chapter 8: choosing where to live habitat selection: choosing an appropriate place to breed or...

Chapter 8: Choosing where to liveChapter 8: Choosing where to live

Habitat Selection: Choosing an Habitat Selection: Choosing an appropriate place to breed or overwinter is appropriate place to breed or overwinter is an essential decision for most organisms.an essential decision for most organisms.

Although many organisms can succeed in Although many organisms can succeed in a variety of habitats, there is usually a a variety of habitats, there is usually a preferred habitat where the organism does preferred habitat where the organism does best.best.

Habitat ChoiceHabitat Choice

For example, Great Tits nest in both mixed For example, Great Tits nest in both mixed woodlands and hedgerows but will move woodlands and hedgerows but will move into empty territories in mixed woodland if into empty territories in mixed woodland if they become available. This suggests that they become available. This suggests that mixed woodland is the preferred habitat. mixed woodland is the preferred habitat.

In fact, Great Tits do reproduce more In fact, Great Tits do reproduce more successfully in mixed woodlands.successfully in mixed woodlands.

Competition between individuals for territories Competition between individuals for territories often results in the better competitors settling in often results in the better competitors settling in sourcesource habitats and the remainder in habitats and the remainder in sinksink habitats.habitats.

Source habitats: reproductive success produces Source habitats: reproductive success produces an excess of offspring. an excess of offspring.

Sink habitats: reproductive success is not Sink habitats: reproductive success is not enough to sustain the population and immigrants enough to sustain the population and immigrants are necessary to maintain population size.are necessary to maintain population size.

Understanding source-sink dynamics has Understanding source-sink dynamics has been a major focus of conservation been a major focus of conservation biology in recent years as has the whole biology in recent years as has the whole topic of habitat loss because many habitat topic of habitat loss because many habitat specialists depend completely on certain specialists depend completely on certain limited and/or high demand sites (e.g. limited and/or high demand sites (e.g. wetlands and sandy beaches).wetlands and sandy beaches).

Habitat evaluation in side-blotched Habitat evaluation in side-blotched lizardslizards

In some cases of territorial competition In some cases of territorial competition evenly matched individuals evaluate evenly matched individuals evaluate habitat quality and adjust territorial habitat quality and adjust territorial boundaries accordingly.boundaries accordingly.

Male side-blotched lizards defend Male side-blotched lizards defend territories that contain rocks females use territories that contain rocks females use for basking and cover.for basking and cover.


Males defend territories that contain rocks Males defend territories that contain rocks to attract females. to attract females.

When researchers removed rocks from When researchers removed rocks from some territories and added them to others some territories and added them to others the lizards responded by adjusting territory the lizards responded by adjusting territory boundaries.boundaries.


Males who had lost rocks expanded their Males who had lost rocks expanded their territories, males who gained rocks lost territories, males who gained rocks lost ground.ground.

End result was that territories that each End result was that territories that each attracted one female were established.attracted one female were established.

Honey bee habitat evaluationHoney bee habitat evaluation

When honeybee colonies split half of the When honeybee colonies split half of the bees and the old queen depart and settle bees and the old queen depart and settle in a tree for several days.in a tree for several days.

During this period workers scout for new During this period workers scout for new potential hive chambers in hollow trees, potential hive chambers in hollow trees, cliffs and holes.cliffs and holes.


Sites 30-60 liters in volume cause scouts Sites 30-60 liters in volume cause scouts to dance back at the swarm.to dance back at the swarm.

Dancing encourages other bees to visit the Dancing encourages other bees to visit the potential sites.potential sites.

These bees, if they find the site attractive, These bees, if they find the site attractive, may also dance when they return to the may also dance when they return to the swarm.swarm.


Scout bees visit a site only a few times Scout bees visit a site only a few times and each time dance less vigorously than and each time dance less vigorously than before.before.


Consequently, if a site is to remain in Consequently, if a site is to remain in contention it must be attractive enough contention it must be attractive enough that the rate of recruitment of new scouts that the rate of recruitment of new scouts exceeds the drop out rate of old scouts.exceeds the drop out rate of old scouts.

Sites that fail to attract new scouts drop Sites that fail to attract new scouts drop out of contention.out of contention.


At some point many or all scouts are At some point many or all scouts are advertising and visiting the same location. advertising and visiting the same location.

