Intraspecific Competition

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Intraspecific Competition

• 5th edition -- pp 411-426, Chp. 19
• 6th edition -- pp 194-213, Chp. 12

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I. Density Stress

• As organisms become more crowded and food, space,
  mates must be shared.
• Under increasing density, social stress increases
  in vertebrates.

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How does stress act?
Stress is a physiological feedback involving
the endocrine system (pituitary adrenal glands).
STRESS
Hyperactivity of hypothalamus-pituitary-adrenocort
iscular system.
Change in secretion of growth sex hormones
(gonadotrophic)
Change in hormones

• Suppressed Growth
• curtailed reproductive functions
• delayed sexual maturity
• may also suppress immune system increased
  disease mortality.

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Pheremones (Anyone know what these are?)
Chemicals released by animals that serve as
communication among individuals of the same
species. These chemicals are present in the
urine of adult rodents and these pheremones have
been shown to inhibit reproduction.

• In Wild House Mice
• Found urine from high density females resulted in
  delayed maturity.
• Urine from low density females had no effect.
• Also, juvenile low-density mice exposed to urine
  of dominant males led to early puberty.

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II. Dispersal
The who, what, when, where and how of
dispersal. General Belief animals disperse
beause they are driven off by competition Who
Disperses? Howard (1960) defines dispersal as
the permanent movement of individuals from a
birth site to a place where it reproduces, or
would have reproduced had it survived and found a
mate. THIS suggests it is the young who migrate!
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Among Birds Young are the major
dispersers. Greenwood (1980) suggests natal
dispersal - young dispersing. Breeding
dispersal - movement of adults from poor to
better reproductive sites.
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Among Rodents Most dispersers are sub-adult
males and females (dispersers tend to be smaller
lighter than stay-at-homes). Among Insects
many groups have dispersal through polymorphic
winged versions among normally flightless
insects.
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Sometimes Dispersal causes problems...

• Sea lions in California, dispersing males eating
  endangered salmon in river mouths/harbors.
• Male black bears dispersing getting into
  trouble in PA.

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When how far to disperse?
WHEN? Most disperse in pre-reproductive periods
(e.g. squirrels and many other NA mammals in
fall- spring breeders). How Far? Most are
seeking vacant habitats, so the distance traveled
will depend upon density of surrounding
populations and the availability of suitable,
un-occupied areas.
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Examples of Dispersal
1. Colony-nesting Monk Parakeets 91 of
banded young remained with their parents until 3
months old. young birds left graduall
intermittantly in random directions until early
next breeding season (natal dispersal).
distance dispersed was 300 - 2000 m (mean 1230
m). breeding dispersals were only 500 m. THM-
in this case, most dispersal was NATAL, natal
dispersals were much greater distance than
BREEDING dispersals.
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Examples of Dispersal
2. Red Squirrels at Fort Assiniboine, Alberta
Prior to settlement, age-0 made exploratory
forrays of up to 900 m from natal territory.
About 50 settled either on, or adjacent to the
mothers territory. farthest distance
dispersed was 323 m OR about 3 territory
widths.
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Why Disperse?Why should ayoung animal disperse
and leave its natal area for a strange
place? Some Dont!Whatever the choice,
there are certain costs benefits.1. Those
that stay.unless they are dominant and replace
dead adults there is little chance of
reproducing.2. Most juveniles or sub-adults
can maximize their fitness only by leaving
their birthplace depsite the risks.
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Benefits of dispersal

• May locate a new habitat where resources are
  more available, more breeding sites, less
  competition.
• Incresed likelihood of finding new individuals
  with which to mate (this reduces inbreeding may
  increase fitness of offspring due to higher
  heterozygosity).
• In Rodents high density leads to more
  aggressive behavior which leads to higher
  dispersal rates.

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Potential Costs Benefits of dispersal choices
(G genetic S somatic).______________________
_______________Stay At Home PhilopatryCosts
Benefits________________________________________
___Inbreeding depression (G) Optimal breeding
maintain locally adapted genes
(G)Reduced fitness due to Reduced
physical risksresource shortages (S)
increased survivorship (S)Reduced indirect
fitness Familarity with local Competition with
kin (S) terrain (S), familarity
w/ social environment (S),
adaption to local traditions (S),
maintain kin associations (S)
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Potential Costs Benefits of dispersal choices
(G genetic S somatic).______________________
_______________DisperseCosts Benefits_______
____________________________________Outbreeding
depression (G) Outbreedingdisrupt coadapted
genes. enhancement (G)Hybrid younf not
well-adapted Avoid overcrowding (S)(G)
Alleles less suited to Avoid
competition w/ kin (S) environment
(G) Greater risks in movement Improve
fecundity (S)predators, local diseases
unfamiliarity w/ terrain (S)
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Lidicker (1975) Hypothesizes 2 types of
Dispersal

• 1. Pre-saturation dispersal - occurs during the
  increasing phase of a population growth, before
  population peaks or resources are depleted.
• Individuals in good condition
• any sex group
• good chance of survival
• Seem density-independent.
• 2. Saturation dispersal - occurs when carrying
  capacity has been exceeded.
• Here, dispersal is mostly juveniles
  subdominants, that have two choices 1. Stay
  perish or not breed, OR
• 2. Leave area.(e.g OH squirrel hoards)
• If they leave, most will perish, but some may
  catch on elsewhere.

