Ecology Exam 2 (Ch. 8 - 15)
Characterize the different types of interspecific competition:
(1) Consumption (2) Preemption (3) Overgrowth (4) Chemical interaction (5) Territorial (6) Encounter
Describe the three basic types of survivorship curves:
(1) when individuals tend to live out their physiological life span, survival rate is high throughout the life span, followed by heavy mortality at the end. With this type of survivorship pattern, the curve is strongly convex, or type 1. (2) If survivorship rates do not vary with age, the survivorship curve will be straight, or type 2. (3) If mortality rates are high in early life the curve is concave, or type 3.
Unitary and modular organisms:
A population is a group of individuals of the same species living in a defined area. Populations are characterized by distribution, abundance, density, and age structure. Most animal populations are made up of unitary individuals with a definitive growth form and longevity. In most plant populations, however, organisms are modular... These plant populations may consist of sexually produced parent plants and asexually produced stems arising from roots. A similar population structure occurs in animal species that exhibit modular growth.
Define a population:
A population is a group of individuals of the same species that inhabit a given area. By requiring that individuals be of the same species, the definition suggests the potential for interbreeding among members of the population. As such, the population is a genetic unit... It defines the gene pool, the focus of evolution. The population is a spatial concept, requiring a defined spatial boundary.
The primary factor influencing the distribution of a population is the occurrence of suitable environmental and resource conditions (habitat stability)...
A species with a geographically widespread distribution, such as red maple, is referred to as ubiquitous. In contrast, a species with a distribution that is restricted to a particular locality or localized habitat is referred to as endemic. Many endemic species have specialized habitat requirements.
Crude birthrate:
A standard convention in demography (the study of populations) is to express birthrates as births per 1000 individuals of a population per unit of time. This figure is obtained by dividing the number births that occurred during some period of time, typically a year, by the estimated population size at the beginning of the time period and multiplying the resulting number by 1000.
Abundance:
Abundance is defined as the number of individuals in a population. Abundance is a function of two factors: (1) the population density and (2) the area over which the population is distributed. Population density is the number of individuals per unit area or volume. Because landscapes are not homogeneous, not all of the area is suitable habitat. The number of organisms in available living space is the true or ecological density.
Determining a population's age structure requires some means of obtaining the ages of its members...
Age data for wild animals can be obtained in several ways, and the method varies with the species. The most accurate, but most difficult method, is to mark young individuals in a population and follow their survival through time. Other less-accurate methods include examining a representative sample of individual carcasses to determine their ages at death.
Once the age structure of a population has been determined, it can be represented graphically in the form of an age pyramid:
Age pyramids are snapshots of the age structure of a population at some period in time, providing a picture of the relative sizes of different age groups in the population. The age structure of a population is a product of the age-specific patterns of mortality and reproduction. A rectangle has no growth, a pyramid has positive growth, and an inverted pyramid has a negative growth rate.
Age-specific mortality and birthrates can be used to project population growth:
Age specific mortality rates (qx) from the life table together with the age-specific birthrates (bx) from the fecundity table can be combined to project changes in the population into the future - we can use this to construct a population projection table. Because females form the reproductive units of the population, we follow only females in constructing the table. N(t) = N(0)lambda ^ t r = ln (lambda)
In contrast to the model of declining rates of birth and survival with increasing population size, density-dependent mechanisms have also been identified that function to reduce rates of birth and survival at low population densities - referred to as the:
Allee effect. Small populations can be susceptible to a variety of factors tat directly influence the rates of survival and birth rate that result from life history characteristics related to mating, reproduction, and defense.
Life tables provide data for mortality and survivorship curves:
Although we can graphically display data from any of the columns in a life table, the two most common approaches are the construction of a mortality curved based on qx or a survivorship curve based on the lx column. Life tables and survivorship curves are based on data obtained from one population of the species at a particular time and under certain environmental conditions. They are like snapchats. For this reason, survivorship curves are useful for comparing on time, area, or sex with another.
Explain life history:
An organism's life history is its lifetime pattern of growth, development, and reproduction. Life history characteristics are traits that affect and are reflected in the life table of an organism.
To maximize contributions to future generations, an organism balances the benefits of immediate reproduction and future reproductive prospects, including the cost to fecundity (total offspring produced) and its own survival.
