Ecology Exam 2

Lectures 1 - 6 and Jeopardy questions

What are the three survivorship curves and examples of each?

• Type 1 (Convex):

  • More likely to die as you age. Humans

• Type 2 (Diagonal)

  • Consistent mortality. Birds

• Type 3:

  • High mortality at the start. Trees

What does logistic growth look like? What is an example of an organism exhibiting logistic growth, and what is K?

• K =  carrying capacity = the maximum number of individuals an area can support

• Increases as N → K; dN/dt approaches 0

• Eurasian collared doves in Britain, acorn barnacles, northern elephant seals

What is symbiosis? Name three kinds of symbiosis

• When multiple organisms live together intimately, most or all of the life cycle of one organism occurs in another

• Mutualism, commensalism, and parasitism

What does the equation represent? What does each variable mean?

Net reproductive rate for annual plants

• R₀ = Net reproductive rate (like the average number of seeds produced by an individual in a population during its lifetime)

• I₀ = Percent of the population surviving to each age

• m_x = Average number of seeds produced by each individual in each age category

• x = Age interval

What is Gause’s competitive exclusion principle? What does it predict, and what does it have to do with character displacement?

• Two species with identical niches cannot coexist indefinitely (leads to competitive exclusion) – Paramecia experiments

• Predicts that species living together have different niches (niche partitioning)

• Character displacement: Sympatric species have more dissimilar traits vs. allopatric

  • Six requirements:

    • Differences are genetic

    • Differences evolved when living together

    • Species are more different when together than when apart

    • Specific traits affect resource gathering/use

    • Similar traits lead to more competition

    • Traits are not caused by different locations

What are the three main methods of estimating patterns of survival? 

• Cohort life table: Identify individuals born at the same time and keep records from birth

• Static life table: Record the age at death of individuals

  • Age distribution: Calculate differences in the proportion of individuals in each age class

What is a rank-abundance curve? How can you tell richness and evenness from it?

A rank abundance curve is used to display and compare biodiversity, specifically species richness and species evenness, within a community.

• X-axis (Rank): Species are ranked from left to right in order of abundance, where Rank 1 is the most abundant species, Rank 2 is the second most abundant, and so on

• Y-axis (Relative Abundance): The vertical axis shows the relative abundance (proportion or percentage) of each species

• Richness: How many species there are

• Evenness: The relative abundance and proportional representation of each species within a biological community

  • Lower slope = species have similar/even abundances

  • Steep drop = One or few species dominate the environment

How does the Lotka-Volterra predator-prey model predict predators and prey will change through time? What does a plot of predators vs. prey look like?

• Predator and prey populations oscillate. Prey peak always slightly behind the predators.

  • Prey increase → predators increase → Prey decrease → Predators decrease

• If you eliminate the time axis, there is an elliptical oscillation in predator and prey numbers

  • It is called a phase plot

What is the equation for geometric growth, and in what cases would you use it?

• Geometric growth is a constant ratio that describes how a population multiplies during a discrete period of time

  • Generations do not overlap

  • Generations differ in size by a constant ratio

  • Lambda = 1 is no population growth

  • Example: Annual plant with abundant resources

What disturbance conditions generate the most diversity? Give an example

• Intermediate levels

• Intermediate disturbance hypothesis

• Algae and invertebrates

  • Diversity of algae and invertebrates growing on boulders in the intertidal zone

  • Boulders supporting the greatest diversity of species were those subject to intermediate levels of disturbance

What is the exponential growth rate equation, and when would you use it?

• Continuous population growth in an area where resources are not limiting

• Characteristic of rebounding populations (elephants) or establishing in a new environment/during newly favorable conditions (e.g., Scots pines, whooping cranes)

• dN/dt = rN

  • dN/dt = rate of population growth)

  • R = per capita rate of population increase (this is constant)

  • N = population size

What is the logistic growth rate equation, and when would you use it?

• Accounts for carrying capcity/limiting resources

• dN/dt = r_max N (1 - N/K)

  • Change in numbers / Change in time

  • Intrinsic rate of increase

  • As the ratio of population size to carrying capacity (N/K) approaches 1, the population growth rate approaches 0."

What are the different types of species interactions?

• Mutualism +/+

• Commensalism +/0

• Predation/Herbivory/Parasitism +/-

• Amensalism -/0

• Competition -/- 

What assumptions does the Lotka-Volterra predator-prey model make? What confounding variables might occur in reality?

