Envio. Bio Unit 2 flashcards

Key Concepts in Population Ecology

Population Ecology is the study of how populations of species interact with their environment, focusing on factors like birth and death rates, immigration, and emigration. Here’s a breakdown of the key points:

Population

• Definition: A population consists of organisms of the same species living in a specific geographic area at the same time, capable of interbreeding.

Population Growth Patterns

1. Arithmetic Growth

   • Growth increases at a constant rate (e.g., the same number of individuals added each generation).

   • Not realistic for long-term population growth.

2. Exponential Growth

   • Growth accelerates with each generation, often seen in environments with abundant resources.

   • Also not sustainable long-term due to resource limitations.

   • “J”-shaped curve represents this growth pattern.

3. A Third Realistic Growth Pattern

   • This pattern accounts for environmental constraints and is more realistic (likely referring to logistic growth).

Population Growth Rate

• Formula:
  
  

• Doubling Time:
  
  

• Example:

  • Current human population: 8.1 billion.

  • Growth rate: 1.1%.

  • Doubling time: 

  •  years.

  • Estimated population of 16.2 billion by 2086.
    
    

Case Study: European Starlings

• Background: 60 starlings released in NYC in 1890.

• Growth:

  • Tens of thousands by 1900.

  • Millions by the 1920s.

  • Spread across the U.S. by 1970.

• Why Exponential Growth?

  • Abundant resources and lack of competition initially.

• Why Not Sustained?

  • Resource limitations, competition, and environmental constraints.

Why Exponential Growth Isn’t Realistic Long-Term

• Exponential growth assumes unlimited resources, which is not the case in real ecosystems.

• Populations eventually face limiting factors like food, space, and predation, leading to logistic growth (S-shaped curve).

Questions for Reflection

1. Why do populations rarely grow exponentially in nature?

2. What factors would limit human population growth?

3. How might we manage resources to support a growing population?

Population Growth and Limits

1. Carrying Capacity (K):

   • The maximum number of organisms an environment can sustainably support.

   • Determined by available resources like food, space, and water.

2. Logistic Growth:

   • Population growth follows an “S-shaped curve” (logistic curve) when resources are limited.

   • Growth is rapid when the population is small but slows as it approaches carrying capacity

3. Environmental Resistance:

   • Factors like competition, predation, and resource depletion reduce population growth.

   • As resources deplete, birth rates decrease and death rates increase.

4. Range of Tolerance:

   • The range of environmental conditions (e.g., temperature, nutrients) within which an organism can survive and reproduce.

Habitat and Niche

1. Habitat:

   • The physical environment where an organism lives (its “address”).

2. Niche:

   • The role an organism plays in its ecosystem (its “career”), including its interactions with biotic and abiotic factors.

Survivorship

• Survivorship Curves:

  • Type I: Most individuals die at an old age (e.g., humans).

  • Type II: Equal mortality rates across all ages (e.g., birds).

  • Type III: High mortality among young individuals (e.g., fish).

Questions to Consider

• Can organisms exceed their carrying capacity?

  • Yes, but this leads to resource depletion, increased mortality, and a population crash.

Evolution

1. Definition:

   • Genetic changes in a population over time (individuals do not evolve).

   • “Descent with modification” (Charles Darwin).

2. Types of Evolution:

   • Adaptive Evolution:

     • Species become better suited to their environment (e.g., natural selection).

   • Non-Adaptive Evolution:

     • Changes not driven by environmental suitability (e.g., genetic drift, artificial selection).

3. Mutation:

   • Random changes in DNA that provide the raw material for evolution.

4. Unifying Concept in Biology:

   • Evolution explains the diversity of life and the relationships between organisms.

Genetic Drift and the Founder Effect:

Genetic Drift is a mechanism of evolution where random events cause changes in the frequency of inherited traits in a population. It is more pronounced in small populations because chance events have a larger impact on the gene pool. Genetic drift is a non-adaptive and random process, meaning it is not driven by natural selection or fitness advantages.

The Founder Effect is a specific type of genetic drift. It occurs when a small group of individuals becomes isolated from a larger population, leading to a new population with reduced genetic diversity. The gene pool of the new population is determined by the genes of the founding individuals, which may not represent the diversity of the original population.