As a result of encountering many other As a result of encountering many other scouts at a potential hive site some bees scouts at a potential hive site some bees may begin “piping” giving a vibrational may begin “piping” giving a vibrational signal to the swarm.signal to the swarm.

If enough scouts give this signal all bees in If enough scouts give this signal all bees in the swarm begin to shiver to warm up and the swarm begin to shiver to warm up and then fly to the new site.then fly to the new site.


Interestingly, when offered a choice of Interestingly, when offered a choice of equally suitable sites, but differing in their equally suitable sites, but differing in their distance from the source hive, bees distance from the source hive, bees generally prefer the more distant site even generally prefer the more distant site even though the queen is a poor flier.though the queen is a poor flier.


Choosing the more distant site reduces Choosing the more distant site reduces competition with the original hive.competition with the original hive.

Consistent with this competition Consistent with this competition hypothesis, northern European colonies hypothesis, northern European colonies (which are larger than those in the south) (which are larger than those in the south) move further when establishing new move further when establishing new colonies.colonies.

Habitat preferences of territorial Habitat preferences of territorial aphids.aphids.

Female aphids on cottonwood trees hatch Female aphids on cottonwood trees hatch in spring and attempt to secure a leaf on in spring and attempt to secure a leaf on which to form a gall in which to reproduce.which to form a gall in which to reproduce.

Females choose large leaves and induce Females choose large leaves and induce gall formation on the midrib.gall formation on the midrib.


Females often encounter competitors and Females often encounter competitors and fight for as long as two days (and often fight for as long as two days (and often die) trying to secure a territory.die) trying to secure a territory.


8.7


Defeated or small females are forced to Defeated or small females are forced to accept inferior habitats and choose either accept inferior habitats and choose either small unoccupied leaves or settle on large small unoccupied leaves or settle on large leaves that already have a gall, but further leaves that already have a gall, but further along the midrib, where there are fewer along the midrib, where there are fewer nutrients.nutrients.

As expected, solo occupancy of a small As expected, solo occupancy of a small leaf and sharing a larger leaf have equal leaf and sharing a larger leaf have equal payoffs.payoffs.

Costs and benefits of territorialityCosts and benefits of territoriality

Territoriality is widespread, but not all Territoriality is widespread, but not all organisms defend territories.organisms defend territories.

Why do some do so, but not others?Why do some do so, but not others?


Benefit of territoriality is exclusive control of its Benefit of territoriality is exclusive control of its contents and the females that these may attract.contents and the females that these may attract.

However, costs of territorial defense can be However, costs of territorial defense can be considerable.considerable.

Defense requires time and effort. E.g. territorial Defense requires time and effort. E.g. territorial surgeonfish on coral reefs may have to chase a surgeonfish on coral reefs may have to chase a rival off its territory on average more than once rival off its territory on average more than once every minute!every minute!


Energetic costs of territorial defense may be Energetic costs of territorial defense may be enough to reduce lifespan.enough to reduce lifespan.

Male Yarrow’s spiny lizards given testosterone Male Yarrow’s spiny lizards given testosterone implants spent more time defending their implants spent more time defending their territories than non-implanted males. territories than non-implanted males.

Experimental males not given food supplements Experimental males not given food supplements died at higher rates than control and food-died at higher rates than control and food-supplemented males, which suggests mortality supplemented males, which suggests mortality was due to high energetic costs.was due to high energetic costs.


As well as risks of injury and exhaustion, there As well as risks of injury and exhaustion, there are indirect costs of elevated testosterone are indirect costs of elevated testosterone levels. High levels may reduce immune function levels. High levels may reduce immune function and also make the organisms more vulnerable to and also make the organisms more vulnerable to predators.predators.

Different forms of the lizard Different forms of the lizard UtaUta stansburiana stansburiana have different levels of circulating testosterone have different levels of circulating testosterone and the form with the highest levels has the and the form with the highest levels has the lowest annual survival rates.lowest annual survival rates.

Because territoriality is costly we expect it Because territoriality is costly we expect it to be maintained only when it pays. to be maintained only when it pays.

Thus, territories may be only intermittently Thus, territories may be only intermittently defended.defended.

E.g. pseudoscorpions colonize dead or E.g. pseudoscorpions colonize dead or dying trees dispersing once every several dying trees dispersing once every several generations by hitching a ride under the generations by hitching a ride under the wing covers of large beetles!wing covers of large beetles!

