Community Ecology Flashcards
What is an ecological niche?
The role that an organism plays in an ecosystem - it is defined by the range of conditions and resources within which an organism can live:
- Conditions: physical attributes of the environment like temperature, salinity, humidity, etc…
- Resources: substances used and consumed by the organisms like food, water, nesting sites, etc…
A niche is a species’ way of life in a community and includes everything that affects its survival and reproduction, such as how much water and sunlight it needs, how much space it requires, and the temperatures it can tolerate. A species’ niche should not be confused with its habitat, which is the place where it lives. Its niche is its pattern of living.
Fundamental vs realized niche
Fundamental niche consists in the full range of conditions and resources that an organism could theoretically use in the absence of competition with other species.
Realized niche: the portion of the fundamental niche that an organism actually occupies. Species occupy just a portion of their theoretical ecological niche because there is a partial overlapping with different species, which leads to competition.
Generalist vs specialist species
In terms of ecological niche, species can be classified into:
generalists: species with broad niches, like cockroaches, and may have advantages when environmental conditions change.
Specialist: species with narrow niches, like pandas, that may have advantages when environmental conditions are stable over time (tropics).
General types of species
Native species: species that normally live and thrive in a particular ecosystem.
Non-native or alien species: species that originate in other ecosystems and enter an ecosystem by migration or by voluntary or involuntary introduction by humans.
Keystone species: species that play a critical role in an ecosystem. They are not necessarily dominant in terms of biomass but play a fundamental role. A loss of a keystone species shuts down the ecosystem.
What are the main types of species interactions?
Major types of biotic interactions are:
- interspecific competitions: two or more species use the same limited resource and adverseley affect each other.
- Predation: members of one species (predator) feeds on another species (prey).
- Symbiosis: a long-lasting relationship in which species live together in intimate association. Different types of symbiotic interactions are:
a) Parasitism: one organism (parasite) lives on part of another organism (host).
b) Commensalism: one organism benefits from another but neither helps nor harms the other organism.
c) mutualism: two species interacting in a way that benefits both.
What are the main types of species interactions?
Major types of biotic interactions are:
- interspecific competitions: two or more species use the same limited resource and adverseley affect each other.
- Predation: members of one species (predator) feeds on another species (prey).
- Symbiosis: a long-lasting relationship in which species live together in intimate association. Different types of symbiotic interactions are: parasitism, mutualism, commensalism
Explain the Lotka-Volterra model
The Lotka–Volterra model is frequently used to describe the dynamics of ecological systems in which two species interact, one a predator and one its prey. The model is simplified with the following assumptions: (1) only two species exist: fox and rabbit; (2) rabbits are born and then die through predation or inherent death; (3) foxes are born and their birth rate is positively affected by the rate of predation, and they die naturally.
The characteristic of this model is that the population change of the predator and the prey are explained in terms of each other. The size of the fox population has a negative effect on the rabbit population, and the size of the rabbit population has a positive effect on the fox population. The Lotka–Volterra model can be described using a pair of first-order, nonlinear, differential equations as follows:
dR=dt ¼ rabbit birth rate R – rabbit death rate R F
dF=dt ¼ fox birth rate R F – fox death rate F
where R and F are the population of rabbit and fox, respectively.
Explain the principle of competitive exclusion
The competitive exclusion principle says that two species can’t coexist if they occupy exactly the same niche (competing for identical resources). Two species whose niches overlap may evolve by natural selection to have more distinct niches, resulting in resource partitioning.
What is resource partitioning?
It is the division of limited resources by species to help avoid competition in an ecological niche. In any environment, organisms compete for limited resources, so organisms and different species have to find ways t coexist with one another. Species with similar resource requirements can coexist because they use limited resources at different times, in different ways, or in different places. For example, specialized feeding niches of various birds of coastal wetland enable coexistence of many species. Competition is reduced because animals prefer to partition their resources.
