Top down or bottom up
1 / 18

LastLecture - PowerPoint PPT Presentation

  • Uploaded on

Extinction rates on islands are related to the size of the island. ... Can raise more young if they migrate than if they stayed in the tropics. ...

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'LastLecture' - Kelvin_Ajay

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Top down or bottom up l.jpg

Page 496

Top Down or Bottom Up?

Bottom Up Control resources control community

N  V  H  P

Top Down Control  Predators control the community

N  V  H  P

Top down control = Trophic Cascade Model

Freshwater Pond For Example:

Phytoplankton  Zooplankton  Small Fish  Large Fish

Remove large fish then small fish increase, zooplankton decreases and phytoplankton increases.

Effects will be propagated up and down food chain as a +/-

Keystone species l.jpg

Page 471

Keystone Species

  • A species that occupies a specific niche that is extremely important in determining community structure.

    • When that species is removed, the community dramatically changes

    • Not typically the most common species in a community

Pisaster ochraceous a starfish l.jpg
Pisaster ochraceous (a starfish)

  • Keystone species in the rocky intertidal communities of western North America.

  • Is a strong predator for a mussel (Mytilus californianus)

    • The starfish can not eat large mussels, so the mussels have a size-related refuge from predation

    • This mussel can out-compete other invertebrates for space, but the starfish takes away that competitive edge.

  • When the starfish were removed, mussel numbers increased and excluded other invertebrates and algae from attachment sites.

Sea otters l.jpg
Sea Otters

  • Key Stone Predator in North Pacific

    • Once extremely abundant, reduced to near extinction in the early 1900’s by the fur trade

    • Feed heavily on sea urchins and thus can control their populations

  • Sea urchins feed heavily on macroalgae (kelp) and where sea urchin abundance is high, kelp is basically nonexistent

  • Where sea urchin abundance is low, kelp is common along with all of the other species associated with it.

Case study l.jpg
Case Study

  • Sea otters have declined (sometimes 25% per year) in Alaska since about 1990, and the kelp beds have begun to disappear as sea urchins increased.

  • Killer whales are suspected because their prey base (seals, sea-lions) has declined, and their predation on sea otters has increased.

  • Seals and Sea-lion population declines have been attributed to a decline in their food base (fish).

  • Fish declines have been attributed to overharvesting in the North Pacific.

  • So, overharvesting of fish may have led to a cascade of events that were unexpected.

Species area curves l.jpg
Species Area Curves

  • Species area curve predicts that larger islands will have more species than smaller islands.

  • S=cAzwhere

    • S = number of species

    • c = a constant measuring the number of species per unit area

    • A = area of island (in square units)

    • z = a constant measuring the slope of the line relating to S and A

Island biogeography l.jpg
Island Biogeography

  • Number of species (on a plot or island) is a balance between immigration and extinction.

  • If immigration exceeds extinction, then the number of species will increase.

  • Number of species usually at equilibrium

Island biogeography9 l.jpg
Island Biogeography

  • Immigration rates on islands are related to the distance from the mainland.

    • Close islands have greater immigration rates than far islands

  • Extinction rates on islands are related to the size of the island.

    • Extinction rates are greater for small islands than for large islands

Neotropical migratory birds l.jpg
Neotropical Migratory Birds

  • Neotropical = ‘New Tropics’

    • New World vs old world

    • Western Hemisphere

  • Neotropical birds breed in Canada and the United States during the northern hemisphere’s summer and spends the rest of the year in the tropics.

    • Defined as a species in which the majority of individuals breed north of the Tropic of Cancer (latitude = 23 degrees north)

    • About 200 species

Migration distance l.jpg
Migration Distance

  • Varies across species and within species

  • Shortest (a few hundred miles) are those birds that breed in the southern US and overwinter in Mexico.

  • Some of the longest are birds that breed in the arctic tundra in northernmost Canada and winter as far south as the southermost tip of South America

    • One way mileage = 10,000

  • Arctic Tern

    • Nests as far north as land extends

    • Overwinters near the south pole

    • Sees more daylight than any other species

    • Round trip covers about 22,000 miles.

Why migrate l.jpg
Why Migrate?

  • They can take advantage of seasonally abundant food supply and avoid times and places that food supply is low.

    • Flying insects, caterpillars, fruits and nectar are abundant during our spring and summer, but not winter.

  • Ultimate reason is breeding success.

    • Can raise more young if they migrate than if they stayed in the tropics.

    • Abundant protein-rich food, longer daylight hours, more room, possibly fewer predators.

When to migrate l.jpg
When To Migrate?

  • Internal clock controls the onset of migration and the premigration preparations.

  • Environmental factors control this clock

    • Certain changes in a bird’s environment stimulate the production of certain hormones, which leads to changes in behavior and physiology.

    • Change in day length for example

How to get there l.jpg
How To Get There?

  • Short migraters and waterfowl generally learn breeding and wintering locations from older more experienced birds

    • Often family members

  • Most long distance migraters are genetically programmed to make the trip.

    • First migration is completely under genetic control

    • Subsequent trips may incorporate previous experiences (return each year to good reproductive grounds)

Migration routes l.jpg
Migration Routes

  • Follow land through Mexico into the United States

  • Cross the Gulf of Mexico

    • First/last encountered land important to survival

    • Rest and refueling

Seasonal habitats l.jpg
Seasonal Habitats

  • Wintering Grounds

    • Sufficient food for premigration preparations

  • Migratory Habitat

    • Fat reserves, nutrients, vulnerability to predation

  • Breeding Grounds

    • Reproductive success

Habitat variety important l.jpg
Habitat Variety Important

  • With the diversity of migratory birds, a diversity of habitats is needed in the migratory habitats.

    • Reduces competition