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大學部 生態學與保育生物學學程 (必選)
2010 年 秋冬
空間分佈 (spatial distribution)
─動物行為學 (Ethology)
鄭先祐(Ayo)
國立 臺南大學 環境與生態學院
生態科學與技術學系 教授
Ayo NUTN Web: http://myweb.nutn.edu.tw/~hycheng/
10 空間分佈 (Spatial distribution)
 Remaining at home versus leaving
 Habitat selection (棲地選擇)
 Migration (遷徙)
Ayo 教材 (動物行為學 2010)
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Introduction to animal movement
 Nearly all of the 25 species of sturgeons (鱘魚) are
endangered
 Chinese sturgeon can reach 4 or 5 m in length, weigh
more than 550 kg (1,000 lbs.), and live for a century


It is anadromous, spending most of its life in the sea
But returning to freshwater to breed
Anadromous 由海移棲淡水河產卵的
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Humans have disrupted sturgeon spawning
 Historically, Chinese sturgeon spawned upstream in
the Yangtze River

Taking 18 months to migrate 3,000 km to their
spawning grounds
 The Gezhouba Dam blocked Chinese sturgeon from
their migration route

They bred below the dam
 The number of spawning adults plummeted
 Disruption by the dam, water pollution, overfishing,
and heavy boat traffic
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Dispersal and philopatry
 Natal dispersal: movement between the natal area or
social group and the area or social group where breeding
takes place


Animals are born in one place and move to another to breed
They don’t return to their birthplace
 Breeding (post-breeding) dispersal: movement between
two successive breeding areas or social groups

Occurs after reproduction
 Natal philopatry: offspring remain at their natal area and
share the home range or territory with their parents
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Costs of natal philopatry
 Inbreeding: mating between relatives
 Parents and offspring or between siblings
 Inbreeding reduces variation among offspring
Mexican jay
 It is hard to determine the fitness costs of inbreeding
 Because the frequency of inbreeding is usually low
 Mexican jays have fitness costs associated with
inbreeding


Smaller brood sizes, suggesting hatching failure
Fewer of the inbred nestlings survived to the next year
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Other costs of natal philopatry
 Reproductive suppression: adult breeders suppress
reproductive development of young through chemical
means (e.g., pheromones) or behavioral methods (e.g.,
aggression)


Suppressed young may not reproduce
Their genes are represented by helping rear other young
 Young compete with relatives for food, nest sites, or
mates
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Benefits associated with philopatry
 Populations become adapted to local conditions
 Genes that work well under local conditions are
favored by selection
 An animal that disperses may not be as well adapted to
its new home
 Familiarity with the local physical and social setting
 Young are efficient at finding and controlling food and
escaping from predators
 Reduced levels of aggression and stress associated
with social interactions
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Another benefit of philopatry
 Philopatric young may live longer and leave more
offspring

Because of the low risks and energy use associated with
living in familiar surroundings
 Offspring may remain at home due to constraints
 A shortage of potential mates
 A lack of suitable territories to settle in
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Costs of natal dispersal
 Dispersers face high energy costs and increased
predation risk


Small mammals in underground burrows have a
constant physical environment and safety from
predators (hawks and owls)
Long-distance above-ground dispersal exposes them to
harsh weather conditions and predators
 Other costs: a lack of familiarity with the terrain
 High levels of aggression from residents in the new
area
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Animals in new homes face challenges
 Male prairie voles released at unfamiliar locations
move greater distances

And take longer to find refuge than those released at
familiar locations
 In woodland voles and Norway rats, nonresidents
face harsh treatment by residents


Dispersal-induced mortality can exceed 50%
But dispersal costs can be negligible in some species
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Benefits of natal dispersal: avoiding competition
 Dispersers avoid competition with kin for critical
resources
 Wolf spider mothers help their offspring disperse



