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

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 Science 2003 F M Inflorescence Dominica Flower Bill H. bihaiH. caribaea Inflorescence St. Lucia H. bihai H. caribaea H. bihai 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 Interactions Competition, Predation, Mutualism, Commensalism Trophic Structure Dominant 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 page 1181

ANTARCTIC FOOD WEB Fig page 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 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 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 For example, Pisaster ochraceous (ochre sea star) and Mytilus californianus (mussel). Fig 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 1998 pages

Examples of changes in community structure regulated by predators Bioscience 2005

Bottom-up model of regulation of community structure Mar. Ecol. Prog. Ser pages

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 Fig

Despite the importance of natural disturbances, humans are the greatest agents of disturbance. Mount St. Helens 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: yrs. Spruce butting in: yrs. Spruce and hemlock: yrs.

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