BIOL 203 Lecture 12: AquaticandTerrestrialEnvironments-Chapters11&14

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6 Feb 2017

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Animal Adaptations to Aquatic and Terrestrial Environments- Chapters 11 & 14
11.9- Social Behavior May Function to Limit Populations
Intraspecific competition can express itself in social behavior
Social behavior- the degree to which individuals of the same species tolerate one
Social behavior appears to be a mechanism that
Limits the number of animals living in a particular habitat
Limits the number of animals having access to a common food supply
Limits the number of animals engaging in reproductive activities
Social organization and group structure can be crucial to acquiring resources and
maintaining defense
Organization is often based on aggressiveness, intolerance, and the dominance of
one individual by another
Two opposing forces
Mutual attraction of individuals
Negative reaction against crowding-- the need for individual space
Each individual occupies a position in the group based on dominance and submissiveness
Alpha- individual dominant over all others
Beta- individual dominant over others except the alpha
Omega- the individual subordinate to all others
Social rank is determined by fighting, bluffing, and threatening at initial encounters or
through a series of encounters
Social rank is maintained through habitual subordination of those in lower
Threats and occasional punishment handed out to those of higher rank
reinforce the relationship
Organization stabilizes and formalizes intraspecific competitive relationships and
resolves disputes with a minimum of fighting and wasted energy
Social dominance can play a role in population regulation-- when it affects reproduction
and survival in a density-dependent manner
EX- wolf pack mating
Alpha female mates with alpha male
Each pack has one reproducing pair and one litter of pups each year
Reproducing pair gets priority in terms of the distribution of food
At high pack density and low food availability, individuals may be
expelled or leave the pack
At high wolf densities-- mortality increases and birth rates decline
Low wolf populations-- sexually mature males and females leave the pack, settle
in an unoccupied habitat, and establish their own packs with alpha females
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11.10- Territoriality Can Function to Regulate Population Growth
Home range- the area that an animal normally uses during a year
Size of home range varies with the availability of food resources, mode of food gathering,
body size, and metabolic needs
Mammalian species-- the home-range size is related to body size
Relationship between body size and energy requirements
Home range is not defended but could have aggressive interactions that influence the
movements of individuals into within another’s home range
If an animal defends any part of its home range it is called a territory
Defending a territory allows an individual to secure sole access to an area of habitat and
the resources it contains
Defense shows developed behavioral patterns
Song and call
Intimidation displays
Attack and chase
Marking with scents that evoke escape and avoidance in rivals
Number of territorial owners a habitat can support=total area available/the average size of
the territory
When the area is filled excess individuals are denied
Denied individuals make up the floating population of potential breeders
Territoriality as a function of population regulation
Only when there is an excess of males and females of reproductive age that are
unable to establish breeding territories
Increased population density resulted in increased competition and smaller territory size
for males that were successful in acquiring a territory
14.1- Predation Takes a Variety of Forms
Predation is more complex than a transfer of energy
Direct and complex interaction of two or more species: the eater and the eaten
A source of mortality- predator population has the potential to reduce or regulate the
growth of prey populations
As an essential resource- the availability of prey may function to regulate the predator
Predator or true predator- reserved for species that kill their prey more or less
immediately upon capture
Typically consume multiple prey organisms and function as agents of mortality
on prey populations throughout their lifetimes
Most herbivores only consume part of the plant-- usually does not end in mortality for the
Parasites feed on the prey organism (the host) while it is still alive
Harmful, but not lethal in the short term
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