• Assumes:

  • Prey population grows exponentially in absence of predators

  • Predator population declines exponentially without prey

  • Predators consume prey at rate proportional to prey density

  • No predator interference or competition

  • Environment is constant

  • No age structure or spatial structure

  • Predator and prey interact continuously

• Showed that predator-prey interactions could produce population cycles

What increases species diversity in a community? Give specific examples

• Environmental heterogeneity/complexity

• Examples:

  • MacArthur, birds, tree height diversity

  • Hutchinson’s Paradox of the plankton

  • Variation in soil type and depth to groundwater

What are the three types of competition? Give an example of each. What type of niche does competition affect?

• Interference competition: Direct interactions between individuals where organisms actively block, fight, or intimidate others to stop them from accessing a shared, limited resource (opposite of exploitative competition)

  • Aggressive territory defense, production of chemical toxins

• Intraspecific competition: Individuals of the same species

  • Self thinning

• Interspecific competition: Individuals of different species

  • Can affect species' realized niche

What are the three types of competition? Give an example of each. What type of niche does competition affect?

A metapopulation is a "population of populations"—a group of spatially separated populations of the same species that live in fragmented habitat patches.

Connection to dispersal: Dispersal allows individuals to move between habitat patches and recolonize empty ones after local extinctions, preventing the entire metapopulation from dying out.

What is an example of a density-independent and a density-dependent factor that limits population growth?

• Density-independent: Tend to be abiotic factors

  • Volcanic eruption

• Density-dependent: Tend to be biotic factors

  • Reproductive success of sparrows

What is the Lotka-Volterra competition model, and what does it predict about coexistence?

• Competition model that predicts coexistence when interspecific competition is weaker than intraspecific competition (related to Gause’s principle)

What are the two types of mutualism? What are examples of each?

• Facultative: Species can live independently

• Obligate: Depend on the relationship for survival

• Can be specialized or generalist–each plays a different role in mutualism networks (specialist pollinators often interact with generalists; loss of generalist can have big consequences)

What are types of refuges?

• Flight, Size, Space, Large groups, Fear

When does theory predict mutualism will occur? What factors contribute to this in the ant-plant system?

• Theory predicts that mutualism will evolve when benefits are larger than costs (for combined successful and unsuccessful mutualists)

• For ant plants

  • High probability of attracting ants

  • High potential for herbivory

  • Low effectiveness of alternative defences

  • High effective ant defenses

What is the difference between species richness and species diversity?

Species richness is simply the total count of different species in a community, while species diversity accounts for both the number of species (richness) and how evenly individuals are distributed among them (evenness).

How does nutrient enrichment influence species diversity?

• Nutrient enrichment reduces environmental complexity, which reduces diversity (plants and algae)

• Light becomes limiting, and the best light competitor dominates

Guild define & examples

A group of organisms that all make their living in a similar way

Ex: Seed-eating animals in the desert, fruit-eating birds in the tropics, filter-feeding invertebrates in tide pools

Life-form define

Life-form: Combination of structure and growth dynamics of plant (similar to guild)

What is the universal pattern of relative species abundance across different ecosystems?

Very few abundant species, very few rare species, most species are moderately abundant

Species richness define

Number of species in community

Species evenness define

Relative abundance of species

Compare/Contrast species richness and species evenness

What are possible reasons that communities could have the same species richness, but different species evenness?

1. Space requirements

2. One is more adapted with local spcies

3. Nutrient soil requirements

What is this equation?

Define the variables

Shannon Wiener Index: Measures evenness

H' = Value of SW diversity index

• Higher = More diversity

• H = 0 = One species/No diversity

P_i = Proportion of the ith species in sample

Log_ep_i = Natural log of p_i

s = Number of species in the community

What are the reasons that ecologists care about species diversity?

1. Ecosystem stability and resilience

2. Understanding ecosystem

3. Detecting environmental change

4. Comparing ecosystems scientifically

5. Conservation prioritization

What is this curve? What do the lines/slopes represent? What are the axises?

What does a low slope indicate on a rank-abundance curve?

What does a steep slope indicate on a rank-abundance curve?

Low slope indicates greater species evenness

Steep slope indicates less species evenness

What variavles play a role in differences in evenness shown in rank-abundance curves?

Niche differences

Neutral dynamics

Competition

Predation

Environmental Factors

Disturbance

True or False: Species diversity decreases with environmental complexity or heterogeneity

False: Species diversity increases with environmental complexity or heterogeneity

Why does species diversity increase with environmental complexity?

