Habitat Selection,

Territoriality, and Migration

Where to stay, when to leave and where to go…

Habitat Choice• The choice of habitat effect’s an animals behavior

(anti-predation strategies, foraging behaviors, mating opportunities, etc.), but the animal’s behavior effect’s it’s choice of habitat as well.

• When we considered foraging there was really only one driving force, the availability of food, but with Habitat choice, there are several important factors, for example: food, mates, predation, temperature/shade, building materials, etc.

• Habitat choice decisions are complex and multidimensional.

Some Habitat Terms• Home Range: a large area where an organism

spends a lot of time (but not much time in any one part of the area), and does not defend the area from use by other individuals.

• Nomads: individuals that continually wander and never return to the same place with any regularity.

• Territory: an area regularly occupied and defended by an organism. Territories are generally a small part of an organism’s home range.

More on Territories• Some organisms can occupy territories and home

ranges for an extended period of time. What constitutes a long period of time of course is relative. Florida Scrub Jays for instance can occupy and defend a territory for several years, and pass that territory down to their offspring.

Abiotic vs. Biotic Forces

• In some cases abiotic factors dominate habitat choice, for example: heat, availability of water, wind, refuge from danger, availability of specific nutrients, etc.

• In some cases biotic factors dominate habitat choice, for example: location of mates, food, predators, parasites, etc.

• For certain, both abiotic and biotic forces interact to determine habitat selection and territoriality.

• Some organisms complicate the picture by holding several territories that can be thousands of miles away from each other, and getting to each of them through a process called migration.

Models of Habitat Choice

• Habitat Choice models examine how animals distribute themselves in space and time with respect to some resource in their environment.

• These resources might be food items, mates, refuge from predators, etc.

• What Ethologists look at is the behavioral decisions making (how organisms choose where to live) and how that affects the distribution of animals in time and space.

The IFD Model• It has long been known that animals distribute

themselves in an area around some resource. For example, if one habitat has more food available than another, more animals can be found in the area with more food.

• The Ideal Free Distribution Model (IFD) was developed to look at what behavioral rules animals used to distribute themselves between habitats.

• The IFD model supposes a situation were there is no predation, all food in a given patch is of equal quality, and moving between patches poses no risk. Essentially then, it eliminates all variables except for the one, in particular, that the scientists want to observe.

IFD Model cont’d• Let’s say we have two habitats H1 & H2.• The resources of H1 (R1) provide 5 units of

food/min of search time. The resources of H2 (R2) provide 3 units of food/min of search time.

• We are studying a population of N individuals that can move freely between H1 and H2 with no cost.

• How many individuals should end up at H1 & H2?• The IFD model predicts that the numbers of

individuals in a habitat will stabilize around the number of individuals that would cause a diminishing of resources if one of them moved. Mathematically that is: R1/N1 = R2/N2 (that is when the per capita intake rate of individuals in both patches is equal).

• This is known as the resource matching rule.

More IFD

1. Lets say that 10 individuals settle in H1(N1 = 10). Using the resource matching rule, how many individuals would you expect to settle in H2 (N2 = ?)

2. By extension then what is the maximum population that these two habitats can support?

H1H2

5 units/min

3 units/min

N = individuals entering the area distributing around the food resource of the area

R1R2

Answers• The Resource Matching Rule says that R1/N1 =

R2/N2

• In this case R1 = 5, R2 = 3, and N1 = 10. We are looking for N2.

• 5/10 = 3/N2, cross multiply, 5*N2 = 30, so N2 = 6.• So in this example, H1 can support 10 individuals,

and H2 can support 6 individuals. Between the two habitats 16 individuals can be supported.

IFD and Foraging Success

• Scientists have looked at IFD and many types of resource allocation. Here we will look at two studies centered around foraging choice, looking at two things in particular:

1. Whether animals actually do distribute themselves according to the prediction of the resource matching rule.

2. Whether all individuals receive about the same amount of food, as predicted by the IFD model.

IFD Food Experiment 1

• The first experiment was conducted by Manfred Milinski, in 1979.

• He took a tank which contained 6 Stickleback fish and two feeders that distributed food (one on either side of the tank).

• Milinski looked at two distributions of food 5:1 and 2:1. The stickleback fish distributed themselves accordingly (during the 5:1 test, 5 fish were under the five side and 1 fish was under the one side).

• Supports the matching rule.

IFD Food Experiment 2

• Milinski’s experiment could not measure the individual feeding success of each organism.

• To examine this prediction of the IFD model, we need to look at David Harper’s work with Mallard Ducks.

• Harper worked with Mallards on a pond at Cambridge University, using an experimental design similar to Milinski’s. He had grad students stand at “feeding stations” 20 meters apart and throw pre-cut and weighed pieces of bread into the pond.

• When equal numbers of equal sized bread were thrown by the students, the ducks quickly distributed themselves in a 1:1 ratio.

More on Experiment 2• Additionally, when one of the students threw

twice as much bread, the ducks distributed themselves in a 2:1 ratio.

• During this experiment, the observers noticed that some ducks seemed to be very aggressive and tended to receive a disproportionate amount of food in their area.

