Ecology Study Guide Exam 2 PDF

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Ecology Exam 2

Lecture 8 — Intraspecific Competition: • Interspecific Competition: Competition between members of DIFFERENT species.

• Intraspecific Competition: Competition between members of the SAME species. Causes one of two responses — Scramble Competition or Contest Competition. Usually only one type occurs w/in a specific species. Both can occur at different moments pending situation.

• Scramble Competition: Resources depleted to the point that no individual survives. Growth and reproduction are depressed equally over individuals in a population as intensity of competition increases; entire pop. gets insufficient amount of resources leading to extinction.

• Contest Competition: When a limited resource is shared only by dominant individuals; a relatively constant number of individuals survive, regardless of initial density.

• Exploitative Competition: Competition by a group or groups of organisms that reduces a resource to a point that adversely affects other organisms.

• Interference Competition: Competition in which access to a resource is limited by the presence of a competitor. !

• Population Growth Rate: Change in number of individuals in a population over time. General equation that you can use to get more specific forms of the equation. • Population Growth Rate Equation: Assumes no movement of individuals into or out of the population therefore giving us r as a function of birth and death rates. ! ! ! ! ! ! ! dN/dT = Growth Rate of Pop. at an Instant ! r = Per Capita Rate of Increase ! ! (How quickly the population grows per individual already in the population) ! N = Population Size ! T = Time of Growth !

• When the per capita rate of increase (r) takes the same positive value regardless of the population size, then we get exponential growth. !

• When the per capita rate of increase (r) decreases as the population increases towards a maximum limit, then we get a logistic growth. ! ! ! !1

Ecology Exam 2 ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

• Exponential Population Growth: Instantaneous rate of population growth, expressed as proportional increase per unit of time. **Growth rate remains the same regardless of population size, making the population grow faster and faster as it gets larger. (JCurve;Bacteria) • Maximum per Capita Rate of Increase (rmax ) Biotic Potential: Max rate at ideal conditions for particular species (depends on unattainable infinite amount of resources)!

• Creates Positive Feedback: Instantaneous growth rate which increases as pop density increases. (Autocatalytic) BUT natural pop cannot exist without bounds. !

• Exponential Population Growth Equations:! ! !

Nt = N0 e rt

Nt = Pop. Density at Time (t)! N0 = Initial Pop. Density r = Intrinsic Growth Rate t = Time Since Initial Population! dN/dT = Growth Rate of Pop r = Per Capita Rate Increase N = Population Size T = Time of Growth rmax = Max per Capita Rate !2

Ecology Exam 2

• Logistic Population Growth: Population growth curve in which rate of increase decreases linearly as population size increases.! ! **Growth rate gets smaller and smaller as population size approaches a maximum imposed by limited resources in the environment AKA carrying capacity (K). (S-Curve;Yeast)! ! **Relationship between the rate of population growth (Nt) and population size (N) takes the form of a parabola, reaching its maximum value at a population size of N = K/2. ! ! **Have to assume the population has a base growth rate of rmax when it is very small. !

• K - N = tells us how many more individuals can be added to the population before it hits carrying capacity. !

• (K - N) / K = tells us the fraction of the carrying capacity that has not yet been “used up”. The more carrying capacity that has been “used up”, the more (K - N) / K will reduce the growth rate. !

• When the population is very tiny, N = very small compared to K thus the (K - N) / K becomes approx. (K / K) = 1 which gives us back the exponential equation. Fits with the graph showing high increased rate of exponential growth initially then the rate levels off as it approaches the carrying capacity K. !

• Logistic Population Growth Equation: ! !

Nt = r N [1 - (N/K)] !

Nt = Population Density at Time (t)! N = Initial Population Density r = Intrinsic Growth Rate K = Carrying Capacity! dN/dT = Growth Rate of Population rmax = Max per Capita Rate Increase !

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• So the question is… What regulates population growth?? ! • A Negative Feedback System created from the population density’s own effect on the population growth, reproduction and survivorship.

• Density dependence: Effects that influence a population in proportion to its density. • This negative feedback system creates a negative density dependence which is implicit in the carrying capacity concept of the logistics growth model. !3

Ecology Exam 2

• Carrying Capacity (K): Number of individual organisms that the resources of a given area can support, usually through the most unfavorable part of the year. Max sustainable population size for the prevailing environment as a function of supply of resources. ! !

( b0 - d0 ) ! K= ! (a+c) ! ! ! ! ! ! ! ! !

K = Carrying Capacity b0 = Maximum Birth Rate d0 = Maximum Death Rate a = Slope of Birth Rate Relative to Pop Size c = Slope of Death Rate Relative to Pop Size

• Determined by factors/resources important to the species which can reduce the species’s population in any way acting as a limit. !

• Limited key resources leads to INTRA-specific competition. ! • Comparison of Graphs: ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

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Ecology Exam 2

• Projecting Future Population Size: Predicting behavior of the population using the following equation. ! ! ! ! ! ! ! ! !