There are more niches & resources since it is more complex

Discuss an example of diversity increasing with environmental complexity

Bird/Warbler diversity increased as vegetation stature increased

Measured complexity in the form of foliage height

Forests with the greatest volume of folaige above 6m contained five or more warbler species

What is the paradox of the plankton

Phytoplankton communities live in simple environments all competing for the same nutrients, however many species coexist without competitive exclusion

• Coexistence is maintained by:

  • Environmental variability (Light, temperature, nutrients changing)

  • Predation: Preventing any one species from dominating

  • Spatial heterogeneity

  • Trade-offs among species: Growth rate vs. nutrient efficiency

Discuss the niches of algae

Algae niches are defined by their nutrient requirement

• Freshwater diatoms dependend on ratio of silicate:phosphate

• Diatoms vary in phosphorus uptake rate

• Variation in availability of limiting nutrients contributes to environmental complexity

What are the two ways forest diversity is organized, and what drives the number of communities?

1. Within-community diversity: A large number of species live within most individual tropical forest communities.

2. Between-community diversity: A large number of plant communities exist within a given area, each with its own unique species composition.

• Main Driver: Variation in soil influences the number of distinct communities

What produces differences in vegetation of short distances?

Soil type, nutrients, and depth to groundwater

Why can nutrient enrichment reduce environmental complexity/species diversity?

Competition is the most likely as it increases competitive exclusion.

Sometimes biotic factors, not always abiotic factors (like space and light monopolization)

True or False: The highest number of species of plants are found in areas with lowest soil fertility

True. Increasing nutrient availability increases competition which decreases diversity

What is an example of nutrient enrichment reducing environmental complexity/species diversity?

Fertilization has decreased plant diversity and evenness over time. Becoming steeper/less even over time

Plant diversity has progressively declined since the beginning of long-term fertilizing

Shows effects of fertilizer, agriculture, and environmental conditions

Disturbance define

A discrete, punctuated killing, displacement, or damaging of one or more individuals or colonies that directly or indirectly creates an opportunity for new individuals or colonies to become established

True or False: Disturbance is consistent from organism to organism and environment to environment

False: Disturbance varies from organism to organism and environment to environment. Disturbance for one organism may not be one for another.

What levels of disturbance promote higher diversity? Why

Intermediate levels of disturbance promote higher diversity

Low levels of disturbance allow competition to reduce diversity

High levels of disturbance reduce diversity

What are potential source of disturbance?

Abiotic factors (Fire, hurricanes, floods, etc)

Biotic factors (Disease, predation, etc)

Human-caused disturbances

Discuss examples of disturbance and diversity

Algae and invertebrates

• Diversity of algae and invertebrates growing on boulders in the intertidal zone

• Boulders supporting the greatest diversity of species were those subject to intermediate levels of disturbance

Prairie dogs and North American prairies

• Prairie dogs build burrow systems and remove vegetation around burrows, which opens areas to plant colonization.

• Disturbance by prairie dogs creates distinctive patches of vegetation

Human caused

• Typically are high levels and lead to a decrease in diversity

• Deforestation & Pollution

What are ways that humans pollute?

Nitrates and phosphates from fertilizers enter water systems

• Leads to eutrophication

Toxic pollutants from industrial and urban areas

Plastics

What are Persistent Organic Pollutants (POPs)

They remain in the environment for decades/centuries

They resist environmental breakdown via biological/chemical/photolytic processes

What are examples of pollution in regards to animals

Beluga whales

• Most toxic mammal in western hemisphere

• Very saturated with agricultural run-off chemicals like pesticides

• Leads to immune system dysfunction correlated to mass die-offs and suggestive of broad environmental distress

Orcas

• PCB contamination of orcas which makes whales more vulnerable to infectious disease and impedes normal growth and development

Discuss biological magnification and pollution

Biological magnification concentrates industrial wastes and pesticides as they pass through the food chain.

Top-level predators are usually organisms most severely damaged by toxic compounds in the environment

Discuss microplastics and pollution

Microplastics are small enough to be eaten by zooplankton

Microplastics are too small to be captured by wastewater treatment plants, and end up in the sea

Discuss urbanization and diversity. Use examples

Urbanization can reduce bird species richness and evenness, but some landscapes still have substantial levels of diversity

Bird species richness peaks with intermediate land-use intensity

• Highest species richness occurred at intermediate levels of land-use intensity

• The number of native woodland bird species declines with increased land-use intensity

• Levels of similarities between study sites increased with degree of urbanization

Exploitation define

Interaction that enhances the fitness of one individual while reducing fitness of exploited individual

What are the 3(4) types of exploitation

Predators

Parasites

• Parasitoid

Pathogens

What do predators, parasites, and pathogens have an influence on?