Another approach to reproduction is to initially invest all energy in growth, development, and energy storage, followed by one massive reproductive effort and then death. In this strategy, an organism sacrifices future prospects by expending all its energy in one suicidal act of reproduction. Organisms exhibiting this mode of reproduction are called semelparous.
Explain how stress may impact animals:
As a population reaches a high density, individual living space can become restricted. Often, aggressive contacts among individuals increase. One hypothesis of population regulation in animals is that increased crowding and social contact cause stress. Such stress triggers hormonal changes, that can suppress growth, curtail reproductive functions, and delay sexual activity. They may also suppress the immune system and break down white blood cells, increasing vulnerability to disease. Stress results in decreased births and increased infant mortality.
Differentiate between a metapopulation and a subpopulation:
As a result of environmental heterogeneity, most populations are divided into subpopulations, each occupying suitable habitat patches of various shapes and sizes within the larger landscape of unsuitable habitat. As a result, the population is divided into a group of spatially discrete local subpopulations. Ecologists refer to the collective of local subpopulations as a metapopulation. Although spatially separated, these local populations are connected through the movement of individuals among them.
Dispersal:
At some stage of their life cycles, most individuals are mobile. For some organisms, such as plants, dispersal is passive and dependent on various dispersal mechanisms. For mobile organisms, dispersal can occur for a variety of reasons, including the search for mates and unoccupied habitat. For some species, dispersal is a systematic process of movement between areas in a process called migration.
Intraspecific competition affects growth and development:
Because the intensity of intraspecific competition is usually density dependent, it increases gradually, and at first affects growth and development. Later, it affects individual survival and reproduction. As population density increases toward a point at which resources are insufficient to provide for all individuals in the population, some (contest competition) or all individuals (scramble competition) reduce their intake of resources...That reduction slows the rate of growth and development. The result is an inverse relationship between population density and individual growth, referred to as density dependent growth.
The primary factors driving the dynamics of population abundance are the demographic processes:
Birth and death.
The mating system of a species has direct relevance to its life history because it influences allocation to reproduction, particularly in males...
Competition among males for mates, courtship behavior, territorial defense, and parental care can represent a significant component of reproductive allocation. In addition, the degree of parental care has a direct effect on offspring survival. As such, a mating system is both influenced by and influences age-specific patterns of fecundity and mortality.
Intraspecific competition can impact mortality rates:
Competition for resources at high population densities can function to reduce survival. In turn, mortality functions to increase per capita resource availability, allowing for increased growth of the surviving individuals.
Intraspecific competition can reduce reproduction:
Competition within a population can reduce fecundity. The timing of the response depends on the nature of the population, and the mechanisms by which competition influences reproductive rate can vary with species.
K-selected species:
Competitive species Stable populations Long-lived Slower growth rate at low populations Maintain growth rate at high populations Cope with physical and biotic pressures Larger body size and slower development
Consumption competition:
Consumption interaction occurs when individuals of one species inhibit individuals of another by consuming a shared resource.
Population regulation involves density dependence:
Density dependent factors influence a population in proportion to its size. They function to slow the rate of population growth with increasing population density by increasing the rate of mortality (density-dependent mortality), decreasing the rate of fecundity (density-dependent fecundity), or both. Density dependent factors can also include patterns of predation or the spread of disease/parasites.
Sampling populations:
Determination of density and dispersion requires careful sampling and appropriate statistical analysis of the data. For sessile organisms, researchers often use sample plots. For mobile organisms, researchers use capture-recapture techniques or determine relative abundance using indicators of animal presence, such as tracks or feces.
Population dynamics:
Dispersal has the effect if shifting the spatial distribution of individuals and as a result the localized patterns of population density. Although the movement of individuals within the population results in a changing pattern of distribution and density through time, the primary factors driving the dynamics of population abundance are the demographic processes of birth and death.
Population distribution and density change in both time and space:
Dispersal has the effect of shifting the spatial distribution of individuals and consequently the localized patterns of population density. Emigration may cause density in some areas to decline, whereas immigration into other areas increases the density of subpopulations. In some cases, dispersal can result in the shift or expansion of a species' geographic range. In other cases, the range of expansion of a population has been associated with temporal changes in the environmental conditions, shifting the spatial distribution of suitable habitats.