• Logistic Model Assumptions When Projecting Future Population Size: (In addition to the assumptions for exponential growth)!

• Constant Carrying Capacity: • Resource availability does not change through time. • Or they change predictably according to stochastic / random events; periodic •

variation / seasonal changes; refuge / ability to avoid predation (can eventually spot a trend and apply to data and we understand the reasoning behind these trends) Linear Density Dependence: • With regard to the per capita growth rate. Max growth rate occurs when N = 0. Increasing density = ALWAYS detrimental • But reduction in reproduction or survival under low population densities, namely the Allee effect, is detrimental as well. Density Dependence operates equally on all components of r. !

• • • ! ! ! ! ! ! ! ! ! ! ! ! !

• Intrinsic Growth Rate (r): [(Birth + Immigration) - (Death + Emigration)]

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Ecology Exam 2

• Density Dependence: Regulation of population growth by mechanisms controlled by the size of the population; effect increases as population size increases. !

• Effects which influence the population in proportion/relation to its size. ! • Function to slow down the rate of population growth with increasing population density by increasing the rate of mortality (known as density-dependent mortality), decreasing rate of birth (density-dependent fecundity) or both methods. !

• Mechanisms of Density Dependence Population Regulation: • Mechanistic Models: represent the underlying processes directly, with functions and distributions that are based on theoretical reasoning about ecological processes of interest. !

• May include factors which are not related to the direct effects of resource availability • Ex. population density can influence patterns of predation or the spread of disease/parasites. !

• May include factors which are directly influence the rate of birth/death function independently or population density. • Ex. adverse weather conditions which affect population regardless of how many individuals are present. (see density independent) !

• Discuss mechanisms for intraspecific competition: • Density-Dependent Fecundity: Decline in fecundity (birth) rate with increasing population size. !

• Density-Dependent Growth: Inverse relationship between population density and individual growth. !

• Density-Dependent Mortality: Increase in mortality (death) rate with increasing population size. !

• Inverse Density-Dependence in Small Populations: Allee effect which is a densitydependent mechanism identified to function to reduce rates of birth and survival at low population densities as a population regulation method. !

• Small pop can be susceptible to a variety of factors which directly influence survival and birth rates resulting from life history characteristics related to mating, reproduction and defense. Results in an inverse density dependence where at low pop size birthrate declines or mortality increases; and below some minimum population density, the rate of population growth is negative.

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Ecology Exam 2

• Example: Large cats that are widely dispersed having trouble finding a mate when pop is scarce. Pop density falls, decreases probability of reproduction.!

• Density Independence: Being unaffected by population density; regulation of growth is not tied to population density. Direct influence of birth/death rates independent of population density such as environmental factors which affect the population no matter how many individuals there are in a population -OR- in the case that the proportion of individuals affected by the factor is the same at any density. !

• Pg 223 Figure 11.4 Graphs representing the effects influencing the population density…! !

• Factors such as temperature, precipitation, natural disasters which influence birth and death in a population but do not regulate the population growth as the term regulation of population growth implies the creating of a feedback system playing a role on the population. • If environmental conditions exceed an organism’s limits of tolerance, it can affect growth, maturation, reproduction, survival and movement resulting in increase mortality which can lead to extinction of local pop. • Large changes seen in pop growth due to Density-Independent factors come from variation in moisture content and temperature.

Learning Objectives: • Define competition • Competition: When individuals use a common resource that is in short supply relative to the number seeking it — resources being items used by population which can affect their population growth rate (nutrients, habitat/space, sunlight, mates). • As long as the availability of resources does not impede the ability of individuals to survive, grow and reproduce, no competition exists. !

• Once resources are insufficient to satisfy all individuals in the population, the means by which they are allocated has a marked influence on the welfare of the population. !

• Significance of competition — known to influence natural selection and regulate population densities.

• Distinguish between intraspecific and interspecific forms • INTRA = Within same Species sharing same resources/factors. • Intraspecific Competition Increases gradually, at first only affecting growth and development but later, it affects individual survival and reproduction.!

• INTER = Within a community of different species sharing same resources/factors. !

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Ecology Exam 2

• Explain how intraspecific competition can regulate populations - Explore the variety of interaction among individuals within a population that can influence the rates of birth and death and therefore the rates of density-dependent population growth.

• Use the logistics growth model to characterize the effects of intraspecific competition • Evidence that the density dependence operates on many different aspects of population growth: • Growth and development: As pop density causes decrease in resources, individuals reduce their intake of resources causing slowing of the rate of growth and development. • Inverse relationship between pop density and individual growth (densitydependent growth) • Example: Mean weight of individual plants planted in a pot together decreases with the increasing pop density of plants in the pot. !

• Mortality: As pop density increases, chance of survival decreases thus, mortality increases the availability of resources therefore allowing for increased growth of the surviving individuals. • Creates direct link between density-dependent mortality — resource availability — population growth rate. • Example: Seedlings and plants in competition in the wild. Less to compete with, more space and resources for the survivors to use. !