Only when riding on beetles are territories Only when riding on beetles are territories small enough that the costs of defense are small enough that the costs of defense are low enough to make it worthwhile for low enough to make it worthwhile for males to defend them. males to defend them.

Patterns of distributionPatterns of distribution

Depending on whether there are Depending on whether there are differences between individuals in their differences between individuals in their ability to defend resources we may get ability to defend resources we may get one of two possible distributions of one of two possible distributions of foragers among sites.foragers among sites.

Ideal free distributionIdeal free distribution

Ideal free distributionIdeal free distribution: in an ideal free : in an ideal free distribution organisms distribute distribution organisms distribute themselves among sites so that average themselves among sites so that average payoffs are the same at each site.payoffs are the same at each site.

I.e. more valuable sites attract more I.e. more valuable sites attract more settlers so that the average payoff is settlers so that the average payoff is reduced to equal that of a less inherently reduced to equal that of a less inherently valuable site.valuable site.

Ideal despotic distributionIdeal despotic distribution Ideal despotic distributionIdeal despotic distribution: in this case some : in this case some

individuals are competitively superior and can individuals are competitively superior and can exclude other individuals from an area. exclude other individuals from an area.

For, example among wintering American For, example among wintering American redstarts in Jamaica older males occupy redstarts in Jamaica older males occupy territories in Black Mangrove forest, the best territories in Black Mangrove forest, the best habitat, and most females and younger males habitat, and most females and younger males are compelled to use second growth scrub, are compelled to use second growth scrub, which is of lower quality.which is of lower quality.

Overwintering redstartsOverwintering redstarts

Birds using Black Mangrove forests Birds using Black Mangrove forests maintain their weight over winter, but birds maintain their weight over winter, but birds in second growth scrub generally lose in second growth scrub generally lose weight.weight.

Overwintering redstartsOverwintering redstarts

The extra bodyweight of older males allows The extra bodyweight of older males allows them to depart to their breeding grounds earlier them to depart to their breeding grounds earlier in the spring, which is a big advantage because in the spring, which is a big advantage because early arriving males obtain the best breeding early arriving males obtain the best breeding territories.territories.

Females that can secure high quality winter Females that can secure high quality winter territories also benefit by being able to depart territories also benefit by being able to depart early as they have a longer period in which to early as they have a longer period in which to raise young.raise young.

Territorial contestsTerritorial contests

Studies of territorial defense show that the Studies of territorial defense show that the resident almost always wins in an resident almost always wins in an interaction with an intruder.interaction with an intruder.

A variety of potential explanations have A variety of potential explanations have been advanced to explain this pattern. been advanced to explain this pattern.

ESS explanationESS explanation

One explanation put forward is a game One explanation put forward is a game theory explanation that animals may play theory explanation that animals may play an evolutionarily stable strategy in which an evolutionarily stable strategy in which they apply an arbitrary rule “resident they apply an arbitrary rule “resident always wins.”always wins.”

Not been possible to show that such a rule Not been possible to show that such a rule applies in any species. applies in any species.

Speckled wood butterfliesSpeckled wood butterflies

One species in which rule was believed to One species in which rule was believed to apply was speckled wood butterfly.apply was speckled wood butterfly.

Males defend sunspots against other Males defend sunspots against other males. Resident males trapped in a males. Resident males trapped in a butterfly net and then released from the butterfly net and then released from the net back at their territory where a new net back at their territory where a new male had established itself almost always male had established itself almost always retreated from the new resident male.retreated from the new resident male.

Speckled wood butterfliesSpeckled wood butterflies

However, when work was repeated However, when work was repeated without the stress of holding males in a without the stress of holding males in a butterfly net, the original resident evicted butterfly net, the original resident evicted the intruder in 50 of 52 instances.the intruder in 50 of 52 instances.

Appears that in the first study the original Appears that in the first study the original resident males were so affected by the net resident males were so affected by the net that they simply tried to escape.that they simply tried to escape.

Resource holding powerResource holding power

An obvious alternative explanation for why An obvious alternative explanation for why residents usually win is that they have residents usually win is that they have more resource holding power (they are more resource holding power (they are e.g. larger, stronger, more aggressive than e.g. larger, stronger, more aggressive than intruders).intruders).