Young climb onto their mother’s abdomen
Spiderlings face kin competition if they all left their
mother’s abdomen in the same location
They do not simultaneously disperse from mom’s
abdomen
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 Patterns of natal dispersal and maternal movement in wolk
spiders ensure that siblings do not compete with one another.
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Not all species avoid competition through
dispersal
 In other species, avoiding competition with kin cannot
explain patterns of natal dispersal
 If competition for resources leads to dispersal, dispersal
would increase with increases in litter size

In brown bears and prairie voles natal dispersal is not
associated with litter size
 Natal dispersal is more common in small groups of
prairie voles

Avoidance of competition for resources at home is not an
important function of natal dispersal in this species
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Benefits of natal dispersal:
avoiding inbreeding
 Some young leave home to avoid breeding with close
relatives


Young disperse in the presence of an opposite-sex
parent
All members of one sex may disperse, no matter what
the ecological or social conditions
 In Belding’s ground squirrels, all males leave home
 Regardless of the competition for mates or resources
 Nearly all male brown bears leave home regardless of
ecological factors (i.e. population density and sex ratio)
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Inbreeding may or may not be important
 Some scientists argue that it plays a significant role in
dispersal

Others argue that animals rely on mate choice rather than a
risky behavior like dispersal to avoid inbreeding
 Young female mammals avoid selecting their brothers as
mates



In response, their brothers disperse from the natal site to
find females willing to mate with them
So, individuals do not disperse from home to avoid breeding
with relatives
Instead, natal dispersal is the result of females not choosing
male relatives as mates
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 ← brown bears
 ↑Belding’s
 spotted
ground squirrels
hyenas →
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Female mate choice can drive natal dispersal
 Female spotted hyenas rarely disperse from the natal
clan. Most, but not all, males leave their natal clan
 Four hypotheses examine natal dispersal by males




1) competition with other males for mates
2) breeding with close female relatives
3) competition for food resources
4) males disperse in response to patterns of mate
choice by females
 Competition for mates, inbreeding avoidance, and
competition for food do not cause natal dispersal by
males
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Female avoid mating with close relatives
 Female hyenas follow this rule:
 “Avoid mating with males that were members of your
clan when you were born and select as mates those
males that arrived in your clan (through birth or
immigration) after your birth”
 Reducing the chances that females mate with their
father and older brothers
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Another aspect of female choice
 Young females select males with short residency times
in their clan
 Males begin their reproductive career in the clan (natal
or otherwise) that had the most young females


Females choose them as mates
Resulting in long-term fitness benefits for the males
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Proximate causes of natal dispersal
 Ultimate causes of natal dispersal: avoidance of
inbreeding and competition with kin for resources or
mates
 Proximate causes also trigger natal dispersal


Sufficient body size or fat reserves, aggression from
other group members, shortage of food, attraction to
opposite sex individuals in other groups, and weaken
social bonds with members of the natal group
Androgens may organize dispersal behavior through
organizational effects of steroid hormones
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Natal dispersal is also linked to
personality (個性)
 Such as “boldness”(大膽的) or exploratory behavior
 Female great tit post-fledging movement distances
correlates with exploratory behavior


This positive correlation does not characterize all
species
In flying squirrels, long distance dispersers explore
less than short distance dispersers
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Sex biases in natal dispersal
 Males and females differ in whether or not they disperse
from their birthplace


In most bird species, females are more likely to disperse
In mammals, males are more likely to disperse than
females
 Hypotheses to explain sex-biased dispersal
 (1) inbreeding avoidance
 (2) local resource competition
 (3) local mate competition
 (4) cooperative behavior among kin
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Sex bias in dispersal is a compromise
 It avoids the genetic costs of inbreeding
 While enjoying the benefits of familiarity with local
physical and social conditions (philopatry)
 But, which sex leaves home and why is the direction of
the bias different in birds and mammals?
 Two explanations suggest the direction of sex bias