Species interactions influence the species' niche:
Each species may be described in terms of the range of physical and chemical conditions under which it persists (survives and reproduces) and the array of essential resources it uses. This characterization of a species is known as its ecological niche. The environmental conditions under which a species can survive and reproduce is the fundamental niche. The fundamental niche (sometimes referred to as the physiological niche) provides a description of the set of environmental conditions under which a species can persist. However, a population's response to the environment may be modified by interactions with other species. Interactions such as competition may restrict the environment in which a species can persist. The portion of the fundamental niche that a species actually exploits as a result of interactions with other species is known as the realized niche. Species interactions can function to either restrict or expand the fundamental niche of a species dependent on whether the interaction is detrimental or beneficial.
To account for patchiness, ecologists often refer to:
Ecological density, which is the number of individuals per unit of living space.
Exploitation vs. interference:
Exploitation - individuals do not directly interact with one another. Interference - individuals interact directly wit one another, preventing others from occupying a habitat or accessing resources within it.
Small populations - because of their greater vulnerability to demographic and environmental Stochasticity and loss of genetic variability - are more susceptible to extinction than larger populations.
Extreme environmental events, such as droughts, floods, or extreme temperatures, can increase mortality rates and reduce population size. Severe shortages of resources can also cause possible extinction.
Describe density independent population regulation and provide examples:
Factors such as temperature, precipitation, and natural disasters (fire, flood, drought) may influence the rates of birth and death within a population but do not regulate population growth because regulation implies feedback.
Extrinsic ecological factors:
Factors such as the physical environment and the presence of predators or competitors directly influence age-specific rates of mortality and survivorship.
Density-independent factors:
Factors that can influence rates of birth and death independently of population density. If some environmental factor such as adverse weather conditions affects the population regardless of the number of individuals.
Explain reproductive effort and the trade-off between fecundity and survival:
Fecundity is the number of offspring produced per unit of time (bx), but the energetic costs of reproduction include a wide variety of physiological and behavioral activities in addition to the energy and nutrient demands of the reproductive event. Together, the total energetic costs of reproduction per unit time are referred to as an individual's reproductive effort. There is an inverse relationship between the number of offspring their probability of survival. As reproductive effort increased, the number of offspring increases, but probability of offspring survival decreases. As reproductive effort increases, parental survival decreases.
Acquisition of a mate involves sexual selection:
For females, the production and care of offspring represents the largest component of reproduction expenditure. For males, however, acquisition of a mate is often the major energetic expenditure that influences fitness.
Organisms may be unitary or modular:
Form, development, growth, and longevity of unitary organisms are predictable and determinate from conception on. The zygote, formed through sexual reproduction, grows into a genetically unique organism. There is no question about recognizing an individual. In modular organisms however, the zygote develops into a unit of construction, a module, which then produces further, similar modules. Most plants are modular in that they develop by branching, repeated units of structure.
The observed phenotypic variation within populations can arise from two sources:
Genotypic variation among individuals Interactions between the genotype and environment
When a defined area encompasses all of the individuals of a species, the distribution describes the population's ____.
Geographic range
Invasive species:
Humans are increasingly moving about the world. As they do so, they may either accidentally or intentionally introduce plants and animals to places where they have never occurred (outside of their geographic range). Although many species fail to survive in their new environments, others flourish. Freed from the constraints of their native competitors, predators, and parasites, they successfully establish themselves and spread.
What type of change in conditions might bring about the shift from semelparity to iteroparity?
If the external environment imposes a high adult mortality relative to juvenile mortality, and if individuals reach maturity, chances are that they will not survive much longer; therefore, future reproductive expectations are bleak. under these conditions, semelparity would be favored. If the opposite holds true and juvenile mortality is high compared to adult mortality, an individual has good chance of surviving into future once it survives to maturity., hence, prospects of future reproduction are good and iteroparity is favored.
The 4 processes that control population growth:
Immigration Birth rate Emigration Death rate
Mating systems describe the pairing of males and females:
In all sexually reproducing species, there is a social framework involving the selection of mates. The pattern of mating between males and females in a population is called the mating system.
