Transcript Cooperative Breeding - Ecology and Evolutionary Biology

Groove-billed ani
Cooperative Breeding
JodyLee Estrada Duek, Ph.D.
With assistance from Dr. Gary Ritchison
http://people.eku.edu/ritchisong/matingsystems.html
Cooperative Breeding 1
• "Cooperative" or "communal" breeding occurs when more than two
birds of the same species provide care in rearing the young from one
nest.
• About 3 percent (approximately 300 species) of bird species
worldwide are cooperative breeders.
• There are two types of cooperative arrangements:
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those in which mature nonbreeders ("helpers-at-the-nest" or "auxiliaries")
help protect and rear the young, but are not parents of any of them,
those where there is some degree of shared parentage of offspring.
• Cooperative breeders may exhibit shared maternity, shared paternity,
or both.
Cooperative Breeding 2
• 'helpers' provide parental care for young that are not their own
• care given usually includes food, but other types of care are also
common, such as territorial defense, nest construction, incubation,
and defense from predators
• observed in over 220 species of birds
• occurs most frequently in the tropics & Australia; less common in
Europe & North America
Cooperative Breeding 3
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The best-studied North American cooperative breeders, Scrub-Jay, Gray-breasted (Mexican)
Jay, Groove-billed Ani, Acorn Woodpecker, differ in the details of their breeding biology.
Scrub jays in Florida represent a group of populations that probably were once in contact
with the widespread western populations but are now totally isolated.
Only in Florida are Scrub jays cooperative breeders, and there they reside in permanent,
group-defended territories
Ornithologists Woolfenden and Fitzpatrick found groups consist of a permanently bonded
monogamous pair and one to six helpers, generally the pair's offspring
Half the territories are occupied by pairs without helpers; most others have one or two
Although pairing and breeding can occur after one year as a helper, birds often spend
several years as nonbreeding auxiliaries
Males may remain up to six years; females usually disperse and pair after one or two years
Helpers participate in all nonsexual activities except nest construction, egg laying, and
incubation.
Pairs with helpers are more successful -- they fledge one and a half times more young than
pairs without helpers.
Cooperative breeders’ characteristics:
• low breeding rates
• high adult survival
• limited dispersal
• deferred maturity (may not breed
until at least 2 years old)
Gray-breasted
(Mexican) jay
Cooperative breeding in
suboscines
• In the 1097 species of New World suboscines, (in general,
any bird of the suborders Eurylaimi, Tyranni, and Menurae
of the order Passeriformes - perching birds, or passerines as distinguished from an oscine, or songbird. The term
suboscine implies more primitive in anatomy and
behaviour than the oscines) cooperative breeding is rare,
inferred in just 16 species.
Cooperative breeding in oscines
• By contrast, a larger proportion of oscines are cooperative
breeders (577 of 4456 species; 13%). It is unlikely that
there is a simple ecological or life history explanation for
this difference. Both clades have diversified into an
enormous range of niches and show overlapping variation
in life history. The low prevalence in suboscines is unlikely
to be a result of the environment they occupy.
• Several oscine taxa have primarily radiated in the
Neotropics and hence overlap the range of the New World
suboscines. Many of these have a high incidence of
cooperation (e.g., New World jays, mimids, emberizids,
icterids and wrens).
Environmental Variability Drives the Evolution of
Cooperative Breeding in Vertebrates, in Birds
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Many vertebrates breed in cooperative groups in which more than two members
provide care for young.
Studies of cooperative breeding behavior within species have long highlighted the
importance of environmental factors in mediating the paradox of why some such
individuals delay independent breeding to help raise the offspring of others.
In contrast, studies involving comparisons among species have not shown a similarly
clear evolutionary-scale relationship between the interspecific incidence of cooperative
breeding and any environmental factors.
Rubenstein and Lovette 2007 used a phylogenetically controlled comparative analysis of
a complete, socially diverse group of birds — 45 species of African starlings — to show
that cooperative breeding is positively associated with living in semiarid savanna
habitats and with temporal variability in rainfall.