Distribution, abundance, and structure of prey populations

Discuss herbivore predation/exploitation examples

• Herbivorous Stream Insect Larvae influence on algal and bacterial populations

  • Creating controlled comparison of grazed/ungrazed surfaces using manipulated stream rocks:

    • Allowing larvae to graze on some rocks

    • Excluding larvae from other rocks

  • Showed that larvae reduced the abundance of algal/bacterial populations

  • Chlorophyll a (indicating algal biomass) increased quickly during the first 2 weeks

  • As the larvae colonized, the algal biomass declines

  • Excluding the larvae increased the number of bacteria and increased algal biomass

• Bats/Birds’ effect on tropical forest arthropods

  • Birds exclusion increased arthropods by 65%

  • Bat exclusion increased arthropods by 150%. Bats have bigger effect

Dicuss pathogenic parasite effects on predators and prey examples

• Mange Mites on foxes and their indirect effects on foxes’ prey

  • Mange mites weaken foxes, often causing death. Infected fox populations decline sharply

    • Population of fox prey increased

    • Prey species expanded area distributions

    • Vegetation and lower trophic levels decreased due to increased prey species

Discuss examples of trophic cascades

• Mange Mites on foxes and their indirect effects on foxes’ prey

  • Mange mites weaken foxes, often causing death. Infected fox populations decline sharply

    • Population of fox prey increased

    • Prey species expanded area distributions

    • Vegetation and lower trophic levels decreased due to increased prey species

Discuss the predator/prey cycles and dynamics

Predator-prey relationships are cyclic because populations of predators and prey rise and fall in repeating patterns. They are dynamic because the patterns constantly shift with environmental conditions, resource availability, and species interactions

Why do predator-prey cycles happen?

• When prey populations increase: predators have more food & predator numbers rise

• As predator numbers rise: prey are eaten more quickly & prey numbers fall

• With fewer prey: predators starve or reproduce less & predator numbers fall

What is an example of predator/prey cycles.

Discuss role of food supply and role of predators

Lynx and snowshoe hare cycles

• Show long-term cycles in population density since 1850s

• Role of food supply

  • In winter, hares eat buds and stems of shrubs.

  • Shoots produced after browsing have increased levels of chemical defenses, which reduces usasble food supplies during population declines

• Role of predators

  • Predation can account for 60-90% of hare mortality during peak densities

Why are predator-prey interactions dynamic? What causes them to change?

• Climate shifts alter food availability

• Disease affects either predator or prey

• Habitat changes modify hunting success

• Human impacts (hunting, land use) disrupt patterns

• New predators or competitions enter the system

True or False: Predator-prey systems are typically static

False. Predator-prey systems are always adjusting to new conditions

What are the predator/prey ecological important cyclic and dynamic interactions

• Regulate population size

• Prevent any one species from dominating

• Maintain biodiversity

• Influence energy flow through ecosystems

Discuss an example of food and predation impacts on prey

Hares, Predators, and Plant food supply

• Found increased hare numbers with:

  • Increased food availability

  • Reduced predation

  • Combination of two

• Concluded that the hare population cycle results from interactions among 3 trophic levels: hares, their plant food supply, and their predators

What does the Lotka-Volterra assume?

Assumes host (prey) population grows exponentially, and population size is limited by parasites, pathogens, and predators

What is this equation for?

Define the variables

Growth of Prey (host) populations

r_hN_h = exponential growth by host population, which is opposed by:

p = rate of parasitism/predation

N_h = Number of hosts

N_p = Number of parasites/predators

What is this equation for?

What are the variables?

Growth of predator populations

cpN_hN_p = conversion rate of hosts into parasite/predator offspring

• c is the conversion factor

• p is the rate of parasitism/predation

• N_h = Number of hosts

• N_p = Number of parasites/predators

d_pN_p = parasite/predation deaths

Draw a graph of Lotka-Volterra Predator-Prey model with axises names

Draw a graph of Lotka-Volterra Predator-Prey model with the removal of time with axises names

What are the seven unrealistic assumptions of the Lotka-Volterra Predator-Prey model

1. Prey population grows exponentially in the absence of predators

2. Predator population declines exponentially without prey

3. Predators consume prey at a rate proportional to prey density

4. No predator interference or competition

5. Environment constant

6. No age structure or spatial structure

7. Predator and prey interact continuously

What are the issues with the Lotka-Volterra model?