Contests among dragonfliesContests among dragonflies

For example male damselflies engage in For example male damselflies engage in long chases with other males when long chases with other males when fighting over territories.fighting over territories.

In these interactions size fat reserves are In these interactions size fat reserves are the factor that determines who wins. the factor that determines who wins. Males with larger fat reserves afford to Males with larger fat reserves afford to contest a war of attrition for longer.contest a war of attrition for longer.

Residents have more to lose then Residents have more to lose then intrudersintruders

Differences in resource holding power do Differences in resource holding power do not always explain who wins in a dispute.not always explain who wins in a dispute.

In many cases older individuals fight In many cases older individuals fight harder and are more willing to persist in a harder and are more willing to persist in a dispute than younger individuals. dispute than younger individuals.


For example, as eggfly butterflies age they For example, as eggfly butterflies age they become increasingly persistent in become increasingly persistent in aggressive interactions and fight harder.aggressive interactions and fight harder.


Third hypothesis for why residents usually Third hypothesis for why residents usually win is that residents have more to fight for win is that residents have more to fight for than intruders.than intruders.

Fitness payoffs for residents on a territory Fitness payoffs for residents on a territory often increase with time and their chances often increase with time and their chances of securing another territory decline. of securing another territory decline. Thus, residents may be willing to fight Thus, residents may be willing to fight much more to keep what they have.much more to keep what they have.


One way in which fitness benefits can increase One way in which fitness benefits can increase for a territory holder over time is that after an for a territory holder over time is that after an initial period of intense interaction with neighbors initial period of intense interaction with neighbors to establish boundaries, costs of defense usually to establish boundaries, costs of defense usually decline.decline.

For example, in one African lizard, residents For example, in one African lizard, residents allow familiar neighbors to approach closer and allow familiar neighbors to approach closer and chase them shorter distances than they chase chase them shorter distances than they chase strangers.strangers.


The “dear enemy” hypothesis suggests The “dear enemy” hypothesis suggests that residents may have an interest in that residents may have an interest in maintaining a stable set of neighbors maintaining a stable set of neighbors because of the reduced defense costs.because of the reduced defense costs.

Consistent with this sometimes pairs of Consistent with this sometimes pairs of neighbors collaborate to drive off an neighbors collaborate to drive off an intruder.intruder.


Territorial fiddler crabs occasionally assist Territorial fiddler crabs occasionally assist a neighbor in defending their territory a neighbor in defending their territory against an intruder. Usually, the neighbor against an intruder. Usually, the neighbor helps when the intruder is larger than the helps when the intruder is larger than the neighbor but smaller than him.neighbor but smaller than him.

Assistance helps and pairs win 88% of Assistance helps and pairs win 88% of interactions while unassisted residents win interactions while unassisted residents win only 71% of the time.only 71% of the time.


Dear enemy effect contributes to asymmetry in Dear enemy effect contributes to asymmetry in what resident has to lose and what intruder has what resident has to lose and what intruder has to gain.to gain.

This asymmetry suggests that in replacement This asymmetry suggests that in replacement experiments the longer the new resident has experiments the longer the new resident has been in place before the original resident is been in place before the original resident is released to challenge him the more likely the released to challenge him the more likely the contest will be prolonged.contest will be prolonged.


This hypothesis supported in numerous This hypothesis supported in numerous studies.studies.

E.g. in tarantula wasps a resident removed E.g. in tarantula wasps a resident removed and returned only a few minutes after a and returned only a few minutes after a new resident is established evicts the new new resident is established evicts the new resident in about 3 minutes. If the old resident in about 3 minutes. If the old resident is held for an hour, fights last on resident is held for an hour, fights last on average 25 minutes.average 25 minutes.

Costs and benefits of dispersalCosts and benefits of dispersal

Dispersing to seek a new territory involves Dispersing to seek a new territory involves a lot of costs including risk of predation a lot of costs including risk of predation and significant energy costs.and significant energy costs.

Why then do organisms disperse?Why then do organisms disperse?


One major reason is to avoid inbreeding. One major reason is to avoid inbreeding.

Mating with relatives increases the chance Mating with relatives increases the chance of expressing deleterious recessive of expressing deleterious recessive alleles.alleles.