Reproduction may be sexual or asexual:
In sexual reproduction between two diploid individuals, the individuals produce haploid (one half the normal number of chromosomes) gametes - egg and sperm - that combine to form a diploid cell, or zygote, that has a complement of chromosomes. Asexual reproduction produces offspring without the involvement of egg and sperm. It takes many forms, but in all cases, the new individuals are genetically the same as the parent.
Describe the trade-off between number and size of offspring:
In theory, a given allocation to reproduction can potentially produce many small offspring or fewer large ones. How a given investment in reproduction is allocated, the number and size of offspring produced, and the care and defense provided all interact in the context of the environment to determine the return to the individual in terms of increased fitness. The life history characteristics exhibit reaction norms as a result of interaction of environment and genotypes.
Individuals of a population may be distributed randomly, uniformly, or in clumps:
Individuals may be distributed randomly if each individual's position is independent of those of others. Individuals distributed uniformly are more or less evenly spaced. A uniform distribution usually results from some form of negative interaction among individuals, such as competition, which functions to maintain some minimum distance among members of the population. Uniform individuals defend an area for their own exclusive use. The most common spatial distribution is clumped, in which individuals occur in groups. Clumping results from social groups, clumped resources, suitable habitat, and many other factors.
A relationship that affects the population of two or more species adversely (--) is:
Interspecific competition. Like intraspecific competition, interspecific can be exploitation or interference.
Organisms that produce offspring more than once over their lifetime are called:
Iteroparous.
Parasatoidism:
Kills the host eventually. Lay eggs in or on the body of the host.
Early reproduction means earlier maturity, less growth, reduced fecundity per reproductive period, reduced survivorship and reduced future reproduction.
Later reproduction means increased growth, later maturity, and increased survivorship, but less time for reproduction.
Explain the structure of mating systems in animals:
Monogamy - involves the formation of a lasting pair bond between one male and one female. Monogamy exists mostly among species in which cooperation by both parents is needed to raise the young successfully. Instead of seeking other mates, the male can increase his fitness by continuing his investment in the young. Polygamy - the acquisition of two or more mates by one individual. It can involve one male and several females or one female and several males. A pair bonds exists between the individual and each mate. The individual having multiple mates (male or female) is typically not involved in caring for the young. Freed from parental duty, the individual can devote more time and energy to competition for more mates and resources. Polygeny - one male pairs with multiple females Polyandry - one female pairs with multiple males Promiscuity - males and females mate with one or many of the opposite sex and form no pair bond.
Growth of a population (population dynamics) is a function off age specific patterns of:
Mortality (survivorship) Fecundity (birthrate)
Discuss diffuse interactions:
Most interactions are not exclusive nor involve only two species... Rather, they involve a number of species that form diffuse associations. As a result, there is a potential for competition to occur among any number of species. The process in which a network of species undergoes reciprocal evolutionary change through natural selection is referred to as diffuse coevolution. The generalized relationship between groups of species - diffuse relationships between competitors, predator and prey, or mutualists.
An individual's life history represents the interaction between genotype and the environment:
Natural selection acts on phenotypic variation among individuals within the population and variation in life history characteristics, such as age maturity, allocation to reproduction, and the average number and size of offspring produced, is common among individuals within a population.
Preemptive competition:
Occurs primarily among sessile organisms, such as barnacles, in which occupation by one organism precludes establishment (occupation) by others.
Competition:
Occurs when individuals use a common resource that is in short supply relative to the number seeking it. Competition among individuals of the same species is referred to as intraspecific competition.
Parasitism:
One organism feeds on the other but rarely kills it outright, The parasite and host live together for some time. The host typically survives, although its fitness is reduced.
Describe the trade-offs in life history related to reproduction:
Organisms face trade-offs in life history characteristics related to reproduction. These trade-offs involve modes of reproduction, age of reproduction, allocation to reproduction, number and size of eggs, young, or seeds reproduced, and timing of reproduction. These trade-offs are imposed by constraints of physiology, energetics, and the prevailing physical and biotic environment - the organism's habitat. As such, the evolution of an organism's life history reflects the interaction between intrinsic and extrinsic factors.
Some organisms expend less energy during incubation. The young are born or hatched in a helpless condition and require considerable parental care. These animals are altricial.