The sex most involved in territory acquisition and
defense stays home because it benefits most from
familiarity with the natal territory
The sex that gets first choice of breeding sites remains
in the natal area and the other sex disperses
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Male birds are philopatric
 Most birds are monogamous (they live in male-female
pairs)
 A resource-defense mating system: males compete for
territories that attract females, rather than competing
for females directly

Familiarity with an area is more important to males than
to females so males should be philopatric
 Female birds disperse to avoid the genetic costs of
inbreeding

And to choose territories with the best resources
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Female mammals are philopatric
 Many mammals show mate-defense polygyny: a single
male mammal defends a group of females


Males compete for females rather than territories
Young or subordinate males disperse to increase their
chances of mating
 Female mammals often live in matrilineal social groups
(groups of mothers, daughters, and granddaughters)

The benefits of living with kin are high
 Females benefit most by staying home
 Males disperse to avoid the genetic costs of inbreeding
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Sex-based dispersal
 Female-biased dispersal in birds is linked to resource-
defense mating systems
 Male-biased dispersal in mammals is linked to matedefense mating systems


Some mammals display resource-defense (rather than
mate defense) polygyny
Natal dispersal is female biased, as predicted
 i.e. for sac-winged bats
 But, in European roe deer, dispersal is not female
biased
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 Sac-winged bat (鞘尾蝠科)
 European roe deer
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The sex with the breeding site remains
in the natal area
 This model assumes that philopatry is more desirable
than dispersal
 Mating systems affect dispersal patterns of mammals
indirectly by influencing whether the father will be
present when his daughters are old enough to breed


If he is not, females have first choice of the breeding site,
and they choose to stay at home
If the father is still around when his daughters reach
sexual maturity, he has first choice of the breeding site,
and so females disperse to avoid inbreeding
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A male mammal’s parental role is limited
 Female mammals nurse their young
 Males have little involvement in offspring care
 So, males can avoid long-term pair bonds
 They can wander over large areas
 With intense competition over mates (i.e. elephant seals,
red deer) a male’s opportunity to breed may be limited

He leaves before his daughters are old enough to reproduce
So, daughters don’t have to disperse to avoid inbreeding
 If a male’s reproductive life span is long and he is present
when his daughters are old enough to breed (i.e.
chimpanzees) Females usually disperse
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Another hypothesis for dispersal: local
mate competition
 Competition for mates is intense in polygynous male
mammals

Dispersal should be more common in males
 In monogamous species, competition for mates is more
equal

Males and females should disperse in similar proportions
 Reducing competition for mates can’t explain all sex
differences in natal dispersal


Avoiding inbreeding influences natal dispersal
i.e. females disperse in monogamous bird species
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Kin cooperation hypothesis
 Cooperative behavior contributes to sex biases in
dispersal

If kin exhibit cooperative behavior, it is beneficial to stay
home
 If cooperation benefits one sex more than the other
 The cooperative sex is philopatric
 The other sex disperses to avoid inbreeding
 The magnitude of sex-biased dispersal increases with
increases in social complexity

Dramatic sex differences in natal dispersal characterize
highly social polygynous mammals
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Sex bias in natal dispersal and social
complexity
 There is a relationship between sex-biased dispersal
and social complexity
 In polygynous ground-dwelling sciurids (ground
squirrels, marmots, prairie dogs)



Social structures range from solitary to large social
groups
Male-biased natal dispersal increased with social
complexity
Not from expected decreases in female dispersal
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 ground squirrels
 marmots
 prairie dogs (土撥鼠)
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 In polygynous ground-dwelling sciurids (members of
the squirrel family), the degree of sex bias in natal
dispersal increases with social complexity.
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Understanding natal dispersal: implications
for conservation
 Dispersal affects the genetic structure of populations
 It promotes gene flow within and between populations
 And maintains genetic diversity
 Habitat destruction fragments populations and hinders
dispersal

