Food webs and trophic cascades
Intermediate disturbance hypothesis
Species area curves
Theory of island biogeography
food chain, food webs
A ___ depicts the linear sequence of who eats whom in a community.
Food chains are interconnected to make ___
Only 10 percent of energy of one trophic level is transferred to the next level:
-___: energy used for respiration and metabolism; dissipated as heat and lost to the community
-___: not all biomass can be ingested
-___: not all ingested biomass is usable
___ show energy, biomass or numbers of individuals at each trophic level.
Bottom right, why is there more biomass in primary consumers than producers. Phyloplankton have very fast turnover and primary consumers have very slow turnover, so their fast activity is able to energetically support a biomass much larger than them
Species interactions, especially antagonistic interactions, have a strong influence on an ecological community.
Interactions of one consumer species can cause a progression of indirect effects across successive trophic levels, or a ___
Strongest interactions in food webs are due to antagonistic interaction-basically predation
Trophic cascade example
In Yellowstone National Park, wolves were extirpated by hunting by 1926.
Elk were culled each year to prevent them from exceeding carrying capacity, until 1968. Elk population then rapidly increased.
The elk browsed aspen trees so heavily that young aspens could not get a start.
Elk also browsed streamside willows to the point that beavers (who depend on willows for food) were nearly exterminated.
Wolves were reintroduced in 1995, and preyed primarily on elk. Aspen and willow re-grew, and beaver population increased.
Wolves were extirpated by hunting by 1926.
Elk were culled each year to prevent them from exceeding carrying capacity, until 1968.
Elk population then rapidly increased.
Wolf on elk neg, elk on aspen neg. neg times neg=positive. Wolf has positive effect on aspen
Elk browsed aspen trees so heavily that young aspens could not get a start.
Wolves were reintroduced in 1995, preyed on elk, aspen re-grew.
Abiotic factors and recovery following a large-scale disturbance
A fire comes through and resets it, but not like a primary succession. These disturbances are similar to predators that reset, but on a different scale
Disturbances have a similar effect. Fires can be more frequent or not very common. Little fire, patch of land very old and there are few species that have a mature stand in the system. But at intermediate levels, disturbance takes out top competitors and other can come in. If it's very common, it kills off almost everything except those that are best equipped to survive. Depends on FREQUENCY
New Zealand disturbance example pic
In contrast to secondary succession, involves an event that opens up bare rock, a glacier or landslide for example.
Glacial retreat in southeastern Alaska and primary succession
primary succession example
The glacier moves, revealing new ground to be colonized. Set up study plots and look over short term what was going on. Swapped space for time and just looked up and down the path of the glacier saying that what was happening in 1941 was happened 200 yrs earlier further up the stream
4-stage explanation pic
You can see the transition of the species. Whats going on is that nitrogen fixation by dryus and alders that pave the way for spruce and others-facilitation
Effects of early successional species on later species
___: Species modify the environment so as to facilitate colonization by other species.
Example: The N-fixation by Dryas and alders that allows spruces to become established in Glacier Bay.
___: Species inhibit arrival of others. This effect lasts as long as early species persist.
Example: Old-field species such as goldenrod and thistle produce root exudates that inhibit the germination and growth of potential competitors.
Diversity has different components depending on the scale at which it is measured:
___: within a single community or habitat
___: between-habitat diversity; change in species composition from one community to another
___: regional diversity over a range of communities in a geographic region
High beta diversity, two separate circles. Low beta diversity, one circle within another. And anything in between, like a venn diagram
Two components of diversity.
"___" = number of species.
"___" = relative abundance.
Tropical richness in trees: example of alpha diversity
Number of species of trees in certain areas of the world. A measure of alpha diversity
Number of tree species in 50 hectare plots.
Counted all individuals > 1 cm in diameter
Biogeographic realms: example of gamma diversity
Laid out by wallace and found by darwin. Noted that in various regions of the world, there are groups of plants and animals that seem to be typical worldwide. These are gamma diversity issues
____-Tropics have many more species than more temperate regions. A lot of interest regarding what makes that
Eight hottest hotspots (all in the tropics)
All in tropics. Look at these, last column is primary vegetation remaining of original extent. Push to save the tropics. A concern of biodiversity
___: account for 50 - 80% of total biodiversity
Look at short doubling time. Expansion and cutting of primary forests. Very few places will remain undisturbed
Hypotheses for latitudinal gradients
Pure area effects
___: more area means more species
Tropical environments are "___" and have had more time to accumulate species.
___ rates are lower in tropics.
Higher net primary production in the tropics. Lotsa food
Tropical environments are more stable.
___ rates higher in tropics.
Tropical populations are more isolated.
Evolution is faster because more generations per year and more intense selection. Its generations, not years
Larger area, gonna have more species
Time-theyre older, never had glaciers, so have more species
Textbook organizes by processes
Spatial heterogeneity hypothesis
___: organisms in tropical regions have had more time to diversify under relatively stable climatic conditions
___: tropical regions have high spatial heterogeneity; more types of microclimates, vegetation, soils, etc. and thus contain more habitat types
___: more competition in the tropics leads to narrower niches and more species
___: predation intensity is greater in the tropics and prey populations are at low levels; thus interspecific competition never comes into play and rare species can persist
While these are nominally correct, the real way to think of this is in terms of disturbances, i.e. how these processes affect speciation and extinction rates
Species area effects
Number of species increases with area. Not gonna find the rare species unless we look really hard. Why we standardized for 50 hectares
Number of species per sample depends on area, effort and sample size.
S = C•Az
Effects of sample size in estimating diversity
Skewed distributions for species abundance means the number of species observed will be affected by sampling effort
Species accumulation curves
Area sampled, total number of individuals sampled, and total sampling effort affect the curve
Log-log plots for species-area relationships
S = C•Az
Log S = log C + z•log A
The pattern on islands
Size was attempted explained by MacArthur and Wilson
Theory developed by MacArthur and Wilson in 1963.
First experimental test by Simberloff and Wilson in 1966-1968.
Has had important impacts on conservation biology.
Accepted by conservationists and park planners
Used in design of wildlife preserves
Appears that Australia, Madagascar, Indonesia, the Philippines and Mexico are especially rich in endemic species relative to their land area