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BEHAVIORAL ECOLOGY
(Biol 607)
Fall 2004
Lecture 6: Spacing and Territoriality II
Living in Groups
TEMPORAL DISTRIBUTION
-
dimension also important
- Are resources
?
TERRITORIALITY evolves as resources become
> Costs
Ex)
- Old World passerines, convergent with hummingbirds
- nectarivores
- defend areas with
- Note: undefended areas are lower in quality over
the course of the day - no competitor exclusion
Ex 2)
- Hawai’ian passerines, impressive
, closest ancestor Fringillidae
- too few resources:
- too many resources:
- intermediate levels:
of defense
> cost
GROUP LIVING
- as with territoriality, various
- costs of sociality can be significant:
- increased likelihood of
- increased competition for:
- increased risk of
- therefore
and
must be high:
- KEY: must view behaviors that are advantageous
to
first;
and secondarily to the
BENEFITS:
1.
Protection from
Ex) homeotherms up to 117 in cavity in winter
(cost:
)
- cactus wrens

- huddling
- largely
energetic savings
2. Protection from
through various means
-
: many additional eyes,
noses, ears for detection
ex)
:
flocks had lower kill probabilities
and greater detection distances
-
: reduce
vulnerability
via mass response
ex)
flocks:
lone individuals very vulnerable
numbers safer
large flocks - birds
(also a vigilance aspect to this example)
ex 3) - Combination ?
(Mollusca) and fish predators
less successful hunting groups
Clear
to group living
!
- Selfish Herd: Hamilton
Appearance of cooperation to elude predation
due to individuals acting competitively (selfishly)
- One animal uses another as a shield
selecting for the shield to behave similarly
 aggregations of individuals
DRAW
- individuals on periphery most vulnerable
- direct competition for central (safe) positions
- Why take periphery?
young and/or subordinate animals
ex) snow geese at Funk Lagoon
ex) predation observation at Bosque del Apache
ex) snail predation on bluegill sunfish nests
HANDOUT
- solitary nests higher number of snails
(snails and bullheads are predators)
fewest number of defense chases
- central nests lowest number of snails
highest number of defense chases
- Dilution:
overwhelm consumption capacity of local predators
 evolution of synchrony
ex) seabird colonies
sea turtles
aquatic emergents
Ex) mayflies - when more emerge synchronously
chances of any 1 individual female surviving increases
HANDOUT
FORAGING ALSO LEADS TO BENEFITS OF AGGREGATING
Ex) Jarmen’s model of social organization
in African ungulates
Total of 81 mammalian herbivores
Artiodactyla -
Bovidae: 78 spp
Suidae: 3 spp
Perissodactyla - rhinos and zebras: 6 spp
Proboscidea -
elephant - 1 spp
Subdivide available resources
Note: in Serengeti Park alone 27 species of carnivore!
Relationship between foraging ecology and group size
FORAGE TYPE
 
SPATIAL DISTRIBUTION
 
TERRITORIALITY or
LARGE GROUPS
 
GROUP SIZE