• What this means is that while the ducks distributed themselves according to the resource matching rule, all individuals were NOT receiving the same amount of food across the feeding areas (patches).

• So the ducks seem to work according to a modified version of the resource matching rule.

Territoriality• Remember that Territoriality is the occupation

AND DEFENSE if particular areas within a habitat.• Territories can provide their owners with exclusive

access to food, mates, and safe haven from predators, and are typically vigorously defended from intruders.

• Such defense can be costly both in terms of time and energy, representing a cost of territoriality.

• We will look at territoriality of a single individual or family, but it’s important to understand that some territories are defended by groups of unrelated individuals, and this can lead to interesting and dramatic Between-group interactions (ex. Raiding parties of Chimpanzees, etc.)

Territoriality and Learning

• Most models of territoriality assume that animals are capable of assessing the quality of resources in a potential territory.

• These models generally ignore how learning affects the establishment and maintenance of a territory.

• These learning-based models have been constructed; however, and we will look at two of them where learning affects decisions regarding both the acquisition and subsequent maintenance of territories.

Territoriality in Juvenile Lizards

• Judy Stamps made an in-depth analysis of territoriality in juvenile Anolis aeneus lizards.

• These lizards form territories early in life.• Stamps was interested in where and how

juveniles decided to stake out territories.• She started by looking at the importance of food

availability in structuring territoriality, but despite repeated tries, she was unable to come up with a definitive connection between food availability and territoriality.

• Rather she found over time that safety from predation, and suitable temperature appeared to be the most important attributes of a desirable territory in the Anole lizards she studied.

More Anole Territoriality

• …but how did the juvenile lizards determine which territories were suitable with respect to temperature and predation pressure?

• Do these lizards learn which territories are best from the behavior of other lizards?

• She noticed that juvenile lizards seemed interested in what other lizards were doing and wondered if they could share information about what makes a good territory (this is known as conspecific cueing).

• So, here is how Stamps tested the concept of conspecific cueing in her lizards:

Conspecific Cueing Lizard

Experiment• Stamps showed a juvenile lizard two very similar

territories, one which was vacant, and one that had an A. aeneus lizard occupant.

• Then she gave that lizard the chance to occupy either of the territories she had originally showed it (minus the lizard who had been living there).

• In almost all cases the lizard chose to live in the territory that had previously been lived in.

• Additionally, if she showed the lizard two vacant territories, there was an equal probability that it would inhabit either territory when given the chance.

• Stamps determined that there was a strong visual component to conspecific cueing in A. aeneus.

Anolis aeneus

Territory Owners and Satellites

• Territoriality often requires constant vigilance against both predators and conspecific intruders who might attempt to make that territory their own.

• The second experiment we will discuss, looked at the complex relationship between vigilance and territoriality in Pied Wagtails, by seeing if it is ever in the bird’s best interest to share it’s territory.

Pied Wagtail (Motacilla alba)

Pied Wagtail Territoriality

• From the perspective of a territory holder, intruders need not always be a liability.

• During the winter, Pied Wagtails defend territories along riverbanks were they eat insects that have washed ashore.

• This resource is “renewable” in the sense that there are always more insects washing up on shore.

• So what this means is that if the Wagtail times things correctly, it can eat an insect in part of it’s territory, and by the time it finishes patrolling the rest of its territory and gets back to that place, there should be another insect for it to eat.

More on wintering Wagtails

• Nick Davies and Alasdair Houston tracked the movements of Pied Wagtails long the Thames River.

• They found that the birds systematically searched there territory and timed their rounds so that they did not return to an area where they had foraged until sufficient time had passed for a new crop of insects to have washed ashore.

• In the winter months, the Wagtails often had to deal with territorial intruders.

• Under certain conditions intruders are tolerated (and then referred to as satellites), but under other conditions intruders are aggressively chased off the territory.

• Davies and Houston wanted to know why…

Satellites are helpful• A territory is worth more to its owner than to an

intruder (the owner knows more about the territory than the intruder does).

• If an owner lets an intruder become a satellite, it gains a “partner” in territorial defense, but looses some foraging related benefits.

• Davies and Houston built a mathematical model to predict when owners would allow satellites on their territories and when they would not.

• It boils down to this: When food is plentiful, intruders are tolerated. When food is scarce, intruders are shooed of. The intruders (with no food source of their own) are always willing to share the cost of territory defense for food, but the owners are not always willing to allow it.

How to keep a territory in the

family

• Florida Scrub Jays have an elaborate system of familial “helpers-at-the-nest” and as a result a territorial inheritance system whereby territory ownership is passed down across generations leading to family dynasties.

• Each territory starts with a monogamous pair, and up to 6 helpers-at-the-nest. All help in territorial defense.

• Generally territories start small but expand (as the family does) through a process known as territorial budding.

• At about 2.5 years of age, a male scrub jay (with family help) will expand the boundaries of the family territory, and defend his new “budded” territory.

Migration• Migration is seen across many species of animals.• In some species, annual migration is obligatory,

occurring like clockwork.• In some species, migration only occurs when

conditions become poor. This is known as interruptive migration.

