Biology Exam 2 Review: Nitrogen Cycling and CNDD

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Questions and Answers

What does conspecific negative density dependence (CNDD) help maintain in forest communities?

Growth of dominant species

Increase in population density

Reduction of natural enemies

Species diversity (correct)

According to the Janzen-Connell hypothesis, where are host-specific natural enemies primarily found?

Near abundant host plant species (correct)

In areas with high plant diversity

Within monoculture plantations

In areas of low species density

What is a key idea behind the green world hypothesis?

Herbivores significantly aid plant growth

Predators help control herbivore populations (correct)

Predators play no role in ecosystem regulation

Ecosystems thrive without any trophic interactions

What is defined as the phenomenon where apex predators regulate the population of plants/producers?

Trophic cascade Signup and view all the answers

What role do ecosystem engineers play within an ecosystem?

They create, modify, or maintain habitats Signup and view all the answers

Which of the following best describes a mutualistic relationship?

Both species benefit from the interaction Signup and view all the answers

What is the distinction between stress and disturbance in ecological terms?

Stress involves external constraints on primary productivity; disturbance is a discrete event disrupting ecological structure. Signup and view all the answers

What characterizes a mycorrhizal relationship?

Mutual benefit between a plant and a fungus Signup and view all the answers

What is the primary factor that determines the limits of forests?

Temperature, soil/edaphic controls, and winter damage Signup and view all the answers

What type of mycorrhiza improves the host plant's nitrogen nutrition?

Ectomycorrhiza Signup and view all the answers

What does the term 'krummholz' refer to in the context of trees?

Small, deformed trees found in harsh climatic conditions. Signup and view all the answers

In which environments are endomycorrhizae commonly found?

Agricultural and forest soils Signup and view all the answers

Which process refers to a tree reaching a size that increases its chances of surviving to maturity?

Establishment Signup and view all the answers

What is a crucial aspect of symbiotic relationships?

Close physical association between organisms Signup and view all the answers

What occurs as a result of adiabatic cooling at higher altitudes?

Reduction in air temperature. Signup and view all the answers

In alpine ecosystems, what is typically true about the relationship between plant proximity and stress?

Low stress environments encourage competition for resources and greater distances. Signup and view all the answers

What are the two main factors that influence the success of tree establishment at treelines?

Multiple controls acting on growth and establishment vary by location and species. Signup and view all the answers

Which term best describes the transitional zone between forest lines and treelines?

Alpine treeline ecotone Signup and view all the answers

What is the main difference between growth and establishment of trees?

Growth is the accumulation of biomass, while establishment relates to survival probability. Signup and view all the answers

What is the role of ectomycorrhizal fungi in relation to root nodules on an alder tree?

They are responsible for nitrogen fixation through bacteria. Signup and view all the answers

What type of succession occurs after a disturbance such as a wildfire?

Secondary succession Signup and view all the answers

What process describes the breakdown of polymers into smaller molecules?

Depolymerization Signup and view all the answers

How do soil microbes interact with nutrient availability for plants?

They can both compete and immobilize nutrients. Signup and view all the answers

What is called when precipitation collects nutrients while moving through the canopy?

Throughfall Signup and view all the answers

What percentage of the global nitrogen budget comes from lightning?

5-8% Signup and view all the answers

What characterizes a keystone species in an ecosystem?

It has a disproportionate ecological effect relative to its biomass. Signup and view all the answers

What is the process called when microorganisms convert inorganic nutrients into organic forms?

Immobilization Signup and view all the answers

What is the main function of mineralization in soil ecosystems?

Transforming organic matter into inorganic nutrients for plant use Signup and view all the answers

Which of the following statements is true about the common mycorrhizal network?

It connects multiple plant species through fungus. Signup and view all the answers

Study Notes

Exam 2 Review

Nitrogen Cycling: Review chapter 18 on nitrogen cycling. Extensive material covered in the Tuesday before Thanksgiving lecture.
Conspecific Negative Density Dependence (CNDD): A process where population density negatively impacts growth, survival, and recruitment of the same species. This can maintain species diversity in an area by allowing other species to replace the common species. Conversely, as population density increases, individual growth, survival, and reproduction of each species within that population decrease.

Janzen-Connell Hypothesis

Explanation: This hypothesis proposes that natural enemies (pathogens, predators) are concentrated where host plant species are most dense. This leads to reduced survival of seedlings close to parent trees or other conspecifics. Specialist pathogens are key in this negative density dependence, not generalist pathogens.
Prediction: Stronger density-dependent and distance-dependent effects on plant richness in wetter habitats and the tropics, compared to drier habitats and temperate zones.

Vertebrate Herbivores & Predation

Green World Hypothesis: Predators regulate consumer (herbivore) populations, preventing overconsumption and maintaining plant abundance in ecosystems. This is a critical counterpoint to the previously held assumption that predators had no major impact on ecosystem regulation and stability.

General Ecological Concepts

Trophic Cascades: Changes in the abundance of top predators can have cascading effects through the food web, impacting multiple trophic levels.
Ecosystem Engineers: Organisms that create, modify, or maintain habitats. Beavers, coral, and termites are examples. These organisms significantly impact ecosystem structure and processes.
Symbiosis: Long-term, close relationships between organisms. Different types exist, including mutualism (both benefit), parasitism (one benefits, one harmed), and commensalism (one benefits, other unaffected). Lichen and bees illustrate examples of mutualism. Dwarf mistletoe is an example of parasitism.
Mycorrhizae: Symbiotic relationships between fungi and plant roots, greatly increasing nutrient uptake for plants. Endomycorrhizae affect a wide range of plants while ectomycorrhizae are specifically found in agricultural and forest soils, impacting a range of hardwood and conifer species. Fungi derive carbon from plants, while plants receive water and nutrients from fungi.
Common Mycorrhizal Network: Root systems of multiple plants connected through a network of mycorrhizal fungi.
Keystone Species: A species disproportionately affects its local ecosystem relative to its abundance. Effects can be significant enough that their removal may be devastating to an ecosystem.

Additional Concepts

Throughfall: Precipitation that passes through the canopy.
Stem Flow: Water that flows down plant stems and carries nutrients and organic material.
Treeline: Edge of forests where trees grow less commonly and density decreases due to harsh environmental conditions, such as low temperature, and dry conditions.
Krumholz: Short, stunted, and dense trees often found at the alpine treeline.
Alpine Treeline Ecotone: Transition zone between forest and treeline.
Dispersal: Ability of plants to reach new habitats.
Germination: Process of seeds sprouting.
Establishment: A plant successfully taking root in a new habitat.
Growth: A plant's expanding size and biomass.
Stress vs. Disturbance: Stress refers to external constraints on primary productivity while disturbance impacts structure, substrate, and resources available to organisms.
Growth vs Establishment: Establishment is size- and life stage-related while growth is biomass accumulation.
Adiabatic Cooling: Temperature decrease with altitude due to decreasing atmospheric pressure.

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Description

Prepare for your biology exam with this comprehensive review of Chapter 18 on nitrogen cycling, and explore the concept of Conspecific Negative Density Dependence (CNDD). Understand how population density affects species growth and diversity, as well as the Janzen-Connell Hypothesis and its implications for plant communities. This quiz will enhance your grasp of these critical ecological concepts.