Summary study material Behavioural Biology Chapter 4,8,11 of the book "Animal Behavior; Concepts, methods and applications (3rd edition; 2021)", given in the course Behavioural Biology, 2021/2022.
Chapter 11: Habitat selection, territoriality and aggression
Resource availability and the presence of others can influence habitat selection.
In nature, variation in the density of individuals in different habitat locations is common. Two
factors help explain much of this variation:
- The amount of resources. Resource availability is an important aspect of habitat quality
- The number of other individuals in a habitat. This affects the level of competition for
those resources.
Important factor that is important in distribution of animals over habitat is access to resources.
- It is important aspect of habitat quality
- Access to resources is crucial for the survival
- Reproduction and there will be competition over limited resources.
The ideal free distribution model: explains how animals distribute themselves among habitats
→ assumes that animals act in an ‘ideal’ manner → means that they select habitats that
maximise fitness and are ‘free’ to enter any habitat → according to IFD: proportion of animals
over an habitat is proportional to the proportion of limiting resources per habitat.
Five assumptions made by IFD:
1. Individuals try to maximize their fitness
2. Individuals have equal competitive abilities
3. Individuals can move freely between patches at no cost
4. Individuals know where the best patch is
5. Fitness benefits of patch declines with number of competitors
The IFD model makes 2 predictions:
- Number of individuals in each habitat will be proportional to habitat
quality, resulting in more animals settling in higher-quality habitats.
- All animals will have the same fitness no matter where they settle
The IFD allows us to make predictions about the relative number of individuals in each habitat
→ the number of individuals in a habitat will be proportional to the resources available. During
the settling process, individuals are always free to move to a higher-quality habitat if one is
available. When the individuals have settled, none can obtain a higher fitness by moving to a
new habitat.
Experiment in which ideal free distribution is tested:
Distribution of sticklebacks → prof. Put food in a 2:1 ratio over different patches. Patch A with 2
food over B had double the amount of fish. After x amount of time, the amount of food was
switched. After a period of time patch B had double the amount of fish relative to A.
, Territoriality
- Individuals may defend resources
- Territory: area defended to obtain exclusive access to resources
- Territorial behavior limits population density
Floaters: when both rich and poor habitats are full, floaters will move
between the different habitats in search of food.
Territorial defence is often costly: territorial defence is energetically
expensive, so only males with high energy reserves can successfully
defend their territory. Territorial males have much higher fat storage
than non territorial males.
Conspecific attraction: the IFD model assumes that competition for resources results in a
decline in individual fitness as the number of individuals in a habitat increases. Therefore new
settlers should avoid rivals if a better option exists. However, sometimes individuals exhibit a
pattern of settling near other individuals = conspecific attraction.
2 hypothesis for the explanation of conspecific attraction:
1. Allee effect: when population size is low, fitness increases with density → examples:
solitary individuals may be at high risk for predation, mates can be found more easily in a
group.
2. Conspecific cueing: because habitat quality is a function of many factors, it may be
difficult to assess. Therefore the presence of other individuals is a cue that the location
has high qualities.
Individual condition and environmental factors affect territoriality
Territory: an area defended to obtain the exclusive use of the resources it contains. However, it
also requires that animals expend effort to defend these resources from rivals. Territories differ
from home ranges = areas of repeated use that are not defended. Home ranges of many
individuals can overlap, while territories do not.
Territory defense requires physical effort: it takes both time and energy to chase off intruders.
Aggressive behaviours involved in territorial defense require substantial effort, and so only
individuals in good body condition may be able to acquire and defend territory. Body condition
can be measured by body mass, body size or fat, which indicates extra energy storage that
could be used in intense behavioural interactions.
Hormone influence aggression
Contests over resources involve a variety of aggressive behaviours, including chasing, pushing,
wrestling and fighting. Some species defend their territory year-round, while others defend a
territory only during the breeding season. This results in aggression level differences between
these animals.
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