75 terms

APES Chapter 6 ⟺ Population and Community Ecology

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Population
The individuals that belong to the same species and live in a given area at a particular time
Community
All of the populations of organisms in a given area
Ecosystem
The flow of energy and matter: biotic and abiotic components together in a specific area
Biosphere
Earth and its global processes
Population ecology
The study of factors that cause populations to increase or decrease
Population size (N)
The total number of individuals within a defined area at a given time
Population density
The number of individuals per unit area (or volume in the case of aquatic organisms) at a given time
Population distribution
A description of how individuals are distributed with respect to one another. There are three types: (1) random (2) Uniform [trees at a plantation] (3) clumped [predator protection]
Sex ratio
The ratio of males to females in a population
Age structure
A description of how many individuals fit into particular age categories in a population
Limiting resource
A resource that a population cannot live without and that occurs in quantities lower than the population would require to increase in size
Density-dependent factor
A factor that influences an individual's probability of survival and reproduction in a matter that depends on the size of the population (Ex: food)
Carrying capacity (K)
The limit of how many individuals in a population the environment can sustain
Density-independent factor
A factor that has the same effect on an individual's probability of survival and the amount of reproduction at any population size (Ex: natural disaster)
Explain how nature exists at several levels of complexity
Nature exists at several levels of complexity: individuals, populations, communities, ecosystems, and the biosphere
Discuss the characteristics of populations
Populations can have distinct population sizes, densities, distributions, sex ratios, and age structures
Contrast the effects of density-dependent and density-independent factors on population growth
Density-dependent factors influence an individual's probability of survival and reproduction in a manner that is related to the size of the population. Density-independent factors have the same effect on an individual's probability of survival and reproduction in populations of any size.
Population growth models
Mathematical equations that can be used to predict population size at any given moment in time
Population growth rate
The number of offspring an individual can produce in a given time period, minus the deaths of the individual or its offspring during the same period
Intrinsic growth rate (r)
The maximum potential for growth of a population under ideal conditions with unlimited resources (more resources = more opportunity to reproduce)
Exponential growth model
A growth model that estimates a population's future size (N↓t) after a period of time (t), based on the intrinsic growth rate (r) and the number of reproducing individuals currently in the population (N↓0)
J-shaped curve
The curve of the exponential growth model when graphed
Logistic growth model
A growth model that describes a population whose growth is initially exponential, but slows as the population approaches the carrying capacity of the environment
S-shaped curve
The shape of the logistic growth model when graphed
Overshoot
When a population becomes larger than the environment's carrying capacity (Ex: animals produce offspring in accordance to the amount of food that existed at the time of mating, if the individuals produced more offspring than could be sustained at the time of year they were born, the population will experience an overshoot and a die-off -> mate fall/winter, born in spring)
Die-off
A rapid decline in a population due to death
Population oscillations around carrying capacity example
K-selected species
A species with a low intrinsic growth rate that causes the population to increase slowly until it reaches carrying capacity (remember because "K" is the variable used for carrying capacity)
Traits of K-selected species
Typically large, population size always relatively close to carrying capacity in ideal situations, reach reproductive age late, produce a small number of large offspring, give substantial parental care, long life span, few reproductive events, slow population growth rate, density-dependent population regulation, and stable population dynamics.
Example: elephants, other large mammals, and most birds
r-selected species
A species that has a high intrinsic growth rate (remember because "r" is the variable for intrinsic growth rate), which often leads to population overshoots and die-offs
Traits of r-selected species
Reproduce often, normally aren't remaining near carrying capacity, produce a large number of small offspring, they have a cycle of rapid population growth which leads to overshoots and die-offs, normally small animals, reach reproductive age quickly, provide little to no parental care, short life span, lots of reproductive events, fast population growth rate, density-independent population regulation, and unstable population dynamics.
Example: mice, small fishes, insect species, weedy plants, and other pests
K-selected and r-selected species are on opposite sides of the.....