Main characteristics of predatory-prey relationship
In predation, a member of one species (the predator) feeds directly on all or part of a living organism of another plant or animal species (the prey) as part of a food web. Together, the two different species, such as lions (the predator or hunter) and zebras (the prey or hunted), form a predator–prey relationship.
Predators evolve characteristics for efficient capture of prey like keen eyesight, speed, etc), while preys evolve characteristics to avoid being eaten like camouflage, chemical defenses, etc. As predators evolve, so do their preys - coevolution. Predators promote diversity by keeping competition in check.
In a predator-prey relationship the two populations have opposite effects on one another. At the individual level, members of the predator
species benefit and members of the prey species are
harmed. At the population level, predation plays a role in evolution by natural selection. Animal predators, for example, tend to kill the sick, weak, aged, and least fit members of a population because they are the easiest to catch. This leaves behind individuals with better defenses against predation. Such individuals tend to survive longer and leave more offspring with adaptations that can help them avoid predation. Thus, predation can help increase biodiversity by promoting natural selection in which species evolve with the ability to share limited resources by reducing their niche overlap.
Main characteristics of the cooperation and mutualism relationship
This type of relationship can be intra or interspecies. Mutualism is the highest level of cooperation since both species benefit from it: it is an interaction that benefits both species by providing each with food, shelter, or some other resource. For example, honeybees, caterpillars, butterflies, and other insects feed on a male flower’s nectar, picking up pollen in the process, and then pollinating female flowers when they feed on them.
Mutualism can be obligatory: when two organisms cannot live without each other. For example In gut inhabitant mutualism: vast armies of bacteria
in the digestive systems of animals help to break down (digest) their hosts’ food. In turn, the bacteria receive a sheltered habitat and food from their host. Hundreds of millions of bacteria in your gut secrete enzymes that help digest the food you eat.
Main characteristics of the commensalism relationship
Commensalism is an interaction that benefits one species but has little, if any, effect on the other. For example, in tropical forests certain kinds of silverfish in-
sects move along with columns of army ants to share the food obtained by the ants in their raids. The army ants receive no apparent harm or benefit from the silverfish.
Another example involves plants called epiphytes which attach themselves to the trunks or branches of large trees in tropical and subtropical forests. These air plants benefit by having a solid base on which to grow. They also live in an elevated spot that gives them better access to sunlight, water from the humid
air and rain, and nutrients falling from the tree’s upper leaves and limbs. Their presence apparently does not harm the tree.
Explain symbiotic species interaction - parasitism
Parasitism occurs when one organism (the parasite) feeds on the body of, or the energy used by, another organism (the host), usually by living on or in the host.
Parasitism can be viewed as a special type of predation wherein the parasite:
- is usually smaller than the prey
- remains closely associated with the prey over time
- rarely kills its host
Some parasites, such as tapeworms and some disease-causing microorganisms (pathogens), live inside their hosts. Other parasites attach themselves to the outsides of their hosts.
Like predator–prey interactions, parasite–host interactions can lead to coevolutionary change. For example, malaria is caused by a parasite spread by the bites of a certain mosquito species. The parasite invades red blood cells, which are destroyed every few days when they are swept into the spleen. However, through coevolution, the malaria parasite developed an adaptation that keeps it from being swept into the spleen. The parasite produces a sticky protein nodule that attaches the cell it has infected to the wall of a blood vessel.
What is a community?
A community, or biological community, consists of all the populations of different species that live in a particular place. For example, a catfish species in a pond usually shares the pond with other fish species, and with plants, insects, ducks, and many other species that make up the community. Many of the organisms in a community interact with one another in feeding and other relationships.
What is a trophic cascade?
Trophic cascade, an ecological phenomenon triggered by the addition or removal of top predators and involving reciprocal changes in the relative populations of predator and prey through a food chain, which often results in dramatic changes in ecosystem structure and nutrient cycling.
In a three-level food chain, an increase (or decrease) in carnivores causes a decrease (or increase) in herbivores and an increase (or decrease) in primary producers such as plants and phytoplankton.
