Foraging Ecology Flashcards
Foraging
The process of finding wild food resources
What does foraging entail?
Decision making regarding how, when, and where to find food
What are some life history constraints on foraging?
Seabirds feed at sea but raise their young onshore
Stomach Oil
- Found in the proventriculus of procellariiformes
- Composed of dietary lipids
- Made up of waxes, esters, and triglycerides
What is the significance of stomach oil?
- Light
- High caloric density
- Replenishes water reserves
Describe the optimal foraging theory
Maximize energy gain to enhance fitness
Describe the two foraging strategies of breeding albatrosses
- Short trips
- Long trips
What is the significance of short foraging trips?
- Energetically beneficial to the chicks
- Energetically costly for adults
- Close to breeding colony
What is the significance of long breeding trips?
- Maintain parental body mass
- Lower food delivery rates for chicks
Intraspecific competition
Competition for limiting resources during nesting season
Interspecific competition
Competition for limiting resources year round (cooperative feeding)
How does sexual segregation affect seabird prey and foraging habitat (use Northern Giant Petrals as an example)?
- Females are smaller than males
- Females eat fish, krill
- Males = scavengers ( eat carcasses)
Resource partitioning
Different organisms within one ecosystem forage on different prey types in different areas so that there is limited competition for resources
What are examples of resource partitioning?
- Crested auklets (upstream), parakeet auklets (middle), least auklets (downstream) forage in different areas of the ocean
- Sexual segregation
- Habitat partitioning
Internal constraints to foraging
Physiological limitations such as:
-Flight costs
- Diving costs (ADL)
External constraints to foraging
Factors affecting prey:
- Prey size
- Caloric density
- Predictability
- Accessibility
- Aggregation of prey
What oceanographic features can affect foraging movement?
- Fronts
- Eddies
- Upwellings
How can oceanographic features affect foraging movement?
Oceanographic features –> Aggregate prey –> Attract foraging predators
Fronts
Regions with enhanced gradients of hydrographic properties (temperature, salinity, nutrients)
Oceanographic Hotspots
- Upwelling
- Sea mounts (rise in elevation of the sea floor)
- Convergence zones
- Shelf / coastal areas
Convergence zones
Different water masses come together resulting in downwelling which causes prey items to float and aggregate in surface waters
How are oceanographic hotspots related to productivity?
Productivity generally increases near an oceanographic hotspot
Coastal upwelling
- Surface water = being forced offshore by prevailing winds (Coriolis effect: water moves perpendicular to direction of wind)
- Brings cold, nutrient rich water to the surface (photic zone: where photosynthesis occurs)
- Productivity = increased
Describe the general conditions of coastal upwelling systems
- Low temperatures
- High O2 content
- High nutrient contents
Cyclonic eddies
- Counter clockwise
- Cold core eddies
- Northern hemisphere
- Cold water is upwelled
- Prey is aggregated
Anticyclonic eddies
- Clockwise
- Warm core eddies
- Cold water is downwelled
What meso-scale oceanographic features can be measured from space?
- Satellite altimetry
- Current measurements
- Chlorophyll measurements
Satellite altimetry
Measures height of sea surface
Current measurements
Determines how rings of eddies are rotating
Chlorophyll measurements
Measurement of biological productivity (more chlorophyl = higher productivity)
Describe how Great Frigate birds utilize eddies
Target the edge of eddies where prey aggregated at the surface
Frigate birds cannot land on the water
Gulf Stream Rings
- As Gulf Stream moves offshore meanders form
- Meanders drive formation of eddies (below Gulf Stream)
- Eddies = cold core (cyclonic)
- Results in upwelling
Describe a fine scale oceanographic feature in Phalaropes
- Surface feeders
- Spinning behavior
- Generates upwelling of prey which is aggregated at the bottom
Only effective in shallow waters
Copepods
- Phalarope prey
- Lots of lipids
- Located at depth of 50 to 150 m in the Bay of Fundy
Why is this a problem
Bay of Fundy
- Largest tidal currents in the world
- Tidal currents hit ledges creating vertical mixing
- Creates upwelling and fast current speeds (above ledges)
- Low surface temperatures (due to upwelling)
- Aggregates copepods in surface water
How do oceanographic features affect diving birds (ex King Penguins)?
- Associated with fronts
- Feed on prey aggregated in frontal regions
How are foraging skills learned in seabirds?
- Acquired gradually
- Long period after fledging
- Breeding is not attempted until foraging is successfully learned
- Must learn to recognize physical biotic features of ocean as indicators of food
How does age affect foraging proficiency?
- Adult birds = more proficient foragers than juveniles
- Maturation = delayed until foraging skills = acquired
- Foraging proficiency = gradually increased with age
El Niño
- Trade winds (east to west) weaken
- Warm water is pushed East
- Pacific Jet stream moves south
- Results in little to no upwelling of nutrient rich cold water
La Niña
- Trade winds are stronger than usual
- Warm water is pushed West
- Pacific Jet Stream moves North
- Results in increased upwelling but warmer temperatures
Transition zone chlorophyl front (TZCF)
- Cold more productive waters in North
- Warmer less productive water in South
- Important foraging area for albatrosses
How does the TZCF affect albatross breeding seasons?
- Location is further South during breeding season (closer to foraging area = shorter distance to travel)
- North = longer distance to travel
How does El Niño affect oceanographic features?
- Temperatures cool
- North Pacific Gyre contracts
- TZCF = further South (less distance for albatrosses to travel while foraging)
- High reproductive success
How does La Niña affect oceanographic features?
- Temperatures warm
- North Pacific Gyre expands
- TZCF = further North (larger distance for albatrosses to travel while foraging)
- Low reproductive success
How is albatross reproduction affected by La Niña?
- Reproduction decreases
- TZCF = far North
- Less food goes to chicks (longer foraging trips)
- High sea surface temperatures (poor foraging conditions)
