Benefits of Grouping

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Benefits of Groups
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• Predation
• Foraging
• Finding a Mate
• Thermoregulation and Water Conservation

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Predation
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Reduced Risk of Predation

• Anti-predator Vigilance
• Dilution of risk
• Predator confusion

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Anti-predator Vigilance

• Classic Many Eyes theory
• suggests that more eyes are able to detect a
  predator earlier
• as group size increases, individuals can decrease
  their own vigilance without increasing the risk
  of failing to detect an attack.

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Sparrows and Finches, Pulliam, 1988
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Dilution of Risk

• As group size increases, individuals can reduce
  their risk of being killed by grouping, even when
  the risk that someone in the group will be
  captured stays constant.

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Selfish Herds

• Hamiltons Selfish Herd Theory
• If a predator captures the first prey item that
  it comes across, then an individual animal is
  more vulnerable to predation than an animal
  within a group.

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Confusion of Predators

• There is an exponential decrease in predator
  success with increasing group size.
• four different aquatic predators all were less
  successful at attacking prey fish in groups
  rather than individual fish
• Neill Cullen, 1974

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• Foraging

Foraging
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1.Locating Food

• Less time spent looking for food
• Benkman (1988) showed search time to best tree
  (49 seeds) reduced by 50 when foraging with a
  partner.
• Fish play follow the leader. Reebs (2000)
  demonstrated that one knowledgeable fish could
  guide the rest of the shoal to food.

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2.Catch difficult prey

• Easier to catch large prey
• Creel and Creel (1995)
• African wild dogs 2025 kg whose major prey are
  ungulates ranging from 15 to 200 kg
• This study showed that hunting success, prey mass
  and the probability of multiple kills increased
  with number of adults

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3.Colonies/Roosts as Information Centres (or
mutual parasitism?)

• Unsuccessful members of a colony can follow
  successful members to a food source.
• Benefit to successful member? Another day he may
  need to follow a group member to food.

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• Wilkinson .G. (1991) showed that the evening bat
  (Nycticeius humeralis) transfers information
  about the location and abundance of food patches
  to the rest of the group.
• Vampire Bats live in colonies, an unsuccessful
  member can persuade a successful neighbour to
  donate blood. The benefit will be returned to the
  donating bat another night when he has been
  unsuccessful.

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4. Vigilance

• ? chance that a predator will be spotted with
  increasing group size
• Ex. Ostrichs - the larger the group size, the
  more time spent foraging
• Ex. Clutton-Brock et al (1999)
• Meerkats - Sentinels allow increased foraging
  time for others

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5.Harvesting Renewing Food

• Group foraging most efficient manner with which
  to exploit habitats with renewing patches as
  individuals in groups are less likely to revisit
  patches that have already been exploited recently
  by others.
• Brent Geese and sea plantain. Geese leave 4 day
  gap intervals before revisiting patch.

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Finding a Mate
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Finding A Mate

• Sexual behaviour is a current hot topic in
  behavioural ecology
• The benefits associated with breeding in groups
  have received a great deal of sampling over the
  past number of years
• Benefits include increased matings, increased
  reproductive success, alloparenting, inclusive
  fitness

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• Being in a group where you may not be the most
  handsome or biggest male may not be so bad!
• Cooperation of males to get rid of dominant male
• Inclusive fitness in courtship displays

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• Alloparenting in Red ruffed lemurs (Varecia
  Ruvra) of the Masoala Peninsula, Madagascar
• Natalie Vasey

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• Mating occurs both within and between core
  groups- polygamous system
• Two months after birth, core group members range
  more widely, and the network of care providers
  grows larger
• Among the types of allocare provided are
  allonursing, co-stashing, infant guarding, and
  adoption

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• Alloparenting behavior appears be an integral
  part of the ruffed lemur's reproductive strategy
• Improving survivorship of young by protection
• Also the fitness of parents- more time to forage
  and socially engage with others

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• Have winter spacing patterns of Harlequin Ducks
  been partially shaped by sexual selection?
• Rodway, Michael S

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• Typically dispersed in small groups
• Sexually-selected changes in spacing to
  facilitate courtship and mate sampling
• Behaviour similar to lekking was observed

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Thermoregulation and Water Conservation

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Thermoregulation

• is the maintenance of an internal body
  temperature within a range.
• Need to conserve heat.
• Solitary animals may find it difficult to cover
  the cost of this.
• Social animals share the cost of keeping warm
  between them

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Conserving heat.

• There are a number of ways which animals may
  conserve heat
• Huddling
• Warming the air around them, which works for
  those who live in confined spaces such as
  burrows.
• - initial cost involved
• - saving energy in the long run.

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Huddling

• two or more individuals in close contact with
  each other.
• Reduces surface area - to - volume ratio, and so
  there is less exposed surface area over which
  heat can be lost.
• Assumes that both of the sides in contact are the
  same temperature, therefore there is no heat
  loss.
• This benefit increases with group size.
• It is seen in a number of bird, insect and
  mammalian species.