Reproductive spectrum.
Many animals possess reproductive traits from both sides.
Survivorship curve
A graph that represents the distinct patterns of species survival as a function of age
Type I survivorship curve
A pattern of survival over time in which there is high survival throughout most of the life span, but then individuals start to die in large numbers as they approach old age (Ex: K-selected species)
Type II survivorship curve
A pattern of survival over time in which there is a relatively constant decline in survivorship throughout most of the life span (Ex: corrals and squirrels to name a few)
Type III survivorship curve
A pattern of survival over time in which there is low survivorship early in life with few individuals reaching adulthood (Ex: r-selected species)
Corridor
Strips of natural habitat that connect populations (Ex: populations of the same species in close proximity that live in different communities, but are connected through these strips)
Metapopulation
A group of spatially distinct populations that are connected by occasional movements of individuals between them (This connection allows populations to persist by introducing genetic diversity and the possibility of higher numbers to small, endangered populations and also through making a stem for more populations in places where previous populations have died out from any variety of causes and there is available land)
Inbreeding depression
When individuals with similar genotypes--typically relatives--breed with each other and produce offspring that have an impaired ability to survive and reproduce (The impaired ability to survive and reproduce is caused by a genetic mutation. Since a small population has less genetic diversity and there is a strong possibility of relatives mating, if two relatives that have a copy of this mutation mate, there is a very high chance of their offspring having two copies of the mutation and not being able to survive and reproduce sufficiently)
Explain the exponential growth model of populations, which produces a J-shaped curve
The exponential growth model describes rapid growth under ideal conditions when resources are not limited. The J-shaped curve occurs because the population initially grows slowly when few individuals are present to reproduce but then grows rapidly as the number of reproducing individuals increases
Describe how the logistic growth model incorporates a carry capacity and produces an S-shaped curve
The logistic growth model incorporates density-dependent factors that allow rapid initial growth but then cause population growth too slow down as populations approach their carrying capacity. When we allow lag times between when resources change in abundance and when populations produce new offspring, we can observe population overshoots and die-offs
Compare the reproductive strategies and survivorship curves of different species
Organisms have a range of reproductive patterns. At the extremes are r-selected species, which experience rapid population growth rates, and K-selected species, which experience high survivorship and slow population growth rates. Patterns of survivorship over the life span can be graphically represented as type I, II, and III survivorship curves
Explain the population dynamics that occur in metapopulations
Metapopulations are groups of spatially distinct populations that are connected by occasional movement of individuals. These movements reduce the probability of any of the populations going extinct.
Community ecology
The study of interactions between species
Symbiotic relationship
The relationship between two species that live in close association with each other
Interactions between species and their effects
Competition
The struggle of individuals to obtain a shared limiting resource (Look at book for Gause experiment example of the two aquatic organisms competing together and thriving alone)
Competitive exclusion principle
The principle stating that two species competing for the same limiting resource cannot coexist (One species will perform better and one will go extinct)
Resource partitioning
When two species divide a resource based on differences in their behavior or morphology (Natural selection favoring individuals that overlap less with other species' resources, aka the better competitor wins and the loser either fails and dies out due to poorer survival and reproduction or fails and evolves to need different resources)
Temporal resource partitioning
A strategy to reduce overlap in which two species use that same resource but at different times
Spatial resource partitioning
If two species reduce competition by using different habitats (Ex: cactus root length variation and birds using different sections of a tree to hunt)
Morphological resource partitioning
The evolution if differences in body size of shape in species to reduce competition (Ex: finches with varying beak sizes in the Galápagos)
Predation
An interaction in which one animal typically kills and consumes another animal (Ex: lions and gazelles)
Parasitoid
A specialized type of predator that lays eggs inside other organisms (referred to as its host; Ex: wasps and flies)
What are the types of defense mechanisms that prey employ to defend against predators?