Areas between habitat fragments are inhospitable
 To conserve threatened populations
 Preserve dispersal corridors(廊道) to connect larger
areas and promote gene flow
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Stop and think
 Natal dispersal and philopatry are measured by
mark and recapture methods

Genetic methods examine how dispersal translates into
gene flow
 What are some potential problems in using mark-
recapture methods to study dispersal?
 How could you know if an animal dispersed or died?
 How could you design a study to minimize this issue?
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 Mark-recapture methods are often used to monitor
natural populations of small mammals.
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Habitat selection
 Animals that disperse from their natal site or breeding
site must select a new location in which to settle
 The process of habitat selection has three phases:



(1) search (animal searches for a new habitat)
(2) settlement (animal arrives in a new habitat and
begins to establish a home range or territory)
(3) residency (animal lives in the new habitat)
 The phases of search and settlement are costly
 The benefits of habitat selection accrue during
residency
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Indicators of habitat quality
 Animals have clear habitat preferences
 Forest buffalos of Africa prefers grassy clearings and
open stands of forest with large trees


Even though clearings are rare
Herd members can maintain visual and physical contact
 When selecting a habitat, animals evaluate
 The presence of resources (e.g., food, nest and rest sites)
 The presence of conspecifics, and heterospecifics
(members of another species)
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 The African Forest
Buffalo (Syncerus
caffer nanus) is usually
weighing 265–565
kilograms (580–1,250
lb), they are reddish
brown in color.
 Its native habitat is the equatorial forest found in
central and western Africa, and its diet consists
primarily of grasses, twigs, and young shoots. African
Forest Buffalo are sought after by hunters for their
meat and horns. In the wild, leopards are its primary
predator.
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How do animals evaluate real estate?
 Young lizards searching for feeding territories spend
only hours evaluating a location


Do not conduct a detailed assessment of prey availability
They assess habitat characteristics (i.e. light intensity
and amount of leaf litter) that correlate with prey
availability
 A disperser evaluates the presence or absence of
conspecifics in the vicinity of a prospective home

By settling in an unoccupied site, it avoids intraspecific
competiton
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Fitness correlates with numbers of conspecifics
 The ideal free distribution: individual fitness declines as
the number of conspecifics increases
 The Allee effect: individual fitness increases with number
of conspecifics at low to moderate densities


Having a few neighbors is beneficial
Enhanced detection of predators or access to mates
 Two explanations for conspecific attraction regarding
habitat selection


1) Allee effect
2) conspecifics indicate habitat quality
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Conspecifics indicate habitat quality
 Juvenile lizards use conspecfic presence as an indirect cue
to habitat quality
 Individuals evaluate characteristics of resident conspecifics


Breeding birds monitor the reproductive success of
conspecifics in their local area
And use this information to decide where to nest during future
breeding efforts
 Public information: information concerning local
conspecifics

Personal information: the bird’s own breeding success also
affects whether it remains at that site or leaves
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The presence of heterospecifics has costs
and benefits
 For an animal considering whether to settle in an area
 Interactions between species that share mutual resources
could be negative due to interspecific competition
 Interactions between heterospecific individuals can be
beneficial

Mixed species flocks of birds experience the benefits of
enhanced food acquisition and antipredator behavior
 The heterospecific attraction hypothesis: individuals
choose habitat patches based on the presence of established
residents of another species
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The heterospecific attraction hypothesis
 Predicts that individuals searching for a new home
display the strongest attraction to heterospecifics


When the benefits of social aggregation outweigh the
costs of competition, and
When the costs of independent sampling of habitats
(evaluating habitat quality on one’s own rather than
using the presence of heterospecifics as a cue) are high
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Testing the heterospecific attraction hypothesis
 Several possible explanations exist for the attraction of
migrant birds of one species to resident birds of other
species



