Resource acquisition by societies part 1 Flashcards
what do animals need to balance when deciding when and where to forage for food?
- time
- reward
- risk
what does optimal foraging seek to explain?
it seeks to explain the diversity of approaches to foraging based on the costs and benefits of alternative strategies available to an organism
define Central place foraging
a mode of foraging where the forager must return to a central location to process, consume, store and/or share food resource
what benefit/cost do greater foraging distances provide?
- benefit of more food and a greater variety of food types
- cost of time, energy expenditure, and risk
What kind of decisions do foragers have to balance?
- How long to look?
- How hard to work?
- Once food is located, how much should be retrieved?
- How quickly should it be retrieved?
Central-place foraging is the foraging mode for what kinds of organisms
any shelter-building social organism, and many others with a well-defined core area
Having a shelter and central-place foraging may allow what?
it may allow new food types
Having a shelter and central-place foraging may allow new food types - Many group members may what?
further facilitate access to new food types
Having a shelter and central-place foraging may allow new food types - tradeoffs of having many group members
a subset of all society members must feed the whole society
Having a shelter and central-place foraging may allow new food types - what is the cost for the tradeoff
- cost is that individual foragers must forage longer and further from the central location than a solitary organism would
- time, distance, and risk costs are amplified
Central-place social foraging - Example
leaf-cutting ants
central-place foraging - leaf-cutting ants
A leaf-cutting ant forager may travel several hundred meters to a foraging site
central-place foraging - costs
- Time and energy spent foraging
- Increased forager mortality rates
central-place foraging - which social traits offset the costs?
- Division of labor
- Foraging specialization tied to increase in age and/or a decline in fecundity
what do individual strategies in social foraging do
Balances the costs and benefits of foraging at the level of individuals
individual strategies
- Search behavior.
- Orientation mechanisms.
- Load size.
- Morphological adaptations.
search behavior - define Correlated random walk
Each subsequent step is in a random direction, but with a degree of correlation to the previous direction of movement.
correlated random walk - Optimal turning angle (tortuosity) depends on what?
the probable distribution of food sources and the number of cooperative searchers
correlated random walk - Encounters with other group members or lack of food favors what?
favors straighter search paths and greater distances
correlated random walk - how do single foragers perform optimally
they use a tortuous search path to maximize area coverage around the “central place”.
search behavior - example
silver desert ants
search behavior: silver desert ants - What pattern of tortuosity and social coverage do they engage in?
- They move in different directions to cover more ground
- They all typically maintain a straight movement (less tortuous path/shallower angle)
search behavior: silver desert ants - What might we predict about foraging distance and food availability from their tortuosity
- Widely scattered food
- Food is not near the nest
Once food resources are acquired, how does the individual return to the central place?…What are the possible mechanisms of orientation back to the “central place”?
- individual orientation
- can involve a combination of 4 things
Individual orientation can involve a combination of what?
- Visual cues.
- Acoustic communication between group members.
- Chemical orientations.
- Biomechanical detection of distance.
individual orientation - visual cues example
honeybees
individual orientation: visual cues - how do honeybees estimate distance
“Strobing” of images past the bee is used to estimate distance
individual orientation: visual cues - honeybee experiment
the bee flies through a tunnel where the visual pattern can be manipulated.
individual orientation: visual cues - what does manipulation do to the honeybees
Manipulation of pattern to reduce frequency of image cues reduces distance estimates by bees.
individual orientation: visual cues - result of honeybee experiment
A visual “odometer” from environmental visual cues is used in bee orientation and distance calculation.
individual orientation - what is the most reliable and simple mechanism?
retracing path along persistent path route
individual orientation: retracing path - Path persistence can include what
- Remembered path, typically via landmark orientation.
- Physical and/or chemical signature from outbound journey
individual orientation: retracing path - What’s the main cost of retracing outbound path?
The retraced path may be longer than it actually is
individual orientation - what does path integration involve?
it involves the use of outbound journey information to calculate a straight(er) return route of known direction and distance.
individual orientation - path integration example
silver desert ant
load size - what do social mammals tend to do?
tend not to retrieve and instead rapidly consume and defend in place
load size: social mammals - if retrieval does happen, what should selection favor?
selection should favor maximum load size that does not hinder the overall efficiency of foraging strategy
load size - define “load matching”
loads are matched to body size but are still small enough to not hinder retrieval speed.
load size - when is “load matching” common
in social animals that retrieve resource loads
Contrasting examples load transport with load-matching
army ants vs leaf-cutting ants
contrasting examples load transport with load-matching - army ants
- Faster than leaf-cutting ants
- Collaborative behavior
- Carrying prey below body
contrasting examples load transport with load-matching: army ants - what are the benefits and costs of carrying prey below body
- benefit: can carry heavier items
- cost: must fit below the legs
contrasting examples load transport with load-matching - leaf-cutting ants
- A lot slower than army ants
- More individualistic with load carrying
- Carry prey above head
contrasting examples load transport with load-matching: leaf-cutting ants - what are the benefits and costs of carrying prey above the head
- benefit: can carry bigger pieces
- cost: move a lot slower
Morphological adaptations for foraging - in social mammals
primary tools are teeth and claws.
morphological adaptations for foraging - in social insects
primary tools are the mandibles and sting (or other chemical weapons)
Morphological adaptations for foraging are heavily dictated by what?
- heavily dictated by the evolutionary history of the group
- but are often enhanced in the context of social life.
Morphological adaptations for social foraging - example
- porter caste in army ants
- social dogs vs social cats
morphological adaptations for social foraging - porter caste in army ants
- has specialized mandibles, big heads, and long legs
- evolves in species that carry awkward prey
- but must “fit” in the developmental space between workers and soldiers, so morphological traits are constrained by evolutionary history.
morphological adaptations for social foraging - social dogs
Run prey to exhaustion and use teeth for take-down
morphological adaptations for social foraging - social cats
High-speed prey capture with teeth and rotatable, clawed paws.
