MARB 403 Lecture 3
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Banana Dolphin!
Grouping in Three Dimensions
Land animals group in two dimensions (examples of 3D grouping: birds, bats, fish)
- Aggregation (not facing same direction)
- Polarized School (facing same direction, doing same thing)
- Facultative (optional grouping; usually during day)
- Obligate (must stay together)
- Cooperative Society [1]
reasons for cooperation:
- food
- social/sexual
- detecting/avoiding predation (Most important aspect of sociality is predation; sometimes works to disadvantage)
- pack-hunting
- alloparenting
Dolphins use fish schooling behavior to herd them
- use echolocation to find at distance
- cooperate to herd into a ball
Silly (but important) Acronyms
- Evolutionary Stable Strategy (ESS)
- occurs all over the place in the Tree of Life
- Sensory Integration System (SIS)
- organism can integrate information from other organisms
- single member doesn't have to pay as much attention to watching for danger
- Advanced Confusion Effect (ACE)
- multiple animals amplify confusion effect
- visual illusion of motion that can give predator wrong information
- predators brain processes info incorrectly (like thinking a flagpole is falling over when looking up at it, but clouds are moving)
- Gaze Stabilization System (GSS)
- predator tries to circumvent ACE by staying with particular color and trying to pick individual out
- match motion to organism; minimize movement in relation to prey
Solitary ocean creature:
- cannot sense equally in all directions
- Dolphins, for example, cannot sense from below-rear
- if advance warning, might swim away with burst pulse/speed (skittering)
- surface is vulnerable: escape is only downward (toward an attacking predator)
More on Sensory Integration System
- ...
- passage of info through group
- individuality is submerged (negative effect)
Key functions to SIS:
- greater completeness of environmental surveillance
- faster reaction speed to predator
- mediates ACE
Aggregation
Asocial or Social: depends on whether animals are paying attention to each other
- asocial defined by where food is
Social aggregations can quickly become a polarized school, and then maybe a cooperative society
The more predators around → school
Individuals skitter When disturbed by predator: everyone darts in random direction
- The more predators there are, the more the aggregation breaks down
Scramble competition: the first member of a school to encounter food will try to get as much as possible
- after 7 or so fish, the scramble competition breaks down, and they start schooling
Polarized School
- Dilution effect
- More group members = lower probability of being eaten by predator
- Encounter effect
- Large group has a greater probability of being detected by predator
- Confusion effect
- Predator has a difficult time homing in on prey (e.g. flashing reflective scales)
Dilution and encounter effects balance each other
Cooperative Society
When dolphins are at rest or under attack, they behave like schooling fish (no individuality)
- Amoeboid evasive movement
- Individuals skittering
- Splitting of school and regrouping behind predator (fountain effect)
However, after the splitting phase, (4) Change of alert status: they wake up and start behaving like mammals
Echolocation
Has "freed" dolphins more than any other adaptation: allows them to be more social and playful
- highly coordinating, know each other very well
- advance detection of predators
- finding food, detecting prey
Marine Mammal Research
5 Phases
- Beached/stranded, dead animals
- Whaling ships (also research on dead animals, but limited behavior study)
- Captivity (mainly smaller marine mammals)
- Nature / wild (relatively new)
- Interdisciplinary (this is where I come in :) )
Bottlenose Dolphin Social Structure near Sarasota Bay
Randall Wells
Year-round residency in region
Movement corresponds to prey (and probably predators):
- summer: in shore, seagrass meadows
- winter: passes, gulf coast
Population is very stable, most well-studied population
Life History and Health
Length, girth, weight, blubber thickness
gender [2] determination
blood and milk sampling
- biotoxins (stored in blubber)
- contaminant transfer (milk)
- Firstborn gets the brunt of built-up biotoxins
age determination by tooth sectioning
- teeth grow in layers: group (GLG)
Male Sexual maturity
- testosterone concentration
- difference between sexual maturity and social maturity
- testis dimensions
Female Sexual maturity
- progesterone concentration
- mother's age at first birth
- births often happen during summer
- mothers can give birth between ages 6 and 49
Groups
Average group size appears to be smaller
Juvenile groups
- 3 yrs to teens
- mixed gender, but skewed toward older males
- play very actively (even into adulthood)
Alliances
- Bond formation at 11.1±0.7 yrs (sexual maturity)
- usually just 2 males per alliance
- annual coefficient of association = 0.75±0.03 (they spend much of their time together)
- 57.0±3.8% of all males are in an alliance
Non-allianced males tend to cover smaller areas
Alliance partners not selected based on relatedness (usually nonrelated)
Mean age difference is about 3.4±0.7 years
Alliance Advantage: better reproductive success
- Larger males tend to be more successful
Female Groups
Recent calves form nursery groups
- keep away males
- dynamic composition (often change from day to day)
Once youngster stops nursing, it ventures off to join another group
- Interactions with Kin occur, but are limited.
Evidence of learned behavior in feeding strategies
- "Kerplunking" — slapping surface with flukes or pecs to stun fish
- Tool usage: sponges as a glove to probe crevices
Few first-born calves (primiparous) survive
- toxin transfer
- Older mothers tend to do better (even punish youngsters)
Scientist of the Day
Randall S. Wells Chicago Zool. Soc. & Mote Marine Lab in Sarasota FL
Long-term study of Common Bottlenose Dolphins (since 1970s)
- 2-year gap in data because he went to Hawaii with Dr. Würsig
- Started work as undergraduate student
- Florida seldom gets Arctic blasts