First, residents indicate high quality habitat
Second, migrants may experience food or safety benefits
from grouping with heterospecific residents
Third, using presence of heterospecific residents to
indicate habitat quality may be a fast, accurate method of
habitat assessment
 Residents have all year to assess the quality of habitat
patches
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Resident titmice influence pied
flycatcher presence and fitness
 Titmice and pied flycatchers both nest in cavities and
forage for arboreal arthropods
 Flycatchers are attracted to the vicinity of titmice


Flycatchers arrive earlier on forest patches with more
titmice
They prefer nest boxes placed near an active titmouse
 ← Titmice
 Pied flycatchers →
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The fitness effects of habitat selection
 Brood sizes of flycatchers were larger in patches with
more titmice

Flycatchers breeding closer to titmice had larger nestlings
 Interspecific competition is not the defining interaction
between titmice and flycatchers
 ← Titmice
 Pied flycatchers →
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Two search tactics for selecting habitat
 Comparison (best-of-N
 Sequential search: the
strategy): the animal
visits several areas,
revisits some, and chooses
the highest quality area
animal visits habitats and
selects the best one


An animal accepts or rejects
a location
If rejected, it keeps searching
Both tactics can occur within a single population
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Sequential searches
 Searchers do not return to areas they have already visited
(except by chance)

They may travel long distances before establishing residence
 Decisions by dispersers are influenced by:
 The time available for the search, quality of available
habitats, and how often high quality habitats are encountered
 Dispersers may have an acceptance threshold
 Which declines as the search continues (i.e., an animal may
be selective at the start of the search and less selective later)
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Effects of natal experience
 Experience in the natal environment influences
habitat selection
 Host preferences exhibited by the parasitoid
wasp



A parasitoid: an organism whose offspring
develop on or within a host, eventually killing
the host
The host of a parasitoid is the equivalent of a
habitat
Female parasitoids select hosts on (or within)
which their offspring will develop
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Host preference in parasitoid wasps
 Female wasps reared on fruit flies preferred fruit flies as
hosts

But only when allowed to gain experience attacking them
 Cues from the natal host prime females to respond to
these cues if encountered again

When re-encountered, the cues are learned by females,
establishing host preference
 The natal environment (here, the natal host) influences
selection of a site for reproduction
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The natal habitat preference induction
 NHPI: An animal’s experience in its natal habitat
induces a preference for a post-dispersal habitat with
similar qualities

The search phase of habitat selection is costly in time,
energy and predation risk
 NHPI helps a disperser to more quickly and efficiently
recognize a suitable habitat

Minimizing the costs of the search phase
 A habitat similar to the one in which the disperser
grew up would be of sufficient quality to settle in

Because the individual has survived to leave home
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Another explanation for NHPI
 Dispersers have greater fitness if they settle in a habitat
similar to their natal habitat

Because their particular phenotype has been shaped by
this type of habitat
 While living at home, individuals develop specific
methods for finding and capturing prey

These methods might work best in post-dispersal habitats
similar to their natal habitat
 NHPI has been documented in diverse taxa
 Insects, fishes, amphibians, birds, and mammals
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Habitat selection and conservation biology:
translocation and captive-release programs
 Conservation efforts using translocation (moving
animals from one part of their natural range to another)
and captive-release programs (breeding animals in
captivity and then releasing them to the wild) often fail


Animals travel long distances away from the release site
Survivors may exhibit decreased condition and
reproduction
 Movement away from the release site make provisioning
and monitoring extremely difficult
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 Many translocated animals travel long distances
from the site of release. In cougars (美洲獅) , this
is especially true for adult males.
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Making captive-release programs and
translocations work
 Movement from a release site suggests that the animal
rejects the habitat and is searching for suitable habitat
 Understanding habitat selection and natal habitat
preference induction may inspire modifications to
programs