It predicts perfect, regulat cycles which are rare in nature

It cannot explain stability, chaos, or dampened oscillations

Ignores density dependence, functional responses, and refuges

Discuss an experiment regarding the Lotka-Volterra

• Interactions between adzuki bean weevil and parasitoid wasps that attack bean weevil

• Successfully produced regular, repeating cycles for over 112 generations

  • As prey increased → predators increased

  • As predators increased → prey decreased

  • As predator decreased → prey rebounded

Why have most laboratory experiments failed to produce L-V oscillations

Refuges

Discuss mites experiment and the importance

• REGUFE

• Prey: Six-spotted mite

• Predator: Predatory mite

• Array of 120 oranges with barriers that left 5% of the orange area exposed to the mites

• Importance:

  • Spatial structure is essential for stable predator-prey dynamics

  • Real ecosystems are not simple boxes—they are patchy and complex

  • Predator-prey cycles depend on refuges, dispersal, and heterogeneity

  • Lotka-Volterra cycles are more realistic when space included

What are forms of refuges?

Trees, Water, Burrows, Flight, Size (Bigger), Space

Discuss an example of space refuges

Invasive cactus have a small isolated population as a spatial refuge, so herbivorous insects can’t find them

Discuss the five reasons for that high population density can act as a refuge

1. Safety in numbers (dilution effect)

2. Predator confusion

3. Predator satiation

4. Reduced per capita risk

5. Group defense

What is the ecology of fear.

The ecology of fear describes how prey change behavior, physiology, and distribution simply because predators might be present, even with predators aren’t actively killing them

What are the two ways predators influence prey? Describe them

Direct: Killing prey

Indirect: Fear alters prey behavior, reducing feeding, reproduction, or habitat use

Why does fear matter in prey? What does it do?

• Reduces prey feeding

• Shifts prey into safer but less productive habitats

• Lowers reproduction

• Increases stress hormones

• Changes movement patterns

• Alters group size

Discuss an example of ecology of fear and refuges

Wolves and elk

• When wolves returned to Yellowstone:

  • Elk avoided risky riverbanks

  • Vegetation rebounded

  • Beavers increased

  • Songbirds returned

• It was caused because elk feared wolves and changed where they grazed

• Fear reshaped the landscape

Discuss examples of parasites/Pathogens that manipulate host behavior

• Spiny-headed worms change the behavior of amphipods by making it more likely that the infected amphipods will be eaten by vertebrate hosts

  • Uninfected amphipods exhibit negative phototaxis (away from light), away from suitable vertebrate hosts

  • Infected amphipods exhibit positive phototaxis (towards light), which puts them closer to surface predators

  • Cycle:

    • Adult female worm lays eggs in bird intestines, bird has infected feces

    • Isopod eats the feces with eggs, those eggs hatch in hours, and mature in 60 days

    • Mature larvae alter isopod behavior making it go out into the open

    • Isopod is eaten by bird and the worm attaches to intestines of bird

Discuss pest control with bats

• Adult female bats consume 2/3 its body weight in insects including moths, who caterpillars attack cotton fields

• Pest control by bats saves the farmers over a million annually

Define variables of population growth equation

N_t = N_t-1 + B + I - D - E

N_t = Population size/density at time

N_t-1 = Population size/density at previous time

B = Births

I = Immigration

D = Deaths

E = Emmigration

Population dynamics definition

Concerned with factors influencing expansion, decline, and maintenance of populations

African Honeybees differentiation

• Dispersed incredibly quickly through most of South American, Mexico, and all of Central America

• High rates of colony formation and dispersal caused rapid expansion of African Honey bees

How are dispersal and local population densities related

Dispersal can increase or decrease local population densities

Eurasian Collared Doves dispersal

• Spread from Turkey to almost all of Europe after 1900 in small jumps

• Introduction in Barbados in the 1970s led to rapid dispersal, reaching North America by the 1980s/90s

• Most fledglings disperse a few kilometers, but some disperse hundreds of kilometers

• Adults are sedentary; young disperse

What two animals have high rate of expansion/dispersal?

Africanized honeybees and Eurasian collared doves

Discuss the reason for northward dispersal

• Organisms began to move northward around 16,000 years ago after the retreat of glaciers and warming climate

• Evidence found in pollen in lake sediments

Discuss tree expansion

Maple trees and hemlock trees have been moving upward from low/mid USA up to Canada over the past 12,000 years

Discuss dispersal in response to changing food supply

• Increased prey density leads to increased density of predators

Discuss dispersal in rivers and streams

• Streamlined bodies

• Bottom-dwelling

• Adhesion to surfaces

Define spates. What is it related to?

Spates: Sudden flooding in a stream

Related to dispersal in rivers/streams