Other animals have longer incubation or gestation, so the young are born in an advanced stage of development. They are able to move about and forage for themselves shortly after birth. Such young are called precocial.
The primary mating systems in plants are:
Outcrossing (cross-fertilization) - in which pollen from one individual fertilizes the ovum of another. Autogamy (self-fertilization) However, a mixed mating system, in which plants use both outcrossing and autogamy is common as well.
If a parent produces a large number of young, it can afford only minimal investment in each one. By dividing energy for reproduction among as many young as possible, these parents increase the chances that some young will successfully settle and reproduce in the future.
Parents that produce few young are able to expand more energy on each. The amount of energy varies with the number, size, and maturity of individuals at birth.
Populations have unique features because they are an aggregate of individuals. Populations have structure, which relates to characteristics of the collective, such as density, proportion of individuals in various age classes, and spacing of individuals relative to each other.
Populations also exhibit dynamics - a pattern of continuous change through time that results from the birth, death, and movement of individuals.
Populations can be divided into 3 ecologically important age classes or stages:
Pre-reproductive Reproductive Post-reproductive
Population growth:
Refers to how the number of individuals in a population increases or decreases over time. This growth is controlled by the rate at which new individuals are added to the population through the processes of birth and immigration and the rate at which individuals leave the population through the processes of death and emigration.
Intrinsic factors:
Relate to phylogeny (the evolutionary history of the species), patterns of development, genetics, and physiology - impose constraints resulting in trade offs among traits.
Sex ratios:
Sexually reproducing populations have a sex ratio that tends to be 1:1 at conception and birth but often shifts as a function of sex-related differences in mortality.
Social behavior may function to limit populations:
Social behavior appears to be a mechanism that limits the number of animals living in a particular habitat, having access to a common food supply, and engaging in reproductive activities.
Identify how social dominance, territoriality, and space pre-emption may regulate population size:
Social dominance plays a role in population regulation when it affects reproduction and survival in a density dependent manner. Territoriality can function to regulate population growth; the area that an animal normally uses during a year is its home range. By defending a territory, the individual secures sole access to an area of habitat and the resources it contains. Increased population density results in increased competition and smaller territory size for males that were successful in acquiring a territory. Plants can capture and hold onto space - plants occupy a certain amount of space and exclude individuals of their own and other species. Plants also establish zones of resource depletion associated with their canopy (leaves) and root systems.
Explain how coevolution influences species interactions:
Species interactions can function as agents of natural selection. The process in which two species undergo reciprocal evolutionary change through natural selection is called coevolution. Unlike adaptation to the physical environment, adaptation in response to the interaction with another species can produce reciprocal evolutionary responses that either thwart (counter) these adaptive changes, or in mutually beneficial interactions, magnify (reinforce) their effect.
Carrying capacity (K):
The carrying capacity is the maximum sustainable population size for the prevailing environment. The concept of carrying capacity suggests a negative feedback between population increase and resources available in the environment. As population density increases, the per capita availability of resources declines.
Explain a cohort life table and calculate survivorship:
The construction of a life table begins with a cohort, which is a group of individuals born in the same period of time. The first column of numbers, labeled x, represents the age of classes; the age classes are in units of years. The second column, n sub x, represents the number of individuals from the original cohorts that are alive at the specified age (x). When constructing life tables, it is common practice to express the number of individuals surviving to any given age as a proportion of the original cohort size (nx/n0). This value (lx) is referred to as survivorship and represents the probability at birth of surviving to any given age (x).
Distribution:
The distribution of a population describes its spatial location, or the area over which it occurs. The distribution of a population is influenced by the occurrence of suitable environmental conditions. Within the geographic range of a population, individuals are not distributed equally throughout the area. Therefore, the distribution of individuals within the population can be described as a range of different spatial scales. Individuals within a population are distributed in space. If the spacing of each individual is independent of the others, then the individuals are randomly distributed. If they are evenly distributed with a similar distance between individuals, there is uniform distribution. In most classes, individuals are grouped together or aggregated.
Distribution:
The distribution of a population describes its spatial location, the area over which it occurs. Distribution is based on the presence and absence of individuals.
