fool
from predators Bright colors warn predators
that prey is toxic (here,
caterpillar
mimics Figure 5.18

12. Competition
 When multiple species
seek the same limited
resource
Interspecific competition is
between two or more species.
Intraspecific competition is
within a species.
 Often does not involve
active fighting, but subtle
contests to procure
resources.

13. Mutualism
Symbiotic relationship in which both
species benefit one another.
Example:
Hummingbird
pollinates
flower while
gaining nectar
for itself.
Figure 5.22

14. Mutualism
Examples
Oxpeckers and black rhinoceros Clown fish and sea anemone
Mycorrhizae fungi on juniper Lack of mycorrhizae fungi on
seedlings in normal soil juniper seedlings in sterilized soil

15. Commensalism
Symbiotic relationship in which one species
benefits and the other is unaffected.
Example: Cattle
egrets feast on
insects that are
aroused into flight by
cattle grazing in the
insects' habitat. The
Cattle does not
benefit at all
Figure 5.22

16. Parasitism
Symbiotic relationship in which one species,
the parasite, exploits the other species, the
host, gaining benefits and doing harm.
Example: Tick
feeding on blood and
transmitting disease
Figure 5.21