Savanna habitats are not only highly seasonal, but also temporally variable and
unpredictable, and this temporal variability directly influences individual reproductive
decisions in starlings and helps explain interspecific patterns of sociality.
Cooperative breeding is adaptive in temporally variable environments because it allows
for some reproduction in harsh years and sustained breeding during benign years.
This “temporal variability” hypothesis might help explain the phylogenetic and
geographic concentrations of cooperatively breeding vertebrates in savanna-like
habitats and other temporally variable environments worldwide.
Superb starling
• A Superb Starling, a cooperative breeding savanna dweller abundant
throughout northeast Africa (Dustin R. Rubenstein photo).
Possible explanations
Costs or Benefits to
Helpers
Costs or Benefits to
Breeders
Explanation
decrease in fitness
increase in fitness
helpers are
altruistic
increase in fitness
decrease in fitness
helpers are selfish
increase in fitness
both helpers &
breeders benefit
increase in fitness
A 'test' of these
explanations: 1
Gray-crowned babbler
• Gray-crowned Babblers: Brown & Brown (1981) removed helpers
from some groups and studied breeding success of
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large groups (no helpers removed)
experimentally-reduced groups
natural small groups
• Possible outcomes:
– if helpers increase breeding success, removal would decrease breeding success
to a level comparable to natural small groups
– if helpers decrease breeding success, removal would increase breeding success
– if helpers are 'neutral', removal would not influence breeding success
A 'test' of these explanations: 2
• Results:
– Large groups averaged 2.4 young/group
– Reduced groups averaged 0.8 young/group
• Conclusion: Helpers do help but might be able to do better on their
own (& this also appears to be true in Scrub Jays ).
Scrub jay
Photo: Ray Wilson
Cactus wrens
Cactus wren, Tucson
• Live in family groups
with DR
• Siblings stay in family
territory but do not
assist at the nest
• Adults build a series of
nests during the year,
with sequential
clutches
• Each clutch takes over
one or more recent
nests as parents move
to a new nest, begin
again
Why do helpers 'stay at
home' & help?
• Young birds delay dispersal & reproduction :
– dispersal is risky
• unfamiliar habitats with unpredictable food supplies
• increased predation risk
Acorn woodpecker granary
– available habitat saturated (all territories occupied)
– only the 'home' territory may have essential resources. For example:
• acorn storage sites for Acorn Woodpeckers (photo)
• cavities for Red-cockaded Woodpeckers
– they may not have the skills needed to breed on their own, e.g., skills needed
to acquire & defend a territory or to care for young
– harsh conditions (such as drought) may make successful breeding unlikely for
birds on their own (that is, without helpers)
Acorn Woodpeckers 1
• Long-term studies of Acorn Woodpeckers have been conducted by a
succession of ornithologists, including M. H. and B. R. MacRoberts,
Koenig, Mumme, and Pitelka in central coastal California
• There Acorn Woodpecker groups are composed of up to 15 members
whose territories are based on the defense and maintenance of
granaries in which they store acorns
• Groups consist largely of siblings, their cousins, and their parents
• Some of the sexually mature birds are nonbreeding helpers
• Within each group, up to four males may mate with one (or
occasionally two) females, and all eggs are laid in a single nest
• Paternity and sometimes maternity of communal clutch is shared
Acorn Woodpeckers 2
• Per capita reproductive success generally increases with group size up
to 7 or 8 members, and then declines
• Clutches produced by two females are somewhat less successful than
those of single females due to behavioral interference between the
two females and some egg tossing
• Although there is some geographic variation in the size of groups and
other aspects of the Acorn Woodpecker system, it breeds
cooperatively throughout its range
Acorn Woodpecker
http://video.google.com/videoplay?docid=6656661551287167267&q=acorn+woodpecker&total=26&start=0&num=10&so=0&type=search&plindex=4
• Cooperative strategies include storage of
acorns for future use
Major hypotheses for DR
1. ecological constraint; Emlen (1982): hypothesis DR response to constraints on dispersal
options. Habitat saturation or environmental variation leads to lack of high-quality openings
so offspring delay dispersal
strong point: manipulation of constraints explains dispersal patterns within some species
