Population Ecology
Environment: the conditions that surround an organism, consisting of both living and non-living components.
Habitat: where a particular population or community lives.
Niche: where an organism is found and what it does there.
Abundance: how many organisms are found in an area.
Distribution: whereabouts organisms may be found in a particular area.
A population is a group of individuals of a single species that live in the same general area Members of a population rely on the same resources, are influenced by similar environmental factors, and have a high likelihood of interacting with and breeding with one another. Populations can evolve through natural selection acting on heritable variations among individuals and changing the frequencies of various traits over time.
The density of a population is measured as the number of individuals per unit area or volume. The dispersion of a population is the pattern of spacing among individuals within the geographic boundaries. Measuring density of populations is a difficult task.
Density results from dynamic interplay between processes that add individuals to a population and those that remove individuals from it. Additions to a population occur through birth (including all forms of reproduction) and immigration (the influx of new individuals from other areas). The factors that remove individuals from a population are death (mortality) and emigration (the movement of individuals out of a population). I
Dispersion is clumped when individuals aggregate in patches This is the most common type of dispersion in populations Plants and fungi are often clumped where soil conditions favor germination and growth. Animals may clump in favorable microenvironments (such as isopods under a fallen log) or to facilitate mating interactions. Group living may increase the effectiveness of certain predators, such as a wolf pack.
Indicator species: if a species is thriving and/or out-competing other species in a particular habitat, it indicates that conditions in that habitat are the optimum for that species, i.e. a presence of this species gives an indication as to conditions. The species in question is known as an indicator species.
Population growth: populations are dynamic, and are subject to change over a period of time, as described by a sigmoid growth curve.
Indicator species: if a species is thriving and/or out-competing other species in a particular habitat, it indicates that conditions in that habitat are the optimum for that species, i.e. a presence of this species gives an indication as to conditions. The species in question is known as an indicator species.
Population growth: populations are dynamic, and are subject to change over a period of time, as described by a sigmoid growth curve.
Population growth under ideal conditions is exponential
Habitat: where a particular population or community lives.
Niche: where an organism is found and what it does there.
Abundance: how many organisms are found in an area.
Distribution: whereabouts organisms may be found in a particular area.
A population is a group of individuals of a single species that live in the same general area Members of a population rely on the same resources, are influenced by similar environmental factors, and have a high likelihood of interacting with and breeding with one another. Populations can evolve through natural selection acting on heritable variations among individuals and changing the frequencies of various traits over time.
The density of a population is measured as the number of individuals per unit area or volume. The dispersion of a population is the pattern of spacing among individuals within the geographic boundaries. Measuring density of populations is a difficult task.
Density results from dynamic interplay between processes that add individuals to a population and those that remove individuals from it. Additions to a population occur through birth (including all forms of reproduction) and immigration (the influx of new individuals from other areas). The factors that remove individuals from a population are death (mortality) and emigration (the movement of individuals out of a population). I
Dispersion is clumped when individuals aggregate in patches This is the most common type of dispersion in populations Plants and fungi are often clumped where soil conditions favor germination and growth. Animals may clump in favorable microenvironments (such as isopods under a fallen log) or to facilitate mating interactions. Group living may increase the effectiveness of certain predators, such as a wolf pack.
Indicator species: if a species is thriving and/or out-competing other species in a particular habitat, it indicates that conditions in that habitat are the optimum for that species, i.e. a presence of this species gives an indication as to conditions. The species in question is known as an indicator species.
Population growth: populations are dynamic, and are subject to change over a period of time, as described by a sigmoid growth curve.
- Competition is the interaction of different organisms for the same resources. There are two types of competition:
- Intraspecific competition occurs between members of the same species.
- Interspecific competition occurs between members of different species. One consequence of this type of competition is summarised by Gause’s Competitive Exclusion Principle, which states that if two species occupy the same ecological niche, the interspecific competition leads to the extinction of one or the other of the species.
- Predation: as a prey population increases, the number of individuals preyed upon naturally increases, but the percentage of individuals preyed upon decreases. This is because prey must be caught, eaten and digested- a process which takes a set amount of time. Therefore, even though more prey is available, time constraints and the fact that predators will only hunt what they need to survive, means that the percentage of prey caught is lower.
Indicator species: if a species is thriving and/or out-competing other species in a particular habitat, it indicates that conditions in that habitat are the optimum for that species, i.e. a presence of this species gives an indication as to conditions. The species in question is known as an indicator species.
Population growth: populations are dynamic, and are subject to change over a period of time, as described by a sigmoid growth curve.
Population growth under ideal conditions is exponential
- Lag phase: Birth rate exceeds death rate but population increase is slow because there are few organisms available to reproduce.
- Exponential phase: Rapid population increase. Short doubling time means population doubles at regular intervals, barring any limiting factors.
- Stationary phase: birth rate equals death rate, so no further population growth possible. Population has reached carrying capacity- one or more factors have become limiting.
- Death phase: death rate exceeds birth rate. A vital factor has become severely limited, leading to death from lack of vital nutrients or an excess of toxic substances.
Exponential growth cannot continue forever because typically, resources are limited. As population density increases, each individual has access to an increasingly smaller share of available resources. Ultimately, there is a limit to the number of individuals that can occupy a habitat, known as carrying capacity. Carrying capacity is not fixed but varies over space and time with the abundance of limiting resources.
Population limiting factors are defined as Density-dependent factors have an increased effect on a population as population density increases. This is a type of negative feedback. Interspecific competition and predation can reduce reproductive output. Example: As a prey population builds up, predators may feed preferentially on that species, consuming a higher percentage of individuals. Resource (water, food, territory) availability is a very significant limiting factor. Example: The presence of non-breeding individuals in a population of plovers is an indication that territoriality is restricting population growth. The accumulation of toxic wastes can also contribute to density-dependent regulation of population size.
Another factor is known as Density-independent factors are unrelated to population density. Abiotic factors such as weather, climate and fire are examples It doesn’t matter how many individuals there are, if there is a heavy snowfall, a hurricane or a fire, all organisms in the vicinity will be impacted.
Natural selection favors traits that improve an organism’s chances of survival and reproductive success. In every species, there are trade-offs between survival and traits such as frequency of reproduction, number of offspring produced, size of offspring produced and investment in parental care. Organisms have finite resources, and limited resources mean trade-offs. Life histories represent an evolutionary resolution of several conflicting demands. Based on these pressures, organisms have evolved different reproductive strategies.
Population limiting factors are defined as Density-dependent factors have an increased effect on a population as population density increases. This is a type of negative feedback. Interspecific competition and predation can reduce reproductive output. Example: As a prey population builds up, predators may feed preferentially on that species, consuming a higher percentage of individuals. Resource (water, food, territory) availability is a very significant limiting factor. Example: The presence of non-breeding individuals in a population of plovers is an indication that territoriality is restricting population growth. The accumulation of toxic wastes can also contribute to density-dependent regulation of population size.
Another factor is known as Density-independent factors are unrelated to population density. Abiotic factors such as weather, climate and fire are examples It doesn’t matter how many individuals there are, if there is a heavy snowfall, a hurricane or a fire, all organisms in the vicinity will be impacted.
Natural selection favors traits that improve an organism’s chances of survival and reproductive success. In every species, there are trade-offs between survival and traits such as frequency of reproduction, number of offspring produced, size of offspring produced and investment in parental care. Organisms have finite resources, and limited resources mean trade-offs. Life histories represent an evolutionary resolution of several conflicting demands. Based on these pressures, organisms have evolved different reproductive strategies.
Here is video to give you a more visual of population ecology
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