Envi Sci Week 1

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Questions and Answers

What factors primarily influence population size?

Geographical location, seasonal changes, predator presence

Reproductive strategies, symbiotic relationships, habitat space

Resource availability, competition, interspecific interactions (correct)

Population size, weather, genetic variation

Which of the following best describes density-dependent fluctuation?

Variations in population size caused by natural disasters

Changes in population size due to environmental conditions

Fluctuations in population size due to food scarcity

Population changes related to the density of another population (correct)

What is the carrying capacity of an environment?

The maximum number of individuals an environment can sustain (correct)

The minimum resource availability necessary for survival

The maximum growth rate of a population

The number of births occurring in a population over time

Which characteristic is associated with K-selected species?

Delayed reproduction and long lifespan (C) Signup and view all the answers

What is the primary focus of ecology?

Understanding the interactions of living organisms with each other and their environment (D) Signup and view all the answers

Which term describes the interaction within a community that affects population sizes?

Interspecific interactions (C) Signup and view all the answers

An example of a density-independent factor affecting population size is:

Natural disasters like fires (C) Signup and view all the answers

Which life history strategy typically favors rapid reproduction in harsh environments?

R-selected strategy (A) Signup and view all the answers

What defines the Gross Primary Production (GPP) in an ecosystem?

The total amount of photosynthesis occurring in the system (C) Signup and view all the answers

How is Net Primary Production (NPP) calculated?

NPP = GPP - R (A) Signup and view all the answers

What role do decomposers play in an ecosystem?

They break down organic matter (A) Signup and view all the answers

Which of the following environments has the highest ecosystem productivity in terms of NPP?

Tropical forests (D) Signup and view all the answers

In an ecosystem, what term describes the various levels a species occupies in the food web?

Trophic levels (B) Signup and view all the answers

What is the main source of primary production in the oceans?

Phytoplankton (A) Signup and view all the answers

What is the significance of 'source' and 'sink' in biogeochemical cycles?

They describe areas that produce or remove elements from cycles (A) Signup and view all the answers

What factor primarily controls productivity in ocean ecosystems?

Light and nutrients (A) Signup and view all the answers

What is the primary effect of fossil fuel emissions on atmospheric CO2 levels over the last century?

Increase in CO2 concentration (D) Signup and view all the answers

Which of the following is a significant reservoir for carbon in the carbon cycle?

Atmosphere (D) Signup and view all the answers

What is meant by the term 'net sink' in relation to the carbon cycle?

More carbon enters than leaves a reservoir (B) Signup and view all the answers

Why is nitrogen essential for living organisms?

It is a constituent of essential biomolecules like proteins and DNA (C) Signup and view all the answers

How does nitrogen primarily enter the soil for plant use?

Through fixation by bacteria and decomposition processes (C) Signup and view all the answers

What is denitrification in the nitrogen cycle?

Conversion of nitrate to atmospheric nitrogen (D) Signup and view all the answers

Which of the following interactions in communities is characterized by competition?

Both species are negatively affected (D) Signup and view all the answers

What role do humans play in the nitrogen cycle?

They introduce nitrogen primarily through fertilizer use (B) Signup and view all the answers

Study Notes

Environment and Ecology

Environment: the habitat where organisms live, consisting of biotic (living) and abiotic (non-living) components.
Ecology: the study of interactions between organisms and their environment.

Ecosystems and Communities

Ecosystem: includes biological communities and abiotic components (e.g., rock, air, water, soil) along with energy and matter fluxes.
Population: a group of similar organisms in a specific area at a given time.
Community: an interaction of multiple populations within the same environment.

Population Dynamics

Change is constant in nature with all components interconnected.
Factors affecting population size include:
- Resource availability (food, water)
- Competition for limited resources among individuals
- Interspecific interactions (predation, parasitism)
- Environmental conditions (weather, natural disasters)

Population Fluctuations

Density-dependent fluctuations: population size changes based on the density of another population (e.g., predator-prey interactions).
Density-independent fluctuations: population size changes in response to environmental factors (e.g., climate, fire).

Carrying Capacity

Carrying capacity (K): maximum sustainable population size where births equal deaths.
Known as density-dependent equilibrium.

Life History Strategies

R-selected species: focus on rapid reproduction in harsh environments; characteristics include quick development, small body size, many offspring, minimal parental care (e.g., American toad).
K-selected species: emphasize growth and survival in stable environments; characteristics include slow development, larger size, fewer offspring, substantial parental care (e.g., bears).

Energy Flow and Photosynthesis

Energy flow in ecosystems starts with photosynthesis, where green plants convert solar energy into chemical energy.
Biomass represents the organic matter, measured in grams of carbon per square meter per year (gC/m²/yr).

Primary Production Metrics

Gross Primary Production (GPP): total photosynthesis in an ecosystem.
Net Primary Production (NPP): the balance of photosynthesis minus respiration (NPP = GPP - R).

Trophic Levels and Food Webs

Autotrophs (primary producers): organisms that perform photosynthesis.
Heterotrophs: consumers of other organisms (herbivores as primary consumers, carnivores as secondary consumers).
Decomposers: organisms that break down dead organic material.
Food webs represent interconnected food chains and trophic levels within ecosystems.

Ecosystem Productivity

Ecosystem productivity varies by region, with tropical forests showing the highest (1000-3500 g/m²/year) and tundras the lowest (100-250 g/m²/year).
Microscopic algae (phytoplankton) are primary producers in ocean ecosystems.

Biogeochemical Cycles

Biogeochemical cycles involve the movement of chemical elements between living and non-living parts of the environment.
Sources produce elements, while sinks remove them. Flux indicates movement between sources and sinks.

Carbon Cycle

Major reservoirs of carbon: atmosphere, land (biosphere and lithosphere), oceans; fossil fuels act as a fourth reservoir.
Atmospheric CO₂ concentration has risen from 280 ppm to over 400 ppm primarily due to fossil fuel emissions.

Nitrogen Cycle

Nitrogen is crucial for proteins, DNA, RNA, and chlorophyll, making it essential for life.
Despite its abundance in the atmosphere (78%), nitrogen must be converted to usable forms for organisms.
Nitrogen fixation converts inert atmospheric nitrogen into forms that plants can absorb.
Decomposition of dead organisms returns nitrogen to the soil, while denitrification converts nitrates back to atmospheric nitrogen.
Human activity, specifically fertilizer use, adds nitrogen to the cycle.

Interspecific Interactions

Various interactions in communities:
- Predation: (+/-) one species benefits at the expense of another.
- Parasitism: (+/-) one organism benefits, harming the other.
- Competition: (-/-) both species are harmed by sharing limited resources.
- Commensalism: (+/0) one species benefits while the other is unaffected.
- Mutualism: (+/+) both species benefit from the interaction.

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