Transcript The Ecology of Finding a Place to Live

Chapter 6
1. Habitat selection - selection of a particular
area in which to live
2. Territoriality - defending your habitat
3. Dispersal, migration and homing - when
suitable habitat is not available nearby
4. Nest Construction – making own habitat
1. Observation: if you go out in nature,
one finds specific animals usually
occur only in specific locations. If you
compare species of animals in an
open field to those found in forests, you would
find most are different.
2. If you allow animals to make choices about the
type of area they live in, one finds that even
single celled animals are discriminating choosing to live in particular locations and not
others
European songbirds:
 coal titmice - live in pinewoods (pine trees)
 blue titmice - oak woodlands
She hand reared baby coal tits and blue tits
until they could fly
And placed young birds in a cage with a
"composite" branch
 oak and pine portions of same branch
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% Time
100
50
Blue
Wild
Coal
Blue
Coal
Hand-Reared
1. an animal may be best adapted
(anatomically or physiologically) to feed or
reproduce in a particular area - selection
favors animals that also prefer to stay in
these areas
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factors restricting habitat use:
a. climate, physical +/or chemical factors,
competition, predation, location of food, etc.
Ex. Polistes nests - picked off out in open
Ex. Competitive exclusion: barnacles
Chthamalus stallanus - high on rocky shores
Balanus balanoides - lower on rocky shores
Remove Balanus, Chthamalus moves in. Balanus
smothers and crushes Chthamalus (Connell 1961)
Cottonwood aphids - Utah
Tom Whitham
In spring, eggs (laid previous winter)
hatch and from them females about
0.5mm long emerge
Females walk along trunk and branches of tree to a location
where a batch of leaves is just starting to form.
Female chooses a leaf and induces the formation of a hollow
ball of plant tissue (gall) to form along the midrib.
Aphid lives in gall - first batch of eggs are
female.
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Larger the leaf - the more female offspring
produced and the greater their average
weight
One would expect females to select only large
leaves when given a choice (assuming that
their behavior has been shaped by natural
selection) Is this what they do?
If so, what happens if there is competition for
the good leaves?
1. Average Density = 35 aphids / 100 leaves
- about 2% leaves = large, 33% = small, the rest
(65%) were in between - none of the small leaves
were utilized
Conclusion:
-Aphids use large leaves disproportionately more
than small. They are able to tell which leaves are the
best and choose those that will be the most
productive and support the most offspring.
-But what happens if a large leaf is not available?
2. some will double up or triple up on the same leaf;
Late comers end up farther out on the leaf and
therefore don't get as much of the flow as the first
female
No. of Galls
per Leaf
Mean Leaf
Size (cm)
Mean Number of Progeny
Produced
Basal
Female
Third
Female
Second
Female
1
10.2
80
2
12.3
95
74
3
14.6
138
75
29
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½ workers & old
queen swarm
Scout bees search for
new home
◦ Each dances to direct
others to potential site
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One site chosen
Everyone leaves
together & flies to the
new nest site
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Preferences:
◦
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Small entrance – 12 cm2
Entrance – south facing
Ht of nest – 5 m min
Cavity volume – 40 liters
Scouts inspect entrance,
walk around interior
◦ Distance walked relative to
the cavity entrance was
experimentally shown to be
basis of bee’s estimate of
cavity volume
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Tom Seeley set up box
choices on treeless island
Transported swarm and
studied decision process
◦ Scouts recruit only for a
short time – so voting for a
site can fade away if new
recruiting scouts aren’t
picked up
◦ Best site is not always
picked
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Neutral bees become
supporters for a site in
proportion to the number
of bees dancing for that site
◦ Scouts do not stop dancing
for their site after visiting
another site
◦ They just stop recruiting after a
while & become quiet
◦ This loss of motivation allows a
less supported site to fade out
of the “debate”
Regular - even spacing of
individuals in an area (territorial)
Random - rare
Clumped - social groups,
family groups, mating clusters,
etc.
An area or space, which is defended
through aggression or less overt
behavior against other organisms.
