Choosing Where to LiveChapter 8or

What side of the fence IS the grass greener on?

Choosing Habitats

Fact: animals generally actively choose habitats, patches, etc.

This is shaped by natural selection

True or False Most animals have a instinctual ability to prefer proper habitat?

True

Choice of Where to Feed, etc.

no competition for food

no depletion of food

20 J/hr 10 J/hr

Choose A

Patch A Patch B

Ideal-Free Model of Habitat/Patch Choice

Ideal – animals know everything about food

Free – free to move anywhere

Key points:1. animals will have a preferred habitat

2. But will not necessarily choose that habitat (due to effects of competition).

All organisms are identical with no fighting over resources.

Testing IFD with Fish

Can vary food addition of feedersAssume maximizing fitness is maximizing rate of energy intake.At the IFD, all animals will have roughly equal energy intake rates.

Ideal Despotic Model of Habitat Choice

It’s all about monopolizing resources

Allow individuals to monopolize sites within habitats – ie. territories.

Some individuals can defend high quality patchesNo longer “free” to go where you will.

More realistic situation

Tested with Aphids on Cottonwood popular treesThese aphids can reproduce asexually as clones or

sexually.Sexually reproducing aphids are gall formersFemales fight for position on leafBest spot is at petiole of leaf

3

2

1

8.6 Poplar galls are occupied by poplar aphids

8.8 Territories and reproductive success

Ideal Despotic Model

2nd is worse than 1st, but may be better if it is a big leaf.

With 2 habitat patches – there are not always more on the best

BA

Chosen 1st

Moreindividuals

Questions

True or False The best habitats will always be entered first.

True or False Will the best habitat always have the most individuals

Depends on the size of the habitat and competition between individuals

True

Reading Assignment pp249-263

What are the sexual differences in dispersal

Contrast mammals vs. birds

Why Voluntarily Disperse?Inbreeding avoidanceLocal competition

How far to disperse?Out-breeding depressionAvoidance of competition

What factors might cause an animal to change breeding territories from one year to the next?

What are the costs and benefits of long-distance migration?Migration in Monarch butterfliesGeneral natural history of migrationWhy do monarchs migrate all the way to Mexico?

Dispersal Migration

More discussion on these topics to come later

Territoriality

Home rangeArea of activity

TerritoryExclusive area defended from intruders

Questions to ask?Whether to be territorial?

How to be territorial?

Benefits of Territoriality

Reproduction

Energy

Reproduction

Remember the fighting aphidsRemoving others from leaf can allow a greater number of offspringDon’t fight due to cost in energy, time and injury.

BirdsNo territory = no breeding for most birdsDemonstrate many non-breeding floaters

No territory

Don’t fight for territory because they are young and can try to breed next year or the next

Florida Scrub-Jays pages 117 - 124

Energy

Territories outside of breeding seasonOnly defending food (energy)

Energy = fitness

Seen in some birds and some mammals

Ex. Nectar feeding birds (simple food source)Food source easily characterized and defendable

Golden-winged Sunbirds

High quality territories are very beneficial to ownersStable food source

Energy needs met in short time

But not always territorial

Territorial sunbirds

Flower Density - territories abandoned

Cost to defend larger area is too high

Flower Density - territories abandoned

No net benefit, plenty of food

Territoriality occurs at intermediate flower densities

Intruders Rate - territories abandoned

All time is spent defending

Territory Size

Cost / Benefit Approach

Minimal Territory Size

m = metabolic cost of owner

c = energetic cost of defending territory

f = food density (or energy) (energy/m2)

Territory size (minimal) = (m+c)/f

Territory Size as a function of food

1/f

Ter

ritor

y si

ze

Food density

size α 1/f

Territory Size to Maximize Energy Gain

Graphical model of optimal territory size.

cost

Benefit (can’t use it all)

T1T*

T2

Territory Size

Cos

t or

Ben

efit

T1 = min territory sizeT2 = max territory sizeT* = max energy gain (max = B-C) slopes are equal at this point - Break even when lines cross

Example

Hummingbirds increase territory size before migration to gain weight

In many cases, the environment may be saturated with territories that persist for long terms.