weak point: most species face some constraints and do not delay dispersal; does not
explain interspecific variation
2. life-history; Arnold & Owens (1998): hypothesis DR has a phylogenetic component and is
more frequent in long-lived species -- they occupy territories longer, leading to habitat
saturation and preventing younger individuals from obtaining breeding positions
strong point: partly explains phylogenetic pattern of DR and attempts to reconcile
cooperation with life-history correlates
weak point: majority of long-lived species are not cooperative; in practice proposes same
mechanism as the EC hypothesis and hence has same weak points
3. prolonged investment: parental nepotism; Brown (1987); Ekman et al. (2001a): hypothesis:
offspring gain direct fitness benefits from prolonged association with parents due to
nepotistic parental behaviours that improve offspring fitness
strong point: explains why offspring should prefer to wait for the onset of reproduction at
home; provides basis to understand family formation. brings together parental investment
and life-history characteristics
weak point: neglects the role of life-history characteristics on reproductive decisions of
offspring; does not entirely explain interspecific variation
Proposed pathway leading to family
formation in birds 1
• Effects of life history and environmental factors on parental
decisions are illustrated by the grey arrows
• Effects on offspring decisions are shown by the black
arrows.
• The environmental factors are shown in boxes.
• The directions of the relationships between
traits or factors are illustrated by 'plus' for
positive correlations and 'minus' for negative
correlations. + Red-cockaded woodpecker
Proposed pathway leading to family
formation in birds 2: Conclusions
• Species with high survival tend to start breeding later in life and can
invest more in offspring
• These two factors combined can cause offspring to delay dispersal,
leading to the formation of families
• Environmental factors such as good breeding conditions promote
dispersal
• Resource availability allows parents to invest more in offspring
without incurring strong costs
• However, parents should only prolong investment in offspring if this
increases offspring survival prospects substantially without
compromising parents’ own survival
• Thus, there should not be parental investment when offspring
survival is too low or too high
Life history and the evolution of family living in birds // Rita Covas and Michael Griesser
Florida Scrub-Jays + Western Scrub-Jays
• Florida Scrub-Jays are largely restricted to the scattered and now
much reduced oak scrub habitat; reproductive success outside of oak
scrub is very poor.
• All available habitat is occupied, and populations appear to be stable
from year to year, which means young birds are unlikely to find
vacant space to set up territories of their own.
• In contrast, Western Scrub-Jays generally
are not space-limited, and the probability
of a young bird leaving home and finding
a territory in which to breed is high.
Gray-breasted Jay
• Like the Florida Scrub-Jay, the closely related Gray-breasted Jay of
the southwestern U.S. lives in permanent group-defended
territories, and breeding adults are monogamous
• Studies by ethologist Jerram Brown and colleagues have shown
the cooperative system of this species is more complex than that
of its southeastern relatives in several ways
• Gray-breasted Jay groups are much larger, ranging from 8 to 18
individuals; thus, they usually include offspring from more than
just the preceding year.
• Within each group, two and sometimes three breeding pairs nest
separately but simultaneously each season, and some
interference among them often occurs
• Interference involves the theft of nest-lining materials, but can
include the tossing of eggs from nests by females of rival nests
• Although the laying female does all the incubating, she is fed by
her mate and by auxiliaries.
• Nestlings receive more than half of their feedings from auxiliaries.
Life history and the evolution of family living in birds 1
(article)
• why do some bird species live in family groups? important unanswered question
• Families arise when young delay onset of independent reproduction and remain
with parents beyond independence
• Explanations have focused on dispersal constraints, such as absence of high-quality
breeding openings
• However, although constraints successfully explain within-population dispersal
decisions, they fail as an ultimate explanation for variation in family formation
across species.