Explain a fecundity table and calculate R sub 0:
The fecundity table uses the survivorship column, lx, from the life table together with the age specific birth rates (bx). Although bx may initially increase with age, survivorship (lx) in each age class declines. To adjust for mortality, we multiply the bx values by the corresponding lx (survivorship values). The resulting lxbx is the mean number of females born in each age group, adjusted for survivorship. The values of lxbx are summed over all ages at which reproduction occurs. The result represents the net reproductive rate, R0, defined as the average number of females that are produced during a lifetime by a newborn female. If the R0 value is 1, the females will replace themselves, if it is less than 1, the females do not replace themselves, and if the value is greater than 1, the females are reproducing more than enough females to replace themselves. The net reproductive rate (R0) therefore provides a means of evaluating both the individual (fitness) and the population consequences of specific life history characteristics.
The exponential model of population growth (dN/dt = b-dN) is based on several assumptions about the environment in which the population is growing...
The model assumes that essential resources (space, food, etc.) are unlimited and that the environment is constant, but this is not the case because the environment is not constant are resources are limited. As the density of a population increases, the demand for resources increases.
Explain the exponential model of population growth:
The model of exponential growth (dN/dt = rN) predicts the rate of population change over time. As with the pattern of geometric population growth, exponential growth results in a continuously accelerating (or decelerating) rate of population growth as a function of population size. Exponential growth is characteristic of populations inhabiting favorable environments at low population densities, such as during the process of colonization and establishment in new environments.
To study the population of modular organisms, we must recognize the two levels of population structure:
The module (ramet) and the individual (genet).
Distinguish between dispersal and migration:
The movement of individuals directly influences their local density. The movement of individuals in space is called dispersal, although the term dispersal most often refers to the more specific movement of individuals away from one another. When individuals move out of a subpopulation, it is referred to as emigration. When an individual moves from another location into a subpopulation, it is called immigration. Unlike the one-way movement of animals in the processes of emigration and immigration, migration is a round trip. The repeated return trips may be daily or seasonal.
Population density:
The number of individuals per unit area. Density measured simply as the number of individuals per unit area is referred to as crude density.
Population age structure:
The number or proportion of individuals in different age classes. Because reproduction is restricted to certain age classes and mortality is most prominent in others, the relative proportions of each age group bear on how quickly or slowly populations grow.
Age, stage, and size structure:
The number or proportion of individuals within each age class defines the age structure of population. Individuals making up the population are often divided into three ecological periods: pre-productive, reproductive, and post-reproductive. Populations can also be characterized by the number of individuals in defined classes of size or stage of development.
Genets vs. Ramets
The plant produced by sexual reproduction, thus arising from a zygote, is a genetic individual or genet. Modules produced asexually by the genet are ramets. These ramets are clones - genetically identical modules - and are collectively referred to as a clonal colony. Ramets may remain physically linked or separate.
Predation:
The process of one organism feeding on another, typically killing the prey.
Self-thinning:
The progressive decline in density and increase in biomass (growth) if the remaining individuals caused by the combined effects of density-dependent mortality and growth within a population.
Stochastic processes can influence population dynamics:
The stochastic (or random) variations in birthrates and death rates occurring in populations from year to year are called demographic Stochasticity, and they cause populations to deviate from the predictions of population growth based on the deterministic models. Besides demographic Stochasticity, random variations in the environment, such as annual variations in climate or the occurrence of natural disasters can directly influence birthrates and death rates within the population. Such variation is referred to as environmental Stochasticity.
Describe components of life history associated with r and K selected species:
The theory if r and K selection predicts that species adapted to these two different environments will differ in life history traits such as size, fecundity, age at first reproduction, number of reproductive events during a lifetime, and total life span.
We refer to populations in which immigration and emigration occurs as open populations.
Those in which movement into and out of the population does not occur (or is not a significant influence on population growth) are referred to as closed populations.
Provide examples of how species interactions can influence population dynamics:
Through their beneficial or detrimental effects on the individuals involved, these interactions influence the collective properties of birth and death at the population level, and in doing so, influence the dynamics of the respective populations. For example, as the number of predators in an area increases, the number of prey decrease. We would expect the predator population to increase as the size of the prey population increases.