Effects on Territory Size

When food density declinesMay be very little change in sizeCost of expansion is too highRemoving owners from their own territory

When food density increasesCould see small territory sizeBut, re-expansion may be difficult

Often see no change at all in size - stay as you are!!

Unchanging Size in Pied Wagtails

Non-owners feed in nearby fieldsWhen food density in fields declines, they go

to the riverOwners cannot decrease or stop being territorial

Owner lets only 1 intruder onto territorySatelliteHelps with territory defense

Stay 180° apart on opposite sidesWhen intruder density decreases – satellite is

removed.

territory

Dispersal

CostsExposure to predators

Requires energy

Benefits1)Inbreeding depression

2)Reduced mate

competition

Inbreeding Depression

Less likely for recessive genes to be expressed

Females bear more of the energetic cost (avoid relatives)

Males disperse to have more mates

Female mammals hold territory and get help from another (ground squirrels), safe breeding den.

Mate competition

Males fight – loser moves on to find another mate

Not true for ground squirrels – happens before fighting

Winning males move on to avoid sexually mature daughters

Male lions leave (or forced out) when a new male comes into area

Bird Dispersal

Males return when previous year was successful

Disperse and move toward a more successful future if unsuccessful previous year

MigrationOccurred graduallyFirst with short range migrantsFollowed by long range migrants

(continents)

8.14 Short-range migration in the three-wattled bellbird (Part 2)

8.15 Distribution of Catharus thrushes, a genus with both resident and migratory species (Part 1)

8.20 The two migratory routes of Swainson’s thrush

Costs of Migration

EnergeticPredators – group dilution

effectCross Mediterranean at Spain

– narrowest partCross Atlantic when possible,

if decreased body fat, go over to Mexico

Black poll warbler – across Atlantic – shorter, few predators, and tail winds

Benefits of Migration

Seasonality allows for bursts of food to support young

Fishbreed in freshwater

Tropics – more food in freshwater

Move to breeding ground (saltwater)

Monarch Butterflies

Central Mexico Oyamel fir forest

Less likely to have sudden freezesMoist and cool to maintain energy

reservesTree removal exposes them to rain and

cold night sky

Increased risk of freezing, exhaustion, and desiccation

8.22 Habitat quality and survival of monarchs overwintering in central Mexico

Migrants and Non-migrants in Same Species

Exactly the same fitness in the long run

The 2 Strategy HypothesisDifferences are genetic

Don’t change behavior from year to year

Equal fitness on average

Actually, individuals switch behaviors

Territoriality and Dominance

Implies site-specific dominance

Owner is dominant individual only on its territory

Owner almost always wins in a dispute

Payoff Asymmetry Hypothesis

Owner places a higher value on

territory than an intruder will

Owner is more willing to fightIntruder immediately retreats from

Confrontation Intruder is looking

for free territory

ExampleCapture territory owner male bird

Hold it for a bit in an aviary

Territory taken over by another individual (floater)Let it hold the territory for a few

days

Release original owner back into territoryBIG FIGHT

Original owner almost always wins eventually

Not the case in butterflies.

Resource Holding Power HypothesisOwner wins because they have superior ability to

hold territoryTerritory owners are the best fightersEx. Damselflies

Fat reserves (not body size) dictate the winner in contest, more fit gets the territory.

Other Topics

Domains

Interspecific territoriality

Domains

An incompletely defended territory

Defend center stronger that edge/marginal territory

CoreTerritory

Te

nd

en

cy t

o

evi

ct

intr

ud

ers

Distance from center

Interspecific territoriality

One species defends territory against several other species.

Unusual in nature

Seen in territories during non-reproduction (ie. food defending territories)

Aggression should be diet specificMockingbirds run off other fruit eaters, but ignore

insectivorous species.