1. What is defended? May be a piece of
land (Cardinals, Red Winged
Blackbirds), a resource (Acorn
Woodpeckers), or simply space
around animal of same species
(stallion / herd) - or more unusual
space around another species:
ex. Bitterling (small fish) territory is centered around moving
clam
2. Defense may be through
active fighting or aggressive
displays – antlered flies or
by means of chemical markers
which are not as obvious
- dogs, cats
3. Territory may exclude animals of same
species or other species, including plants.
ex. Acacia ants - live in thorns, they defend
their homes and the nectaries the plants
provide from other ants, grazing animals and
also from competing plants in the area
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Using Optimality Theory – should occur when
benefits outweigh costs
The cost of defending the area:
if around a resource
◦ How many competitors?
◦ How dispersed is the resource?
◦ How predictable is resource?
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The benefits of defending the area
◦ What is gain in resources?
◦ Does it help in attracting a mate and improve
reproductive success?
1. When there is a resource worth defending:
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Predictable in time and space
Defendable given the number of competitors.
Concentrated or rich resource
Benefit is greater than cost of defending
2. Territory may be required for reproduction
(high reproductive benefit)
◦ wide range of species - typically males set up
small display territory (known as a lek) where
they can display themselves, females choose
among them
Some defend permanent territories where food is
predictable and abundant. They defend both
sides of a river and collect food washing up on
the bank.
- If area is very rich, a partner or young may be
allowed to share, but chased off if resources
dwindle.
- Interestingly, some of same species feed on
transient, patchy food supplies - when this is the
case, they feed in flocks
ex. Chipmunks - J. Brown - Nevada
2 sp.: Eutamias dorsalis - open terrain, territorial
E. umbrinus - forest, no territories
- Where they occur alone, there is no difference in habitat
elevation. Where they overlap, E. umbrinus is at higher
elevations. There appears to be competitive exclusion.
Experiment: placed peanuts out in areas of near overlap
In open terrain - E. d. does better - aggressively defends
food dish from others, can see them approach from far
away
In forest – E.u. does better. Aggression spent in vain,
while chasing off one, another dashes in and feeds, with
dense brush, several can get very close to dish
a. wide range of species do this - typically
males set up small territory (known as a lek)
where they can display themselves, females
choose among them
Lekking species include: birds, frogs,
antelopes, bats, dragonflies, and many
species of flies.
ex. sage grouse - males stand out in
area, individual stamping ground,
puff feathers, and call or stamp feet
- display areas are often traditional
- typically in a lek central males mate
with the most females (80% by 3
central males in group of 10?)
- female preference, forces males to
compete for these locations and
thus the females automatically get
the strongest male.
a. Territories exclude others.
- If resources or nesting areas and /or mates can
be monopolized by one or a few individuals, they
will survive and reproduce more successfully than
those without territories
Why do excluded individuals tolerate exclusion?
- If exclusion means loss of mates or food, why
are most territorial disputes relatively harmless.
- most exclusions are temporary - one breeding
season, one area of food abundance. In insects
with just one reproductive season, - small males
may use alternative strategies.
- territorial holders have alot at stake in dispute will tend to fight much harder than newcomer
- newcomer will do better if as soon as it is fairly
clear that s/he might get hurt in the fight, s/he
runs away. If s/he stays and fights, s/he risks
injury and potentially total loss of reproductive
success.
- what one finds is that usually surplus males
and females = young individuals - waiting
their turn
 tits, sparrows, impala, elephant seals, others
Dispersal:
 Often young disperse
◦ Often males (Belding ground squirrels), may be
female (Florida scrub jay), maybe both
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Costs may be high – energy, exposure to
predators, finding resources in a new place
Benefits are high
◦ Avoid inbreeding depression (lowered fitness from
mating with closely related individuals)
◦ Avoid competition with parents
◦ Avoid aggression from older same sex individuals
Ex. Migratory locust (Schistocerca gregaria) of
N. Africa and Middle East
Two races:
1. normally live in a solitary fashion, cryptically
colored
2. swarm forming, long-distance movement,
brightly colored, eats anything
High density or If given diet of other locust tend to get 2cd race
At intervals of several years, fluctuations in
weather lead to a reduction in the size of the
population in favorable areas. When such a
reduction follows a period of population buildup,
the locusts are concentrated and the gregarious,
dispersing race is produced.