Whether living independently or physically linked to the original individual, all ramets are part of the same genetic individual
Thus, by producing ramets, the genet can cover a relatively large area and considerably extend its life.
Identify the two processes of sexual selection and how these processes account for differences between sexes:
To explain why males and females of the same species often differ greatly in body size, ornamentation, and color (referred to as sexual dimorphism), Darwin developed a theory of sexual selection: Intrasexual selection - involves male to male (or sometimes female to female) competition for the opportunity to mate. It leads to exaggerated secondary sexual characteristics that aid in competition for access to mates, such as large size, aggressiveness, and organs of threat - like horns. Intersexual selection - involves the differential attractiveness of individuals of one sex to another. The female selects the male based on specific phenotypic characteristics. The result is increased relative fitness for those males that are chose, shifting the distribution of male phenotypes in favor of the characteristics on which female choice is based (such as bright coloration, elaborate plumage, vocalizations, etc.).
Life tables provide a schedule of age-specific mortality and survivorship:
To obtain a clear and systematic picture of mortality and survivorship within a population, ecologists use an approach involving the construction of life tables. The life table is simply an age-specific account of mortality. Population ecologists use life tables to examine systematic patterns of mortality and survivorship within animal and plant populations.
Different types of life tables reflect different approaches to defining cohorts and age structure:
Two basic kinds of life tables: (1) Cohort or dynamic life table - the fate of a group of individuals, born at a given time, is followed from birth to death. A modification of the dynamic life table is the dynamic composite life table - this approach constructs a cohort from individuals born over several time periods instead of just one. (2) The second type of life table is the time-specific life table - this approach does not involve following a single or group of cohorts, but is rather constructed by sampling the population in some manner to obtain a distribution of age classes during a single period of time. Although this is much easier to construct, it requires some crucial assumptions. First, it must be assumed that each age class was sampled in proportion to its numbers in the population. Second, it must be assumed that the age-specific mortality rates (and birthrates) have remained constant over time.
r-selected species:
Typically short-lived High reproductive rates at low population densities Rapid development Small body size Large number offspring with low survival Minimal parental care Unstable environments
The difference between the number of individuals alive for any age class (nx) and the next older age class (nx + 1) is the number of individuals that have died during that time interval.
We define this value as dx, which gives us a measure of age-specific mortality. The number of individuals that died during any given time interval (dx), divided by the number of alive at the beginning of that interval (nx), provides an age-specific mortality rate, qx.
A variety of factors can lead to population extinction:
When deaths exceed births, populations decline. R0 becomes less than 1.0 and r becomes negative. Unless the population reverses the trend, it may become so low that it declines toward extinction.
Classify species interactions based on their reciprocal effects:
When neither of the two populations affects the other, the relationship is neutral (00). If the two populations mutually benefit, the interaction is (++) or positive and known as mutualism. When one species maintains or provides a condition that is necessary for the welfare of another but does not affect its own well-being, the relationship (+0) is called commensalism. When the relationship is harmful to both species (--) the interaction is termed competition. When one species reduces or harms the population of another, but the affected species has no influence in return (-0) the relationship is amensalism. Predation, parasitism, parasatoidism, are (+-) and one species benefits at the expense of the other.
Differentiate between scramble and contest competition:
When resources are limited, a population may exhibit one of two responses: scramble competition or contest competition. Scramble competition occurs when growth and reproduction are depressed equally across individuals in a population as the intensity of competition increases. At extremes, scramble competition can lead to all individuals receiving insufficient resources for survival and reproduction - resulting in local extinction. Contest competition takes place when some individuals claim enough resources while denying others a share. Only a fraction of the population suffers - the unsuccessful individuals.
Abundance:
Whereas distribution defines the spatial extent of a population, abundance defines size - the number of individuals in the population. The population abundance is the total number of individuals in a defined region. Abundance is a function of two factors: (1) population density and (2) the area over which the population is distributed.
We can rewrite the equation for population growth that includes the rates of birth and death that vary with population size using the value of carrying capacity, K.
dN/dt = rN(1 - N/K) In this form, known as the logistic model of population growth, the per capita growth rate, r, is defined as b0 - d0. As the population grows and N approaches K, population growth slows down. If the population density exceeds K, population growth becomes negative.