• In some species, only a portion of the population migrates, while the rest of the population stays put.

• This begs many questions by scientists: how do they know where to go, how do they know when to go, how do they know how to go, how do they prepare to go, etc.

Migration and Navigation

• The various migratory animal species have evolved the ability to use various cues to navigate their migratory courses:o The position of the suno The position of the starso Various landmarks on the groundo The smell of a particular streamo The magnetic field of the eartho Etc.

• The bottom line is that migrating animals must determine if they are heading where they want to go, and if not, how they can get back on track.

• Because the sun is such a large, prominent object in the sky, and because it provides information about direction, ethologists have long suspected that migrating animals might use the sun to help them navigate.

The Sun Compass• Background about the Monarch Butterfly

migration.o Tens of millions of Monarch Butterflies migrate to central Mexico each

year.o Limbs of trees have been known to snap with the weight of too many

butterflies.o They travel up to 6000 miles on their migratory tripo They almost never get lost while migrating, even on their first trip.

• On their migration southward, the Monarch’s use the position of the sun, in relation to the time of day to help them navigate.

• Sarah Perez wanted to test this, so they conducted a classic “clock-shift” experiment.

• Perez and her team raised two populations of Monarch butterflies. The control group was raised in a room where the day and night matched what was occurring naturally outside.

Perez study cont’d• For the experimental population, they slowly

shifted the light-dark cycle for the Monarchs back 6 hours. So for example if it was noon at the lab, the control butterflies thought it was but, and the experimental butterflies thought it was 6:00pm.

• During the autumn migration period Perez and her study team released the butterflies and kept track of the direction the populations of butterflies few using hand-held compasses.

• The control group flew directly south, the same as wild populations.

• The experimental group flew due west (just as Perez and her team had predicted), because they were using the sun compass to help them navigate.

More Perez study• The 6 hour shift in time caused the butterflies to

misinterpret the information that the sun was conveying about direction, and fly west instead of south.

• Perez and her team only followed the released butterflies for 5 minutes.

• Henrik Mouritsen and Barrie Frost repeated the Perez experiment but built flight simulators that allowed them to measure the direction of flight of a tethered butterfly for extended periods.

• Mouritsen and Frost confirmed the results of the Perez study and the fact that Monarch Butterflies use the position of the sun with respect to time as a navigational aid for migration.

Indigo Buntings & Stars

• The vast majority of passerine birds migrate at night, which prohibits them from using the sun as a navigational aid.

• Steven Emlen did a study using Indigo Buntings that showed they used stars as a navigational aid on their yearly 2000 mile migration from the North Eastern United States to the Bahamas, Mexico and Panama.

Emlen’s Star Experiment

• Emlen put buntings in special cages that clearly marked the direction they would like to fly, and exposed them to the sky at night.

• On clear nights they all made starts at flying either south (in the fall) or north (in the spring). On cloudy nights there was no clear preference in flight direction.

• Emlen repeated the experiment in a planetarium where he could control the position of the stars, and showed that the buntings in fact were keying in on the geometric patterns of the northern constellations. Removing one star from the constellation did NOT impede their navigational progress. (why would that be an ESS?)

The Earth’s Magnetic Field

• This effect has long been suspected, but the first scientific test of it was in the 1960’s and 70’s when small magnets glued to the back of pigeons disoriented the birds flying across a 15-30 mile route.

• Evidence of the earth’s magnetic field being used in navigation has been found in a wide diversity of animals, including: birds, amphibians, reptiles, and insects.

• Bobolinks have one of the longest round-trip annual migrations of any animal (12,400 miles). They spend the summer months in Canada and the Northern US, before migrating to South America (primarily Brazil, Paraguay, and Argentina).

Bobolink (Dolichonyx

oryzivorus)

Bobolink Navigation• Robert Beason and Joan Nichols wanted to find

out if Bobolinks used the earth’s magnetic field during their epic migration.

• To do this Beason and Nichols emulated Steven Emlen’s planetarium study, with one exception, they also introduced instrumentation that could alter the magnetic field in the planetarium.

• When the stars and the magnetic field were properly aligned, the birds wanted to fly south (as predicted and as wild birds would do).

• When the stars were aligned properly, but the magnetic field was reversed, the birds were confused and followed magnetic south rather than follow the stars.

Heritability of Migratory

Restlessness• This is a look at whether the timing of the start of

a Migration is genetic in origin, and thus capable of being inherited.

• Francisco Pulido and his colleagues designed an experiment to test this using the German blackcap bird (Sylvia atricapilla).

Migratory Restlessness cont’d

• Pulido brought wild blackcaps into the laboratory and measured their migratory restlessless.

• They took the 10 birds with the latest onset of migratory restlessness, and allowed them to mate.

• They produced a total of 26 offspring. Of these, 4 breeding pairs (with late onset migratory restlessness) were selected and again allowed to breed, producing 14 total second generation offspring in a line selected for late migratory onset.

• In only two generations, migratory restlessness was delayed for an average of 7.65 days.

• This led Pulido and his colleagues to believe that variance in migratory patterns may indeed be due to genetic variance.