And help animals find the release site more acceptable
Providing captive animals with stimuli and cues similar to
those at the release site
May make them more inclined to stay at the release site
 Placing stimuli and cues from the original habitat at the
release site might reduce the disparity between the two
habitats
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Habitat selection and conservation biology:
ecological traps
 Ecological trap (生態陷阱): a low quality habitat that
animals prefer over a high quality habitat
 Cooper’s hawks in Arizona select Tucson because of its
plentiful nest sites and prey (pigeons and doves)




Urban hawks nest earlier and have larger clutches
But nestling mortality is higher in Tucson than rural areas
Prey carry trichomoniasis (滴蟲病) , which kills nestling
hawks
The hawks selected an inferior habitat – an ecological trap
 Populations in an ecological trap move toward extinction
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Cooper's Hawk
 Cooper's Hawk (Accipiter
cooperii) is a medium-sized hawk
native to the North American
continent and found from Canada
to Mexico.
 As in many birds of prey, the
male is smaller than the female.
The birds found east of the
Mississippi River tend to be
larger on average than the birds
found to the west.
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Migration
 Migration: movement away from the home range that
does not stop upon encountering the first suitable
location


Animals move until they respond to the presence of
resources (nest sites and food), and then they stop
Migratory movements occur over greater distances than
dispersal
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 Migrating caribou marching through Alaska in
July. During the spring, many caribou breed in
the tundra. Beginning in July, they migrate south,
where food will be available through winter.
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Migration: one-way or round trip
 In some species, migration involves movement away
from an area and the subsequent return to that area


Migration between breeding areas and over wintering,
or feeding, areas
Associated with long-lived species (e.g., vertebrates)
 In other species, migration is a one-way affair
 Migratory insects permanently abandon their site of
origin
 Associated with short-lived species (e.g., insects)
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Animals vary in the distance they
migrate
 A salamander travels less than a kilometer from its
woodland home to its breeding pond
 Northern elephant seals migrate twice a year from beaches
in southern California to northern feeding grounds in the
Aleutian Islands - 8000 kilometers each year
 The arctic tern migrates 20,000 kilometers one-way,
between its southern wintering area and northern breeding
area
 Long distance migrants insects: desert locusts and monarch
butterflies have one-way migration distances of 5,000 km
and 3,600 km, respectively
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 arctic tern
 elephant seals
 desert locusts
 monarch
Ayo 教材 (動物行為學 2010)
 salamander
65
Migration can take several forms
 Migration can be obligate: an individual always migrates
 Facultative migrants migrate only if local conditions
deteriorate
 Differential migration: migration of individuals differs
by age or gender


Small passerines (perching birds) may migrate in their first
year but remain on breeding grounds in subsequent years
Female and juvenile blue tits migrate because they are less
able to compete for food on the breeding grounds when it
becomes scarce during the nonbreeding period
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Costs of migration
 Animals migrate because they produce more offspring
this way then if they stayed put
 But, migration takes a tremendous toll

Less than half of the waterfowl in North America that
migrate south each fall return to their breeding grounds
 The mortality rate of black-throated blue warblers is
15 times higher during spring and autumn migration
than during periods when individuals are not migrating
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Costs of migration: energy
 Traveling long distances requires a great deal of energy
 Bird use 6-8 times more energy when flying than resting
 Natural selection favors behaviors that reduce the risk of
starvation during migration
 Storing fat before the journey begins



Fat provides more energy than carbohydrates or proteins
Insects, fish, birds, and mammals put on fat reserves
The body mass of long-distance migratory birds can double
 Increasing body mass to avoid starvation must be
balanced against the negative effects of a heavy fuel load
while flying
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Saving energy during migration: stopovers
 Some animals do not have sufficient fat stores to
migrate without stopping
 Small birds reduce their risk of starvation by refueling
along the way


They alternate flight and stopovers
Spending more time in stopover than in flight
 How do they know where to stop for food?
 They use landscape features (i.e. amount of hardwood
forests) which are positively correlated with arthropod
abundance
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Fly-and-forage migration
 Ospreys combine foraging and migration
 Individuals forage for fish in nearby bodies of water
 They move on in less than 12 hours
 Other birds (i.e. falcons and seabirds) that fly extensively
also use this strategy