Inbreeding thus is likely to reduce fitness Inbreeding thus is likely to reduce fitness of offspring. of offspring.


For example, inbred oldfield mice are 50% For example, inbred oldfield mice are 50% less likely to survive than outbred mice less likely to survive than outbred mice and reproduce later.and reproduce later.

In general, males disperse further from their In general, males disperse further from their natal area than do females. In some cases natal area than do females. In some cases females remain close to home because they females remain close to home because they gain assistance in rearing young from their gain assistance in rearing young from their relatives.relatives.

Males are often forced out by other males. For Males are often forced out by other males. For example, in lions young males are often chased example, in lions young males are often chased out by dominant when a pride takeover occurs.out by dominant when a pride takeover occurs.

MigrationMigration

Migration is a widespread from of Migration is a widespread from of dispersal. dispersal.

Some insects and mammals migrate, but Some insects and mammals migrate, but the behavior is especially common among the behavior is especially common among birds.birds.

MigrationMigration

About 50% of all North American breeding About 50% of all North American breeding birds are summer visitors from Central and birds are summer visitors from Central and South America.South America.

Distances traveled in migration are Distances traveled in migration are sometimes amazing. Arctic terns migrate sometimes amazing. Arctic terns migrate from high in the northern hemisphere to from high in the northern hemisphere to Antarctica and back!Antarctica and back!

MigrationMigration

Ruby-throated hummingbirds (weight Ruby-throated hummingbirds (weight about 3 grams) fly directly across the Gulf about 3 grams) fly directly across the Gulf of Mexico. Store about 2g of fat for the of Mexico. Store about 2g of fat for the trip.trip.

MigrationMigration

Migratory species appear to have evolved Migratory species appear to have evolved from sedentary species, but how?from sedentary species, but how?

Many species in the tropics engage in Many species in the tropics engage in short-range migrations where they move short-range migrations where they move from breeding grounds to wintering from breeding grounds to wintering grounds that are quite close. grounds that are quite close.

Short-distancemigration of the Three-wattledBellbird

MigrationMigration

Short-range migrants occur in nine Short-range migrants occur in nine Neotropical songbird families and seven of Neotropical songbird families and seven of these families also include long-distance these families also include long-distance migrants. Co-occurrence suggests short-migrants. Co-occurrence suggests short-range migration preceded long-range range migration preceded long-range migration.migration.

MigrationMigration

The thrush genus Catharus includes 12 The thrush genus Catharus includes 12 species, 7 of which are resident in Central species, 7 of which are resident in Central or South America.or South America.

Swainson’s Thrush

MigrationMigration

Long-distance thrush migrants appear to Long-distance thrush migrants appear to be derived from Central American and be derived from Central American and Mexican species.Mexican species.

Phylogenetic analysis suggests that Phylogenetic analysis suggests that migration has evolved three times in the migration has evolved three times in the genus with subtropical or tropical resident genus with subtropical or tropical resident species giving rise to migratory lineages species giving rise to migratory lineages each time. each time.

Costs and benefits of migrationCosts and benefits of migration

Migration has significant costs in risk of Migration has significant costs in risk of mortality and energy. mortality and energy.

Long over water flights may exhaust Long over water flights may exhaust migrants who then drown. Predators also migrants who then drown. Predators also kill large numbers of exhausted migrants.kill large numbers of exhausted migrants.


To maximize their chances of completing a To maximize their chances of completing a flight birds store large quantities of fat as flight birds store large quantities of fat as fuel and then use a variety of energy fuel and then use a variety of energy saving strategies.saving strategies.

For example, they wait to migrate until For example, they wait to migrate until there are tailwinds, which increase their there are tailwinds, which increase their groundspeed and reduce costs of travel.groundspeed and reduce costs of travel.


Many birds (such as raptors, cranes and Many birds (such as raptors, cranes and storks) make use of soaring and gliding storks) make use of soaring and gliding flight, which is energy efficient, but these flight, which is energy efficient, but these birds cannot cross large bodies of water birds cannot cross large bodies of water because there is no rising warm air, which because there is no rising warm air, which provides lift, over water.provides lift, over water.


Birds also save energy by flying in Birds also save energy by flying in formation because doing so enables birds formation because doing so enables birds to benefit from lift provided by nearby to benefit from lift provided by nearby birds.birds.

