Biology 205Biology 205Ecology and AdaptationEcology and Adaptation

Exam 3: Exam 3: ReviewReview

Fall 2015Fall 2015Dr. Erik D. DavenportDr. Erik D. Davenport

• Principle of AllocationPrinciple of Allocation: Only certain amount of energy is available to a living organism. If organisms use energy for one function such as growth, the amount of energy available for other functions is reduced.

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Main concept 1:Offspring Number Versus Size

Because all organisms have access to limitedlimited energy and other resources, there is a trade-off between the number and size of offspring;

those that produce larger offspring are those that produce larger offspring are constrained to produce fewer; while those constrained to produce fewer; while those

that produce smaller offspring may produce that produce smaller offspring may produce larger numberslarger numbers.

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Egg Size and Number in Fish• Fish show more variation in life-history than any

other group of animals.• Darter fishDarter fish as an example….

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Main concept 2:

Adult survival rate vs. reproduction ageWhen adult survival is lower, organisms begin

reproducing at an younger age and invest a greater proportion of their energy budget into reproduction;

where adult survival is higher, organism defer reproduction to a later age and allocate a smaller proportion of their resources to reproduction.

What will be the results on individual body size?

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Concept 3: Life History Classification

• MacArthur and Wilson– r selectionr selection (per capita rate of increase)

• Characteristic high population growth rate.– K selectionK selection (carrying capacity)

• Characteristic efficient resource use.• Pianka : r and K are ends of a spectrum, while most

organisms are in-between.– r selection: Unpredictable environments.– K selection: Predictable environments.

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r and K: Fundamental Contrasts

Per captia Rate of Increase:– Highest in r selected species.

Competitive Ability:– Highest in K selected species.

Reproduction:– r: Numerous individuals rapidly produced.– K: Fewer larger individuals slowly produced.

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IMPORTANT!!!!

Modes of Competition

• InterferenceInterference: – Direct aggressive interaction between individuals.

• IntraspecificIntraspecific: – Competition with members of own species.

• InterspecificInterspecific: – Competition between individuals of two species -

reduces fitness of both.

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Intraspecific Competition Among Herbaceous Plants

• Plant growth rates and weights have been found to increase in low density populations.

• Competition for resources is more intense at higher population densities.

• Usually leads to mortality among competing plants.• Self-Thinning: As the population of the trees Self-Thinning: As the population of the trees

develops, more and more biomass is composed of develops, more and more biomass is composed of fewer and fewer individuals, this process is called fewer and fewer individuals, this process is called self-thinning. Why??????self-thinning. Why??????

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• Self-thinningSelf-thinning appears to result from intraspecific competition for limited resources, as a local population of plants develops, individual plants take up increasing quantities of nutrients, water, and space for which some individuals compete more successfully, the loser in this competition for resources die, and population density decrease as a consequence. Over time, the population is composed of fewer and fewer large individuals.

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What model is used for the intraspecific competition??

dN/dt = rN(1-N/K)dN/dt = rN(1-N/K)

• r = per capita rate of increase under ideal conditions.

• Logistic population growth model.• What term in this model describe the intraspecific

competition???

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Lotka Volterra

Effect of interspecific competition on population growth of each species:

– dNdN11 / d / dtt = r = rm1m1NN11 ((K ((K11-N-N11- - αα 1212NN22) / K) / K11))– dNdN22 / d / dt t = r= rm2m2NN22 ((K ((K22-N-N22- - αα 2121NN11) / K) / K22))

α12: Effect of individual of species 2 on rate of pop. growth of species 1.

α21: Effect of individual of species 1 on rate of pop. growth of species 2.13

Lotka-Volterra

The Lotka-Volterra model incorporates interspecific competition by using a parameter called α.

α is the coefficient of competition (or competition coefficient) and measures the competitive effect of one species on another. (IMPORTANT!!!!)

For example: α12 is the effect of species 2 on species 1, α21 is the effect of species 1 on species 2.

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Predicting the outcome of competition

The outcome of competition, according to the Lotka-Volterra model, is ultimately determined by

carrying capacity (Ki) and the competition coefficient (aij) of the two

species

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examples

Green sunfish Bluegill K1 = 600 K2 = 600 r1 = 0.10 r2 = 0.10 α12 = 1.50 α21 = 0.90

What is the results of this completion?

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Introduction

• ExploitationExploitation: Interaction between populations that enhances fitness of one individual while reducing fitness of the exploited individual.– PredatorsPredators kill and consume other organisms.– ParasitesParasites live on host tissue and reduce host

fitness, but do not generally kill the host.– PathogensPathogens induce disease.