• Reproduction: Population density affects the rate of which some species mature and reach reproductive viability, thus density dependence takes a toll on the rate of maturity as well as the amount of eggs produced within a larger population as opposed to a smaller population. • Direct result of the inverse relationship between the individual growth rates and population density. • Example: Harp seals and fish grow less in higher populations, reaching reproductive maturity later than usual and thus decreasing the rate of reproduction in the population. Tons of plants produce less seeds in higher population densities. !

• Stress: Increased crowding and forced social contact increases stress in the individual with trigger hormonal changes which can repress growth, curtail reproductive function, and delay sexual activity. • Example: Increased social stress in pregnant mammals sometimes increases mortality rate and cause inadequate ability nursing of the young stunting their growth and development. !

• Dispersal: As a reaction to stress of overpopulation, some animals disperse, leaving the population in search of vacant habitats. Most apparent when pop density is high !8

Ecology Exam 2 but occurs regularly. BUT more importantly dispersal applies when the population density is dwindling and individuals disperse as a reaction to low or increasing density, well before the pop reaches the point of overexploiting the resources which prevents extinction. • **Does not function as a population regulatory method but it does contribute strongly to population expansion and the persistence of local populations. !

• Social Behavior/Dominance: Degree at which individuals tolerate one another. Mechanism which limits the number of animals living in a particular habitat and having access to a common food supply, and engaging in reproductive activity. Sometimes form necessary group structure based on aggressiveness, intolerance, and dominance of one individual over another. • Plays role in pop reg when it affects reproduction and survival in a densitydependent manner. • Example: Wolves living in small packs with their alpha male/alpha female. Only alphas mate to prevent lower hierarchies from mixing with them. The reproducing pair of alphas are given precedence over the rest of the pack in terms of resources. At low densities every reproductive able female mates to increase the population. At high densities, only the alphas mate to add to population. !

• Territoriality (animals) / Space Capture (plants): Dominating certain areas creates only a floating reserve of those who mate to repopulate. Home range sizes in mammals are related to body size which reflects the link between body size and energy requirements. Generally carnivores require larger home range than herbivores and omnivores of the same body size; Males and adults have larger home range than females and juveniles. Plants take over space with their roots and by blocking sun getting to other plants. !

• Home Range: Area over which an animal ranges throughout the year. • Territory: Area defended by an animal; varies among animal species according to social behavior, social organization, and resource requirements. If animal defends whole home range, the entire home range is its territory.

• Territoriality: Functions to limit access to the defended area by other individuals in the population. • If all pairs settle in an area and are able to establish a territory, territoriality only establishes the spatial distribution of these individuals and does not regulate it. !

• When there is an excess of males an females of reproductive age unable to establish breeding territories, reproduction will become limited and !9

Ecology Exam 2 territoriality is then acting as a mechanism of density-dependent population regulation.

• Identify the four types of competition: Scramble VS Contest; Exploitative VS Interference • How do organisms access resources? ! • Scramble Competition: All individuals have access to the resources; able to consume as much as needed/possible. !

• Contest Competition: Individuals have all or none access to resources. ! !

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• How do organisms interact? ! • Exploitative Competition: No direct interaction; interaction is resource mediated. ! • Interference Competition: Direct interaction between individuals. ! ! ! !10

Ecology Exam 2 !

Intraspecific Competition

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How do organisms access resources?

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How do organisms interact?

Exploitative Interference Scramble

SE

SI

Contest

CE

CI

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• Summarize the modeling homework

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Ecology Exam 2

Lecture 9 — Interspecific Competition • Interspecific Competition: A relationship which affects the population of two or more species adversely (- , - ) where individuals are still seeking a common resource that is in short supply, but this time the competition occurs between the individuals of two or more species. • Takes two Forms Like Intraspecific Competition: • Exploitation and Interference. !

Possible Ways 2 Species Can Interact: !

Species 2 ! !

+ Beneficial +

0 Neutral 0

- Harmful -

+ Beneficial +

++ Mutualism

+0 Commensalism

+Predation

0 Neutral 0

0+ Commensalism

00 Neutralism

0Amensalism

- Harmful -

-+ Predation

-0 Amensalism

-Competition

Species 1

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• Competitive Exclusion Principle: Two species competing for the exact same resource cannot stably coexist if other ecological factors relevant to the organism remain constant. One of the two competitors will always outgrow the other leading to extinction of one of the competitors; complete competitors cannot coexist. !

• Resource Partitioning: Species which share the same habitat and have similar needs which frequently use resources in somewhat different manners thus, they don’t come into contact/ direct competition for at least part of the limiting resource. • Negates Competitive exclusion principle. • Could be evolutionary response to interspecific competition. !

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Ecology Exam 2

• Use Lotka-Volterra (LV) Model to describe and build understanding of BOTH intraspecific and interspecific competition: • Lotka-Volterra Competition Equations: Describes the relationship between two species using the same resource, like in consumption competition, which take into account intra, and interspecific competition. Captures the fact that species can compete for res...