Pelicans flying in formation reduce their Pelicans flying in formation reduce their energy expenditure by 11-14%. energy expenditure by 11-14%.


Many birds also minimize risk by avoiding Many birds also minimize risk by avoiding long-distance water crossings. Thus, most long-distance water crossings. Thus, most European migrants cross the European migrants cross the Mediterranean Sea at its narrowest points Mediterranean Sea at its narrowest points either at Gibralter or the Bosphorus in either at Gibralter or the Bosphorus in Turkey.Turkey.


Individual birds also take into account their Individual birds also take into account their condition when deciding whether to make a condition when deciding whether to make a crossing or not.crossing or not.

Red-eyed Vireos captured and weighed at Red-eyed Vireos captured and weighed at stopover sites on the Alabama coast en route to stopover sites on the Alabama coast en route to wintering grounds in the Yucatan Peninsula and wintering grounds in the Yucatan Peninsula and Central America differ in their migratory Central America differ in their migratory orientation depending on their condition.orientation depending on their condition.


Birds with low fat reserves orient Birds with low fat reserves orient westwards avoiding the shorter but riskier westwards avoiding the shorter but riskier oversea crossing. In contrast birds in oversea crossing. In contrast birds in good condition orient south.good condition orient south.


One of the most striking migratory flights is One of the most striking migratory flights is that of the Blackpoll Warbler, which flies that of the Blackpoll Warbler, which flies directly from the coasts of the northeastern directly from the coasts of the northeastern U.S. and Canada out over the Atlantic U.S. and Canada out over the Atlantic directly to northern South America a directly to northern South America a 3,000km flight.3,000km flight.


Blackpoll’s trip requires 50-90 hours of Blackpoll’s trip requires 50-90 hours of continuous flight, but many birds make it in good continuous flight, but many birds make it in good condition.condition.

The warblers make good use of winds to help The warblers make good use of winds to help them on their way. They depart only when a them on their way. They depart only when a west to east cold front can push them out over west to east cold front can push them out over the Atlantic so that they can later pick up the the Atlantic so that they can later pick up the prevailing westerly winds over the Atlantic to prevailing westerly winds over the Atlantic to push them towards their destination.push them towards their destination.


In the spring, blackpolls do not migrate In the spring, blackpolls do not migrate over the long sea route, but mainly travel over the long sea route, but mainly travel over land. over land.

Why?Why?


Traveling over land makes more sense Traveling over land makes more sense because the prevailing winds would be because the prevailing winds would be against them over the sea.against them over the sea.


The main benefit of migration for most The main benefit of migration for most species is that it allows organisms to species is that it allows organisms to exploit seasonally abundant food supplies.exploit seasonally abundant food supplies.

By moving north to breed during the long By moving north to breed during the long days of the northern summer, birds have days of the northern summer, birds have more time to gather food for their young more time to gather food for their young and food is also abundant.and food is also abundant.


Resources other than food are also Resources other than food are also important in other cases. important in other cases.

For example, the mass migration of For example, the mass migration of wildebeest on the Serengeti Plain of East wildebeest on the Serengeti Plain of East Africa appears to be driven largely by Africa appears to be driven largely by diminishing supplies of water.diminishing supplies of water.


For Monarch butterflies which migrate to For Monarch butterflies which migrate to Mexico to winter in a handful of high Mexico to winter in a handful of high valleys the attraction is sheltered roosting valleys the attraction is sheltered roosting spots.spots.

Killing freezes are rare in the wooded Killing freezes are rare in the wooded mountains where Monarchs winter. Moist mountains where Monarchs winter. Moist cool conditions on mountains suit cool conditions on mountains suit Monarchs.Monarchs.


Logging of sites is having a severe effect Logging of sites is having a severe effect on the quality of the habitat as a roosting on the quality of the habitat as a roosting site for Monarchs.site for Monarchs.

Opening of canopy even with only partial Opening of canopy even with only partial cutting increases likelihood of Monarchs cutting increases likelihood of Monarchs becoming wet and then freezing, becoming wet and then freezing, especially when there is increased especially when there is increased exposure to open sky.exposure to open sky.

chapter 8: choosing where to live habitat selection: choosing an appropriate place to breed or...

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preferred habitat

habitat specialists

habitat quality

habitat choice

habitat selection

topic of habitat loss

new scouts

blotched lizards males