Parasitism
An interaction in which one organism lives on or in another organism (the host)
Pathogen
A parasite that causes disease in its host (Ex: viruses, bacteria, fungi, protists, and helminths)
Herbivory
An interaction in which an animal consumes a producer (AKA herbivores eating plants)
Mutualism
An interaction between two species that increases the chances of survival of reproduction for both species (Ex: the relationship between plants and their pollinators)
Commensalism
A relationship between species in which one species benefits and the other species is neither harmed or helped (Ex: birds using tree branches to perch upon)
Keystone species
A species that plays a far more important role in its community than its relative abundance might suggest
Characteristics of keystone species
Usually not the most abundant species or main energy producers, may be predators, sources of food, mutualistic species, or providers of some essential service
Ecosystem engineer
A keystone species that creates or maintains habitat for other species (Ex: beavers)
Identify species interactions that cause negative effects on one or both species
- Competition is an interaction between two species that share a limiting resource. Over time, competition for a resource can cause natural selection to favor those individuals that have reduced overlap in resource use and this can lead to spatial, temporal, or morphological resource partitioning.
- Predation is an interaction in which animals partially or entirely consume another animal. Predators can affect the abundance of prey populations and cause the evolution of anti-predator defenses in prey populations.
- Parasitism is an interaction in which one organism lives on or in another organism known as the host. Those parasites that can cause disease in their hosts are called pathogens.
-Herbivory is an interaction in which animals consume producers. In some cases, herbivores can have dramatic effects on plant and agal communities by removing the most palatable (tasty) species.
Discuss species interactions that cause neutral or positive effects on both species
- Mutualisms are interactions that benefit two interacting species by increasing the chances of survival or reproduction for both. One of the most common mutualisms is the interaction between flowering plants and their pollinators. A second well-known mutualism is between acacia trees and the ants that defend the trees in exchange for food and a place to live.
-Commensalisms are interactions in which one species benefits but the other is neither harmed nor helped. Examples include birds perching on trees and marine fish using corral reefs for protection from predators.
Explain the role of a keystone species
Keystone species play a role in the community that is far more important than its relative abundance might suggest. Common examples include predators that alter the outcome of competition in intertidal communities and beavers that create large ponds by constructing dams on streams.
Ecological succession
The predictable replacement of one group of a species by another group of species over time
Primary succession
Ecological succession occurring on surfaces that are initially devoid of soil (Ex: community forming on bare rock left behind by natural events)
Secondary succession
The succession of plant life that occurs in areas that have been disturbed but have not lost their soil (follows an event where vegetation is taken but soil is still intact)
Pioneer species
A species that can colonize new areas rapidly and grow well in full sunshine (Ex: Apsen tree)
Theory of island biogeography
A theory that demonstrates the dual importance of habitat size and distance from a colonizing species in determining species richness (Used first with a islands, but now considered when designating "islands" or natural habitat for the purpose of conservation)
Explain the process of primary succession
Primary succession occurs on surfaces that are initially devoid of soil, such as bare rock that is exposed after the retreat of glaciers or the cooled lava from a volcanic eruption. Over time, plants and animal arrive at the site and modify the environment, making it more favorable for other species to arrive and persist.
Explain the process of secondary succession
Secondary succession occurs in areas that have been disturbed but have not lost their soil. A common example is the bare soil left behind when farmers stop planting crops in a field. Over time, plants and animals colonize the site, alter the environmental conditions, and favor the persistence of other species.
Explain the process of aquatic succession
Lakes and ponds experience sedimentation over long periods of time and this slowly fills in the basin. Over thousands of years, the lakes and ponds can be slowly converted into terrestrial habitats.
Describe the factors that determine the species richness of a community
The species richness of a community is typically higher at latitudes that are closer to the equator. Richness is also higher in older sites where evolution has been producing new species for longer periods of time. Finally, more species exist in larger habitats and habitats that are closer to sources of new species, as is the case for oceanic islands that are located close to continents.