Birds that feed on the ground or in vegetation have longer
stopovers
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 ← 鶚（學名：Pandion
haliaetus）或稱作魚鷹，
是一種善於捕魚的猛禽。
 鶚在隼形目中屬於鶚科，
這個科只有一屬一種。
 隼屬（學名Falco）在生物分類
學上是隼形目隼科中的一個屬，
屬於小型猛禽，現存共有三十
多種。→
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Costs of migration: risk of predation
 Migrants experience heavy predation
 Predation risk has shaped timing and routing of migration
 The predator landscape for migrants has two components
 Non-migratory predators along the route and the endpoints
 Migratory predators
 Lions, cheetahs (獵豹) , and hyenas (鬣狗) track
African ungulates(有蹄類)



Wolves follow North American caribou
Water pythons(蟒蛇) migrate seasonally to follow dusky
rats
Songbirds flying south face five million raptors (猛禽類)
that are also making the trip
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Costs of migration: inclement weather
(險惡的天氣)
 Migration occurs during the spring and fall
 Unstable weather drastically raises the cost of migration
 Severe rainstorms and snowstorms kill millions of migrating
monarch butterflies
 In birds, the most devastating mortality occurs when land
species encounter storms over water


A sudden snowstorm in Minnesota killed 1.5 million
Lapland longspurs (鐵爪鵐)
Unseasonably cold temperatures after arriving at breeding
areas or before departing from such areas kills migrants
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Costs of migration: obstacles
 Birds crash into lighthouses, skyscrapers, and TV
towers

In a single night, seven towers in Illinois felled 3,200
birds
 Wind-powered turbines that generate electricity have
been erected in many locations

Both on a small scale and large-scale wind farms
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Wind turbines kill migrants
 Particularly for nocturnally active birds and bats
 Direct problems: animals collide with wind turbines
 Indirect problems result from changes to the landscape
(e.g., construction of roads, buildings, and electrical
transmission lines)
 Monitoring fatalities at wind facilities is hard
 Issues of searcher efficiency
 Removal of carcasses by scavengers before they can be
counted
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Benefits of migration: energy profit
 Animals trade a less hospitable
habitat for a more hospitable one

Each fall, millions of monarch
butterflies migrate southward
from Canada and the United
States to fir forests in central
Mexico
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Monarch butterflies settle in forests
 The forest is cool but not freezing
 Freezing temperatures kill
monarchs
 Warmer temperatures elevate
metabolic rates and waste energy
reserves
 Tall trees provide branches on
which the butterflies can roost

Their thick, protective canopy
shields them from rain, snow, or
hail
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Forests protect migrating monarchs
 A dry monarch withstands colder temperatures better
than one with water on its body
 The forest canopy also serves as a blanket that keeps
the butterflies warm
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Climate changes affect food supply
 Migration permits exploitation of temporary or moving
resources
 Larvae of monarch butterflies feed only on milkweed
(乳草)

In the eastern United States, the plants grow during
spring and summer
 Despite the energy required for migration, energy is
saved

By avoiding temperature stresses of northern winters,
species compensate for the energy spent on migration
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Benefits of migration: reproductive benefits
 If there is so much food in the
warmer winter habitats, why do
species migrate?
 There are advantages in rearing
broods in the summer habitats



Long days in the far north
Birds can bring more food to
their offspring
Species that breed farther north
have larger broods
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Areas provide conditions for breeding
 Species migrate to areas that provide the necessary
conditions for breeding or that offer protection from
predators
 Gray and humpback whales breed in warm coastal
bays and lagoons which help protect the calves from
predation
 Seals(海狗), sea lions(海獅), and walrus(海象)
migrate to protected rookery sites
 Sea turtles migrate thousands of kilometers between
feeding grounds and breeding areas

