R. W. Baird

Predator (usually silent)

Familiar non-predator (frequently vocal)

Unfamiliar non-predator (frequently vocal)

Orcinus orca calls

K. Starks

Nature 2002

Phoca vitulina response (most common prey)

Changes in number of seals visible at the

surface

Distance of nearest seal to playback

source

Predation. One species benefits, the other incurs a cost; also herbivory & parasitism. Important in adaptive evolution: predator and prey adaptations.

Also important in shaping communities.

Plant defenses against herbivory.

pages 1178-1179

Mutualism. Both species benefit from the interaction. Some are obligatory: both species cannot persist without the other; others are facultative: the association is nonessential. Overlooked as a mechanism in community structure; it may be more significant than either competition or predation.

pages 1180-1181

Science 2003

F M

InflorescenceDominica

Flower

Bill

H. bihai H. caribaea

InflorescenceSt. Lucia

H. bihai H. bihai H. caribaea

H. bihai H. caribaea H. caribaea

Also important in adaptive evolution

1- When determining human population growth, do the only consider natural death or all causes?

SOME questions from February 17th

2- In the barnacle example, are you saying that Balanus is better suited to the environment and that if desiccation was not a problem at the higher water level, they would force out the Chthamalus?3- Assuming two species occupy the same ecological niche, why couldn’t they both co-exist assuming they were equally fit?

COMMUNITY STRUCTURE

Species InteractionsCompetition, Predation, Mutualism, Commensalism

Trophic StructureDominant and Keystone Species

Community Control

[Coevolution: reciprocal evolutionary change in interacting species, ending in some degree of specialization.]

TROPHIC STRUCTURE Feeding relationships between organisms. Describe species interactions.

Food chain- Transfer of food energy all the way until decomposers.

Trophic levels- Links in the food chain. Usually four or five.

Food web- Branching and interconnected food chains.

Fig. 53.10page 1181

ANTARCTIC FOOD WEB

Fig. 53.11page 1182

Fish

Zooplankton

Phytoplankton Proc. Natl. Acad. Sci. 18 Feb 2003

FOOD WEB TUESDAY LAKE, MI

Energetic hypothesis. Inefficiency of energy transfer along the chain limits the number of levels.

What limits the length of a food chain?

Dynamic stability hypothesis. Long food chains are less stable than short food chains.

Productivity in holes on tree trunks

Fig. 53.13

page 1183

Dominant species. Have the highest abundance or highest biomass (sum weight of all individuals).

treeguide.com

For example, sugar maple and impact on shading and soil and thus forest community.

Species that control community structure

pages 1183-1184

Exert control over the distribution and abundance of other species.

Keystone species. Exert strong control on community structure by their ecological roles (niches). They are not particularly abundant.

pages 1184-1185

For example, Pisaster ochraceous (ochre sea star) and Mytilus californianus (mussel).

Fig. 53.14

Keystone in wave-exposed sites, not so in wave-protected sites due to low food supply and sand burial.

Top-down model of regulation of community structure

western Alaska Science 1998pages 1185-1186

Examples of changes in community

structure regulated by predators

Bioscience 2005

Bottom-up model of regulation of community structure

Mar. Ecol.Prog. Ser. 2005

pages 1185-1186

Oikos 2004

Disturbance- Data suggest that the norm for most communities IS disturbance and nonequilibrium (constantly changing), rather than stability and equilibrium (species composition relatively constant).

Disturbances are events that damage communities, remove species and alter resource availability.

pages 1186-1188 Fig. 53.17

Despite the importance of natural disturbances, humans are the greatest agents of disturbance.

Mount St. Helens

19801978

1981 1999

ÙSFS

Ecological succession- Transitions in species composition over ecological time.

Primary succession- Begins in a virtually lifeless area where soil has yet not formed (new volcanic island or rubble left by retreating glaciers).

Secondary succession- Occurs where an existing community has been cleared by some disturbance that leaves the soil intact.

Glacier Bay, Alaska

Alder, cottonwoods: 30-80 yrs.

Spruce butting in: 80-200 yrs.

Spruce and hemlock: 200-300 yrs.

Secondary succession- Occurs where an existing community has been cleared by some disturbance that leaves the soil intact.

Yellowstone One year later