Ecology Exam 2 Jeop

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