Isolated beaches have fewer predators
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座頭鯨
 座頭鯨（學名：Megaptera novaeangliae），又名
大翅鯨、駝背鯨、巨臂鯨，屬於鬚鯨亞目的海洋
哺乳動物。該物種為大型鯨魚：成年鯨身長可達
12至16米之間（40至50英尺），目前最大記錄的
雌性可達18米。體重25至35噸（36噸合79,000
磅）。座頭鯨以其躍出水面姿勢、超長的前翅與
複雜的叫聲而聞名。全世界各大海洋都有座頭鯨
的蹤跡，是賞鯨者的最愛之一。已列入《瀕危野
生動植物種國際貿易公約》目錄。
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灰鯨
 灰鯨（Eschrichtius robustus），現又稱東太平洋灰




鯨，是一種每年來往攝食區和繁殖區的鯨。
在中國，分布於黃海、東海等海域，多棲息於熱
帶及暖溫帶海域。
該物種的模式產地在瑞典。牠們約有16 米長，36
公頓重，一般可活到50–60歲。
灰鯨曾一度被稱為「魔鬼魚」，因為當牠們被追
獵時會奮力搏鬥。
灰鯨是灰鯨屬中唯一的物種，亦是灰鯨科中唯一
的物種。這種動物是最古老的物種之一，在地球
上已有約3000萬年的歷史。在很久之前牠們一度
是巨牙鯊的捕食對象（巨牙鯊現已滅絕）。
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海龜
 Some green turtles migrate
from their feeding ground
off the coast of Brazil to
Ascension island to breed
on sheltered beaches, where
it is safe from predators.
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Benefits of migration: reduced competition
and predation
 Animals returning to the temperate zone escape the
intense competition found in warmer, more densely
populated areas

Without competition from nonmigrants in the tropics
 Returning to temperate zones to breed reduces predation
 In the far north, breeding periods are very short
 Birds nest simultaneously, reducing the likelihood of any
single individual being taken by a predator
 With decreased food, predator numbers are kept low
 Migratory species deprive parasites and microorganisms
of permanent hosts
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Migration and conservation biology
 Long distance migrations, one of the most spectacular of
biological phenomena, are becoming increasingly rare events
 The Greater Yellowstone Ecosystem is a 19 million acre
temperate ecosystem in Idaho, Wyoming, and Montana


All 14 bison(北美野牛) migration routes have been lost
And 78% of the pronghorn(叉角羚) and 58% of elk (駝鹿)
routes are gone
 Causes include: increased human population and habitat loss
 Fences, highways, and housing subdivisions block routes
 One solution: create a protected network of wildlife
migration corridors (遷徙廊道)
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Summary
 Natal dispersal: permanent movement away from the natal





area or social group
In natal philopatry, offspring remain at their birth place
Breeding dispersal: movement between two breeding areas or
social groups
Costs of philopatry: inbreeding, reproductive suppression, and
competition with relatives for mates or resources
Advantages of philopatry: genes are suited to local conditions,
familiarity with the local physical and social setting
Dispersers face high energy costs and risks of predation,
increased movement and lack of familiarity with the
environment
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Summary
 Patterns of dispersal are due to: inbreeding avoidance,





resource competition, mate competition, and cooperative
behavior
Habitat selection involves search, settlement, and residency
Habitat selection uses comparison (best of N) strategies and
sequential search strategies
Migration occurs over greater distances than dispersal
Costs of migration: energy expenditure, risks of predation,
unfamiliar and inhospitable terrain, and severe weather
Advantages of migration: favorable energy balance, escaping
harsh temperatures, avoiding competition from reduced food,
and reduced predation and parasitism
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問題與討論
[email protected]
 Ayo 台南 NUTN 站
http://myweb.nutn.edu.tw/~hycheng/
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