Download 12.5 - Interactions between Individuals

UNIT 5: Population Dynamics
12.5: Interactions between Individuals
pg. 616 - 628
In ecosystems, species form populations, there are more then on species
living in an ecosystem, therefore there are many populations. These
populations interact and form communities: therefore there are intraspecific
and interspecific relationships occurring. These interactions can be
beneficial, harmful, or neutral, may or may not affect the individual’s ability
to survive or reproduce, and is a product of long-term evolutionary
adaptation.
When individuals of two different species exert selective pressures
(reproductive success) on each other, influencing their evolution is known as
coevolution.
Co-evolution – is a process in which one species evolves in response to the
evolution of another species.
Co-evolutionary relationships can take on many forms, for example:
Predation – is the interaction between a predator and a prey where the
predator gains nutrients and energy form the prey while killing it.
Herbivory – is the interaction between herbivorous animals and the plants
that they eat.
Mutualism – is an interaction n which both partners benefit.
Parasitism – is an interaction in which on species benefits and the other is
harmed.
Commensalism – is an interaction in which one species benefits and the
other is unaffected.
Table 1: Population Interactions and their Effects
Interaction
Effects on Inte4racting
Example
Populations
Predation
Herbivory
Mutualism
Parasitism
+/- Predators gain nutrients and
energy; prey are killed or injured
+/- Herbivores gain nutrients and
energy; plants are killed or injured
+/+ Both populations benefit
+/- Parasites gain nutrients; hosts
are injured or killed
-/- Both competing populations
lose access to some resources
Commensalism -/0 One population benefits; the
other is unaffected
Competition
Northern lynx (predator) and
snowshoe hare (prey)
White-tailed deer (herbivore) and
foliage
Honey bee (pollinator) and
flowering plants
Mistletoe, which attaches to a tree
and takes water and nutrients
from its host; usually stunts
growth but can kill the tree with
heavy infestation
Trees in a forest competing for
light
Moss, which grows on a tree,
getting the light and nutrients it
needs while the tree is unaffected
Predation and Herbivory
Feeding relationships, food chain, and food webs indicate the movement of
nutrients and energy from producer through to top carnivore. Animals
acquire their nutrients and energy by consuming other organisms, predation
and herbivory are factors of co-evolution, which has allowed predators and
herbivores to evolve characteristics that enable them to feed effectively.
Food abundance affects food choice. If a prey is scares, then the predator
will take what it can get, creating a higher cost-to-benefit ratio. If there is an
abundance of food then, the predator will specialize, and select prey with
largest energy return.
Defence Mechanisms
Defence mechanisms include camouflage, behavioural defences, chemical
defences, spines and armour, and mimicry. Any adaptation that is used by
prey increases its chance of survival, giving the prey an advantage against its
predators.
Camouflage allows an organism to mimic the patterns of its environment,
making it hard to be identified by its predator
Behavioural defences can passive or active. Standing still is a passive
approach while fleeing is an active response.
Chemical defences make the organism unattractive to the predator. The prey
can release noxious odours or releasing poisonous chemicals.
Spine and Armour, are used by some plants and animals. The use of hard
thorny like structures prevents the predator from harming its prey.
Mimicry occurs when an organism mimics another organism which the
predator finds unpalatable. There are two types of mimicry; Batesian and
Mullerian. Batesian, a palatable organism mimics an organism which in
unpalatable. For Mullerian, two or more unpalatable organisms that share
common predators mimic each other.
Mimicry – is a form of defense in which one species evolves an appearance
that resembles the appearance of another species.
Population Cycles
A predator prey relationship is an interspecific interaction and dependent on
the density of population. As the density of the prey population increases, so
will the predator population follow, since there is more food to support an
increase. As the prey population decreases through over feeding, the
predator population will decrease because of lack of resources and an
increase in competition for those resources.
The populations will be dynamic and continue to fluctuate. There is a lag in
response, the prey population will either increase or decrease and the
predator population will lag in responding to these changes.
There are other factors that can affect the cycling of a population, such as;
catastrophic natural events, changes in climate, and human interference,
non-native species introduction and habitat loss.
Figure 4: a) A model of the predator-prey cycle; b) Lynx and hare populations through time.
Competition
When different species use the same limiting resources will experience
interspecific competition, this type of interaction will increase mortality
rates and decrease reproduction. Population size and growth rates of each of
the competing species populations are reduced over time.
There are two main forms of interspecific competition: interference
competition and exploitative competition.
