Top down or bottom up
Download
1 / 18

LastLecture - PowerPoint PPT Presentation


  • 164 Views
  • 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. ...

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


ad