Parasite Box Model Example

• Brucellosis (undulant fever) is a bacterial disease of ruminant mammals and sometimes of humans. In ruminants, brucellosis causes a decrease in milk production, and can cause cows to abort their calves. It has been in the news because of concern that brucellosis infected bison in Yellowstone National Park may be able to spread the disease to cattle. Construct a box model and then write equations that show how brucellosis affects a population of bison. Once an animal is infected with brucellosis, it will carry the disease for the rest of its life. There is vertical transmission of the disease from mothers to offspring. In your box models and equations you should account for: x - the # of uninfected susceptible bison, y - the # of infected bison, a - per capita host birth rate for uninfected offspring, b - natural, non-disease mortality rate, alpha α - disease induced mortality rate, beta β - transmission coefficient, and zeta ζ - birth rate of infected young.

Symbioses - Mutualism

Endosymbiotic Origin of Eukaryotes

Lynn Margulis

Endosymbiotic Origin of Eukaryotes

Endosymbiotic Origin of Eukaryotes

• The earliest eukaryotes acquired mitochondria by engulfing alpha proteobacteria.

• The early origin of mitochondria is supported by the fact that all eukaryotes studied so far either have mitochondria or had them in the past. Mitochondria have their own DNA and replicate themselves during cell division.

• Later in eukaryotic history, some lineages of heterotrophic eukaryotes acquired an additional endosymbiont—a photosynthetic cyanobacterium—that evolved into plastids.

• This hypothesis is supported by the observation that the DNA of plastids in red and green algae closely resembles the DNA of cyanobacteria.

• Plastids in these algae are surrounded by two membranes, presumably derived from the cell membranes of host and endosymbiont.

Stromatolites on coast of Western Australia

The Nature of Communities and Ecosystems

Sourdough bread – ingredients and final product

Redwood Forest

Scale of Ecosystem – Lake Superior

Scale of Ecosystem – Isle Royale

Scale of Ecosystem – Isle Royale – Forest and Pond

Scale of Ecosystem – Isle Royale Wetland

Scale of Ecosystem – Isle Royale Pitcher Plants

Ecotone – region where two communities/ecosystems grade into each other

Forest-Marsh Ecotone

Stability

A stable community or ecosystem is one that has the ability to replace

itself – exist in place for more than one generation

Douglas-Fir

Pea Aphids

Life cycle of the Pea Aphid

Components of Stability

2 major components:

1) resistance - the ability of a community or ecosystem to avoid disturbance - how most people think of stability

2) resilience - the speed with which a community or ecosystem returns to its former state following a disturbance that has displaced it from its initial condition

Ecosystems and Stability

Grassland – South Africa Rainforest – Puerto Rico

Additional Components of Stability

• Local stability describes the tendency of a community to return to its original state following a small disturbance

• Global stability describes the tendency of a community to return to its original state following a large disturbance

Adaptive Capacity of an Ecosystem

Adaptive Capacity of an Ecosystem

Adaptive Capacity of an Ecosystem- Chesapeake Bay

Adaptive Capacity in 3D

Current Adaptive Capacity

From Local vs. Global Stability

• dynamically fragile - a community which is stable only within a narrow range of environmental conditions

• dynamically robust - a community which is stable within a wide range of environmental conditions

Complexity and Stability

Current understanding - no clear relation between complexity and stability

1) complex, fragile communities of relatively constant environments (the tropical rainforests) are more susceptible to outside, unnatural disturbances than are simpler, more robust communities which experience regular climatic fluctuations (most temperate communities)

2) In stable environments you would expect to find K selected species (high competitive ability, high survivorship, low reproductive output) and such species will resist disturbance

3) In unstable environments you would expect to find r selected species (low competitive ability, low survivorship, but high reproductive output) that have little resistance but high resilience

Aerial viewOf 1989Yellowstone Fire

Why is the World Green?

Boreal Forest Outlined in Green

Spiny Water Flea

Spiny Water Flea Invasion

MaryPower

Eel River with steelhead Eel River without steelhead