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Does Dispersal Regulate Populations?
NO !

• Dispersal can expand populations
• Aid in persistence of local populations
• AND function as a form of natural selection by
  sorting out phenotypes genotypes.

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SOCIAL INTERACTIONS
Aggressive and Submissive interactions
(agonistic) are the basis of social
organization. Two Forms of Social
Interaction 1. Dominance - social order based
on individual distance dominance relationships
(e.g. dogs). 2. Territoriality - division
exclusion of space by a social unit ot individual
with a social boundary. (e.g. crayfish, bass,
r.w. blackbird nesting territories).
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Simplest Form of Social Domiance
(Schjelderup - Ebbe 1922) with Domestic
Chickens.. ALPHA Straight-line peckin
g order BETA . OMEGA Submissi
ve to all others.
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Simplest Form of Social Domiance
A B Triangular peck order C

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More Complex Triangular
A B D C A is dominant over B, D
is the omega.
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0
12
11
6
2
5
4
3
2
12
0
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Dominance in Wolves
Wolves live in groups of 6-12 individuals called
packs. A pack is extended kin consisting of a
mated pair, 1 or more juveniles from the previous
year (sexually mature at 2), and several
non-breeding adults. Wolves have two social
heirarchies..
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Dominance in Wolves
Wolves have two social heirarchies.. One is
headed by the alpha male, one by the alpha
female. ? only the alpha female breeds-
mostly ? with alpha male, occasionally beta
male. ? all others rear feed pups. all
others.
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Dominance in Wolves

• Alphas always get enough food.
• When resources are limited the others suffer.
• Thus, births are _at_ every year within a pack.
• Each pack holds an exclusive area.
• When N increases, the percentage of females that
  reproduce goes down .leading to population
  regulation.

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Territoriality(Territory vs. Home Range)

• A Territory is a defended area, more or less
  fixed and exclusive, maintained by an individual
  or social group, (e.g. a wolf pack).
• A Home range is an area in which an animal
  normally lives, not necessarily defended by
  aggressive behavior.
• (A home range may overlap with another
  individuals)

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Types of Territories
Vary according to the needs of the
animals. 1. General purpose territory -
established during breeding season. Common to
muskrats, songbirds, mammals. It included
feeding, mating, and young rearing areas. 2.
Mating and Nesting territory - mating and nesting
territories with feeding done elsewhere (e.g.
prairie grouse, woodcock, swallows, seals, sea
lions, penguins). 3. Feeding territories - some
animals only defend feeding areas. (e.g.
hummingbirds, squirrels).
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Territorial Defense
Once a territory has been established, it must be
defended. Steps in defense 1. Songs or
Calls 2. Visual display 3. Attack chase
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Steps in defense 1. Songs or Calls - used by
birds frogs. If not heeded, physical actions
are required. - Songs of birds maintain spaces
in nesting areas. - if male is removed,
replaced immed. By another. - if song is
recorded played, other males stay out. 2.
Visual display - if calls not heeded gt visual
displays. crest raising fluffing of
feathers waiving wings erecting ears
baring fangs standing on hind legs (bears)
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Steps in defense If intimidation display
failsmore strenuous defense! 3. Attack
chase - just as it sounds. For example R.W.
Blackbirds bluegill sunfish in nest defense
from cuckholders.
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Other Forms of Territoriality...
Scent Marking - some animals defend and mark
territory with a well-placed scent post. Scent
posts warn intruders that they are tresspassing
and straying outside of their territory.
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Why Defend a Territory?
For acquisition preotection of a needed
resource such as food, reduced risk of predation,
or to attract a mate. Basic reason. An
increased probability of survival and improved
reproductive success, ie. Increased fitness.
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Territory Size

• As territory size increases, costs of defense go
  up.
• For that reason, territories tend to be only as
  big as can be defended.
• Territory size can change from year to year
  depending upon the availability of resources and
  the density of animals.

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Floaters
Contest competition among males for space leads
to some individuals being denied
territory. Thus, some portion of the population
is excluded from breeding due to exclusion from
suitable breeding sites. Excluded individuals
are a reserve of potentially breeding adults
ready to replace others or breed if a territory
becomes available. Some floaters co-exist in the
breeding territories of others, or they may set
up their own ranges outside of the area.
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Territories and Population Regulation
If no limit to territorial size exists and all
pairs can settle on an area and get a territory,
then territoriality only spaces out a
population. If territories have limited size,
then those that dont get a territory must
leave. In Arctic Ground Squirrels - all
females are allowed to nest. - polygamous males
drive excess males to submarginal habitat where
they exist as a non-breeding floating
population.