• Most family-living species are long-lived and recent life-history studies
demonstrate that delayed reproduction can be adaptive in long-lived species
• Delayed dispersal and reproduction might be an adaptive life-history decision
• Covas & Griesser (2007) suggest longevity favors delayed onset of reproduction and
gives parents opportunity of prolonged investment in offspring, an option that is
not available for short-lived species.
• Yet, parents should only prolong their investment in offspring if this increases
offspring survival and outweighs the fitness cost that parents incur, which is only
possible under ecological conditions such as predictable access to resources.
• Covas & Griesser (2007) therefore propose that both life-history and ecological
factors play a role in determining the evolution of family living across species.
Life history and the evolution of family living in birds 2
• The proposed framework does not exclude the possibility that family
associations might arise through different pathways
• Long-tailed Tits (Aegithalos caudatus) are short-lived and individuals always
attempt to breed in their first year of life, as predicted by life-history theory
• In this species, family cohesion is reached through a different pathway
• Owing to high nest predation, population density is low, reducing kin
competition and giving offspring the option to delay dispersal and remain
associated with their parents throughout their first winter
• Then, they disperse and attempt to reproduce independently, but return to
the parental territory to help their relatives if breeding attempt fails
• In this species, family living seems unrelated to life-history characteristics
and appears linked to environmental factors that allow family structure to
be kept after breeding season and to nesting in close spatial association
• http://www.youtube.com/watch?v=jB0Ia65vngo long-tailed tits
Groove-billed Ani 1
• Although the Groove-billed Ani breeds in
southern Texas, our knowledge of its breeding
biology comes from the work of sociobiologist
Sandra Vehrencamp who worked in Costa Rica.
• The groups defending permanent territories consist of one to four
monogamous breeding pairs that may include an unpaired helper.
• All members of the group participate in building a single nest into
which all females lay their eggs
• Incubation and care of the young are shared by all
• Beyond a certain clutch size, some eggs tend to be buried and fail to
receive proper incubation, leading to decreased probability of any
given egg hatching.
Groove-billed Ani 2
• Unlike the "cooperative" breeders that they appear to be, female anis
engage in behaviors that increase the probability of their own eggs
being the successful ones in the communal clutch
• The most effective of these behaviors is the tossing of other females'
eggs from the nest
• In spite of the increased competition and conflict, multipair groups
manage to fledge more young per individual than do single pairs in
similar habitats
Why Cooperative Breeding?
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Why has evolution produced cooperative breeding systems? Initial hypotheses were based
on kin selection (seemingly "selfless" behavior like helping at the nest being favored because
it increases the reproductive success of relatives genetically similar to the helper) or on
maximizing of reproductive output. As more cooperatively breeding species have been
examined worldwide, these explanations generally have not been supported. Instead,
cooperative systems appear to arise when environmental constraints force birds into
breeding groups because the opportunities for younger birds to breed independently are
severely limited. Limitations may include a shortage of territory openings because higher
quality habitats are saturated with established breeders; a shortage of sexual partners
(generally females), indicated by the skewed sex ratios that are common in groups; and
unpredictable availability of resources, which could make it too risky for individual pairs to
commit themselves to reproduce in any given year. That cooperative breeding is a common
strategy in arid and semiarid portions of Africa and Australia lends strong support to this line
of reasoning. Cooperative breeding may be viewed primarily as a means by which young
adults put off the start of their own breeding in order to maximize their lifetime
reproductive output, and in the process occasionally promote genes identical with their own
via kin selection.
Not always complete cooperation
• Acorn woodpecker females replacement story
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http://video.google.com/videoplay?docid=6130761313069739265
• Gray-crowned babbler
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http://video.google.com/videoplay?docid=5020960287597912571&q=bird+%2B+babblers&total=23&start=0&num=10
&so=0&type=search&plindex=4