Interference Competition –is competition in which all the individuals have
equal access to resources; the fitness of some individuals is reduced by the
presence of others.
Exploitive Competition – is competition in which all the individuals have
equal access to resources; some have superior ability to gather resources.
Biological fitness, also called Darwinian fitness, means the ability to survive
to reproductive age, find a mate, and produce offspring. Basically, the more
offspring an organism produces during its lifetime, the greater its biological
fitness.
Competition and Niches
Alfred J. Lotka and Vito Volterra both proposed a model of interspecific
competition, independently, describing the effects of competition between
two species, where if one specie increased in population size, it would
negatively affect the growth rate of the other species.
G.F. Gause, tested the model experimentally, using two different specie of
Paramecium; aurelia and caudatum. He grows each paramecium species in
separate cultured medium, controlling their environments similarly. Each
specie of paramecium showed rapid population growth until they met their
carrying capacity, than maintained population size.
Gause then mixed the two specie of Paramecium, aurelia and caudatum, in
one cultured medium. Aurelia competed with caudatum. The aurelia
population increased, while the caudatum population did not. He identified
the results as the Competitive Exclusion Principle.
”Populations of two or more specie can not coexist indefinitely if they rely
on the same limiting resources and exploit these resources in the same way.
One species inevitably harvests resources more efficiently; (fitness)
produces more offspring than the other, and by its actions, negatively affects
the other species.”
Ecological niche is an organism’s biological characteristics, including use of
and interaction with abiotic and biotic resources in its environment. This
concept allows ecologists to visualize resource use and the potential for
interspecific competition in nature. The niche includes food, shelter, and
nutrients, as well as the abiotic conditions, such as light, and temperature.
Ecologists can study competition between two populations by plotting their
fundamental niches and realized niches, if their fundamental niches overlap,
then they may compete for resources.
Fundamental Niche – is the range of conditions and resources that a
population can possibly tolerate and use.
Realize Niche – is the range of conditions and resources that a population
actually uses in nature.
Figure 5: G.F. Gause performed experiments to observe interspecific competition in
Paramecium. a) and b) When each species was raised alone, both species reached a stable
population size, c) When the species were raised together, Paramecium aurelia persisted
while the population of Paramecium caudatum declined
Resource Partitioning
Resource Partitioning – is a situation in which several species that live in
the same place use different resources or use the same resources in different
ways.
Organisms may compete for resources, or they may avoid competition by
partitioning resources, which allows for the co-existence of different species
in the same ecosystem.
Figure 8: a demonstration of competition between two species of barnacles. A) Before the
experimental treatments, both species exist in their realized niches. B) In the absence of
Balanus, Chthamalus occupies both shallow water and deep water. C) In the absence of
Chthamalus, Balanus still occupies only deep water.
Symbiosis
In biology there are three types of symbiotic relationships recognized;
Mutualism, commensalism, and parasitism.
Mutualism (+/+) – both partners will benefit from their relationship, for
example the relationship between plants and insects. Bees support the
pollination of plants while the bees obtain the nectar secrete from the flower.
In this situation both organisms exploit each other for their common good.
Commensalism (+/0) – One partner benefits while the other neither benefits
or is harmed. Commensalism is rare in nature because the interaction
between two organisms rarely leaves one unaffected.
Parasitism (+/-) – During this type of interaction one organism will benefit
while the other is negatively affected, and receives no benefit. Parasitic
relationships could also be considered specialized predator – prey
relationships, one organism is feeding on the other.
Disturbing Ecosystem Relationships
Human activities, such as the introduction of non-native species and habitat
destruction are upsetting the dynamic equilibrium in many ecosystems.
The relationships between organisms in an ecosystem are dynamic,
organism compete for resources, are parts of food chains and food webs.
Interactions between two organisms will affect not only themselves but also
other species within the ecosystem.
The greatest disruption in an ecosystem is created by the introduction of a
non-native invasive species or the loss of a species. Non-native invasive
species enter an ecosystem where they do not have a natural predator to
control their population growth. The can disperse quickly, establish
themselves, and dominate the ecosystem. They will compete for limiting
resources, which will negatively impact native species, decreasing their
population or possible extinction.
Human impact, such as habitat destruction is currently ranked as the primary
cause of species extinction worldwide. Because of the interaction between
species in an ecosystem, when one organism becomes extinct it has a direct
impact on the entire ecosystem.
Chapter 12: Summary
pg. 632
Chapter 12: Self-Quiz
pg. 633
Chapter 12: Review
pg. 634 - 639