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Population Cycles in Mathematical and Laboratory Models

• Lotka Volterra assumes host population grows exponentially, and population size is limited by parasites, pathogens, and predators:

dNdNhh/d/dtt = r = rhhNNhh – pN – pNhhNNpp

• rhNh = Exponential growth by host population.– Opposed by:

• P = rate of parasitism / predation.• Nh = Number of hosts.• Np = Number of parasites / predators.

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Population Cycles in Mathematical and Laboratory Models

• Lotka Volterra assumes parasite/predator growth rate is determined by rate of conversion of food into offspring minus mortality rate of its own population:

dNdNpp/d/dtt = cpN = cpNhhNNpp-d-dppNNpp

• cpNhNp = Conversion rate of hosts into offspring.• pNhNp = Rate at which exploiters destroy hosts.• c = Conversion factor

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Predator vs. Prey

Without predator, Prey population will grow exponentially.

Without prey, predator population will decrease (die)

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Model Behavior

Host exponential growth often opposed by exploitation.– Host reproduction immediately translated into

destruction by predator.– Increased predation = more predators.– More predators = higher exploitation rate.– Larger predator population eventually reduces host

population, in turn reducing predator population.

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Model Behavior

Reciprocal effects produce oscillations in two populations.

Although the assumptions of eternal oscillations and that neither host nor exploiter populations are subject to carrying capacities are unrealistic, L-V models made valuable contributions to the field.

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Refuges

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Introduction

Mutualism: Interactions between individuals of different species that benefit both partners.

– Facultative Mutualism occurs when a species can live without its mutualistic partner.

– Obligate Mutualism occurs when a species is dependent on a mutualistic relationship.

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Introduction

Community: Association of interacting species (population) inhabiting some defined area.

Community Structure includes attributes such as number of species, relative species abundance, and species diversity.

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Pattern of Species Abundance

There are regularities in the relative abundance of species in communities that hold irregardless of the ecosystem.

Most species are moderately abundant; few are very abundant, or extremely rare.

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Environmental Complexity

In general, species diversity increases with environmental complexity or heterogeneity. why???

– Higher environmental complexity will introduce a more diversified environments -- more niches

– More niches higher species diversity

Many studies have shown positive relationship between environmental complexity and species diversity.

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Environmental Complexity

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Disturbance and Diversity

Disturbance difficult to define as it involves departure from “average conditions.”– Average conditions may involve substantial

variation. Sousa defined disturbance:

– Discrete, punctuated, killing, displacement, or damaging of one or more individuals that directly or indirectly creates an opportunity for new individuals to be established.

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Disturbance and Diversity

White and Pickett defined disturbance:– Any relatively discrete event in time that disrupts

ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment.

– Two major characteristics: Frequency Intensity

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Intermediate Disturbance Hypothesis

Connell proposed disturbance is a prevalent feature that significantly influences community diversity.– Proposed both high and low levels of disturbance

would reduce diversity.– Intermediate levels promote higher diversity.– Sufficient time between disturbances allows wide

variety of species to colonize, but not long enough to allow competitive exclusion.

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Disturbance and Diversity in the Intertidal Zone

Species interactions and community structure

• The most important interactions in a community are:

• Feeding relationships provide some of the most easily documented examples of interactions within community.

• Food webFood web: a summary of the most the feeding interactions within a community, is one of the most basic and revealing descriptions of a community structure.

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Community Webs

• AA food webfood web summarizes the feeding relationship summarizes the feeding relationship in a communityin a community..

• Summerhayes and Elton studied feeding relations on Bear Island in High Arctic.– Primary producers were terrestrial plants and aquatic

algae.– Fed on by several kinds of terrestrial and aquatic

invertebrates.– Consumed by birds.– Attacked by arctic foxes.

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Arctic Food Web

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Food Web Complexity

The level of food web complexity increases dramatically with more diverse communities.

Winemiller described feeding relations among tropical freshwater fish.

Represented food webs in various ways:– Only included common species.– Top-predator sink.– Excluded weakest trophic links.

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Strong Interactions and Food Web Structure

• Paine suggested feeding activities of a few species may have a dominant influence on community structure. He called these important trophic relations strong interactions.strong interactions.

• Suggested criterion for strong interaction is based on the degree of influence on community structure.

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Keystone Species

• Keystone speciesKeystone species: the species has the most significant influence on community structure.

• The feeing activities of few keystone species may control the structure of communities.

• If keystone species reduce likelihood of competitive exclusion, their activities would increase the number of species that could coexist in communities.( some predator may increase species diversity).

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Exotic Predators

Exotic predator can collapse and simplify the structure of food web.

Exotic species have dramatic impacts on communities because they were outside the evolutionary experience of local prey populations.– Nile Perch (Lates nilotica) exotic fish predator in

Lake Victoria.– Fish fauna dramatically reduced.

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