Once dispersal is in full swing - swarm may be as
many as 10,000 million individuals, travel a total
of 2000 mi (tend to move downwind).
- to sustain flight locusts may consume their
body weight in plant material per day. Large
swarms may weigh up to 50,000 tons or more.
Latin equivalent of locust means "a burned place"
a. Why?
1. Avoid bad climate during winter or dry season
2. To maintain a source of food
- decrease due to onset of winter or dry season
- buildup of population density = dispersal
_ egg laying site is different from foraging area
a. Why not just stay in tropical zone (warm and food avail)? 1. Temperate zone - spring and summer - large increase in plant
and insect pop growth = excellent resource if taken advantage
of. Same can be said of an area that has wet and dry seasons
2. Stiff competition in wet tropics, great species diversity
3. Compromise: overwinter in acceptable area, breed in rich area
with lots of space for breeding
1. Arctic tern - 25,000 mi round trip each year
(longest known) - flies 8 mon/yr
a. Breed in Arctic summer (long days, lots of
food), overwinter on
islands in
the Antarctic
Sea
2. Many mammals: wildebeest, caribou, seals,
whales - same reasons
Ex. Buffalo = migrated between Canada and
Mexico in large herds
- between 1870-1875 12.5 million were shot
(tongue = delicacy, carcasses were left while
indians starved)
- by 1889 pop. = 1091 today = 30,000
Insects - Monarch butterflies
- Northern breeding areas, southern
overwintering area
-
overwinter in very specific small areas - coast
of California, LA to Monterey, and just north
of Mexico city at
an elevation
of 9000 ft.
a. None - travel with prevailing winds
ex. Migratory locust
b. Topographic features - visual and chemical cues
Ex. Salmon
- born in mountain streams, swim to
ocean, live several years
- return to natal stream to spawn and die
- learn smell of river as fry and learn olfactory
characteristics of currents near river mouth
Ex. Digger wasp (Tinbergen)
1. Orientation alone - no biological clock
involved
Ex. northern butterflies (Painted Ladies) fly at
an angle to sun only during limited hours of
the day even so path looks like:
- sun as a compass
heading in conjunction
with clock
- angle travelled is
with respect to the
sun, but that angle is
corrected for the
movement of the sun
Ex. pigeons - clock
allows the birds to fly
in a straight line
Ex. Honeybees –
communicate location
of food with respect to
the location of the sun
Ex. indigo buntings (Emlen)
- learn star pattern - orient with respect to the
star around which others rotate: northern star
Ex. birds and bees
- magnets attached to (pigeon) heads alters their
orientation.
Ex. Heart and Dart Moth (Agrotis exclamationis)
(Robin Baker,1987) moves across country
- Moth used the geomagnetic field to calibrate a
moon compass. Directional preference changed
such that it tracked the change in the moon’s
azimuth. 1) Orients to geomagnetic field; 2) Sees
the direction of the moon; 3) Rest of night flies
according to the moon.
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a. some bird nests are primitive "structures"
- slight depression in dirt
b. Some termite nests are so
elaborate, no one fully
understands how the
builders can coordinate
their building efforts to
construct it.
Ex. Macrotermes bellicosus
Compass termite nests get up to 5m high and
3m long
-broad sides face east and west
-narrow surface = north and south, so get little
exposure at mid day
-wide sides = maximum surface for sun
warming early and late in the day
-how are nests oriented?
they are sensitive to
earth's magnetic field,
Example of behavioral radiation and the effects of
predation on shaping that behavior (Jeanne 1975)
- much variability
a. two types - open and enclosed
b. major predators = ants, which once they find
brood can recruit many
helpers and decimate
a wasp
nest
c. ant guard
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Stimergy – inherited building
program
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Learning - Weaverbird nests