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Kotze et al. (2008) experiment

• Damaraland Mole Rat Vs Natal Mole Rat.
• Compare energetics of huddling in both.
• Measured oxygen consumption (VO2) in groups
  ranging from 1 to 15 in size at different ambient
  temperatures (14, 18, 22, 26, 30oC)
• Results
• VO2 increased with increasing group size.
• D. VO2 gt N. VO2

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Emperor Penguins

• Two experiments
• Gilbert (1996) Male penguins spend only 38 18
  of incubation period huddling with other
  incubating males.
• Temperature during this period is over 20oC for
  about 13 12 of huddling time.
• - Allows all males to get equal and regular
  access to a warm environment, allowing them to
  save energy to successfully incubate their eggs.

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Emperor Penguins

• G.H. Visser(2007)
• Compares males who huddle, and those that dont
  while incubating eggs.
• Group 1 Incubating and Huddle.
• Group 2 Just Incubating.
• Results
• Incubating alone resulted in an elevation rate
  of 20, store of fats diminished fairly fast and
  a higher incidence of egg desertion.

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More Examples

• Birds roosting Best way to conserve energy?
• Beauchamp (1999) any energy saved in roosting
  is spent on the transport to get to the roosting
  sites.
• Honeybees increase their heat production and
  huddle together to retain heat.
• Deer mice initial socialisation is expensive but
  thermal conductance and mass specific metabolic
  rate by 30 within 5 days (Andrews, 1986).

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Water Conservation

• Better for those on periphery of group.
• Many animals cluster so as to conserve water, e.g
  slugs pack close so that large areas of their
  flanks are in contact gt minimising area over
  which evaporation can occur.
• Many animals will lay their eggs in clusters so
  they are protected from desiccation.

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Desiccation Hypothesis

• Stamp (1980) egg clustering is adaptive per se
  by reducing egg mortality due to desiccation.
• Clark and Faeth (1997) Natural variation and
  Experimental variation in cluster size and the
  success of the hatches at varying levels of
  controlled humidity.
• Found that hatch successes were positively
  related to relative humidity.
• Layers also helped in water conservation.
• Support for Hypothesis North American
  Lepidopteran species cluster their eggs tightly,
  those in tropical areas lay eggs singly or in
  loose monolayers.

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References

• Andrews, R. V., Belknap, R. W., (1986),
  Bioenergetic benefits of huddling by deer mice
  (Peromyscus maniculatus), Comparative
  Biochemistry and Physiology. A, Comparative
  Physiology, 85(4), 775-778
• Benkman, C. W., 1988, Flock size, food dispersion
  and the feeding behaviour of Crossbills.
  Behavioural Ecology and Sociobiology, 23, 167-75
• Benkman, C.W., and Pulliam, H.R. (1988). The
  Comparative Feeding Rates of North American
  Sparrows and Finches. Ecology, 69, 1195-1199.
• Clark, B. R., Faeth, S. H., (1998), The evolution
  of egg clustering in butterflies A test of the
  egg desiccation hypothesis, Evolutionary Ecology,
  12, 5, 543-552
• Clutton-Brock, T. H., O'Riain, M. J., Brotherton,
  P. N. M., Gaynor, D., Kansky, R., Griffin, A. S.
  and Manser, M. (1999), Selfish Sentinels in
  Cooperative Mammals. Science, 2845420, 1640-44
• Creel, S. and Creel, N.,M. (1995), Communal
  hunting and pack size in African wild dogs,
  Lycaon pictus, Animal Behaviour, 50, 1325-39

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• Gilbert, C., (2006), Huddling behaviour in
  Emperor penguins dynamics of huddling.
  Physiology and Behaviour, 88, 4-5, 479-488
• Hamilton,W.D. (1971). Geometry for Selfish Herd.
  Journal of Theoretical Biology, 31, 295.
• Kotze, J., Bennett, N. C., Scantlebury, M.,
  (2008), The energetics of huddling in two species
  of Mole-rat (RodentiaBathyergidae), Physiology
  and Behaviour, 93, 1-2, 215-221
• Lima,S.L. (1993). Back to the basics of
  anti-predatory vigilance the group-size effect
  Animal Behaviour , 58 , 3 , 537 - 543
• Neill, S. R. St. J. and Cullen, J. M. (1974).
  Experiments on whether schooling of prey affects
  hunting behaviour of cephalopods and fish
  predators. Journal of Zoology, 170, 549-69
• Reebs, S.G, (2000), Can a minority of informed
  leaders determine the foraging movements of a
  fish shoal?, Animal Behaviour, 59, 403-409

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• Wilkinson, G., (1992), Information transfer at
  evening bat colonies, Animal Behaviour, 44,
  501-518
• Visser, G. H., (2007), Regulation of energy
  expenditure in free-living animals under extreme
  conditions, Appetite, 49, 1, 338