Activity: Colonizing Mars

Imagine sending a small group of 10 people from the diverse population of the United States to Mars to start a new colony. Here’s what to consider:

1. Diversity in the Colony vs. the US:
   The colony would have significantly less diversity compared to the US because it is founded by only 10 individuals. Their genetic makeup would represent a tiny fraction of the genetic diversity found in the US population.

2. Diversity in Future Generations:
   As the colony grows and has children, the genetic diversity would remain limited. The gene pool would be shaped by the alleles present in the founding group, and random genetic drift could further reduce diversity over time. This would likely result in a population that is less diverse than the US.

3. Risks and Issues:

   • Reduced genetic diversity could lead to a higher risk of inherited diseases and reduced adaptability to environmental changes.

   • Genetic drift could cause certain traits to become more common purely by chance, even if they are not advantageous.

   • The small population size could also make the colony more vulnerable to extinction due to random events like disease or environmental disasters.

Is This Situation Realistic?

Yes, the Founder Effect is a realistic phenomenon observed in nature. Examples include:

• Amish and Mennonite communities, which have high frequencies of certain genetic disorders due to their small founding populations.

• Island species, where a small group of individuals colonizes a new habitat and evolves into a distinct population.

Evolution of Species and Reproductive Isolation:

A species is defined as a group of organisms that can interbreed and produce fertile offspring. Speciation occurs when populations become reproductively isolated and evolve independently. Reproductive isolation can occur through:

1. Geographic Isolation:
   Physical barriers like mountains or rivers prevent populations from interbreeding.

2. Temporal Isolation:
   Populations breed at different times (e.g., different seasons).

3. Behavioral Isolation:
   Differences in courtship rituals or mating behaviors prevent interbreeding.

4. Structural Isolation:
   Physical differences in reproductive structures prevent mating.

Reproductive isolation can lead to the evolution of new species over time. Hybrids between species (e.g., mules) are often sterile, maintaining the separation of species.

Human Effects on Evolution and Extinction:

Humans influence evolution through:

1. Artificial Selection:
   Selective breeding of plants and animals to enhance desirable traits.

2. Extinction:
   Human activities like habitat destruction, pollution, and overharvesting have accelerated the rate of species extinction.

Extinction is the permanent disappearance of a species. While extinction is a natural process, human activities have caused extinction rates to exceed natural levels, leading to a biodiversity crisis.

Summary:

• Genetic Drift and the Founder Effect highlight the role of chance in shaping populations, especially in small groups.

• Reproductive Isolation is a key factor in the evolution of new species.

• Humans play a significant role in influencing evolution and extinction through artificial selection and environmental impacts.

Extinction and Speciation

1. Extinction:

   • Over 99% of all species that ever lived have gone extinct.

   • Mass extinctions: Occur in a short period and are planet-wide (e.g., the five major extinction events in Earth’s history).

   • Background extinction: The natural, ongoing rate of extinction between mass extinctions.

   • Species that fail to adapt to changing environments face extinction.

2. Current Extinction Crisis:

   • Humans may be causing a 6th mass extinction.

   • The current extinction rate is 100-1000 times higher than the historical background rate, primarily due to habitat destruction, pollution, climate change, and overexploitation of resources.

Human Population Growth

1. Historical Growth:

   • Pre-agricultural period (100,000 years ago):

     • Slow growth, doubling time in tens of thousands of years.

     • Population: 5-10 million by the end.

   • Agricultural period (10,000 years ago):

     • Domestication of plants and animals increased food production and carrying capacity.

     • Doubling time: ~1,000 years.

     • Population: ~500 million by the end.

   • Industrial period (1700-1800):

     • Technological advances, fossil fuels, sanitation, and healthcare reduced death rates.

     • Current population: 8.1 billion.

     • Doubling time: Decades.

2. Carrying Capacity:

   • Technology and social interactions have expanded the planet’s carrying capacity for humans.

   • However, this growth has come at the cost of environmental degradation and biodiversity loss.

Demographic Transition Model

This model explains how human population growth changes as societies develop economically and socially:

1. Stage 1: Pretransition (Preindustrial):

   • High birth and death rates.

   • Limited resources and widespread disease.

2. Stage 2: Mortality Transition:

   • Death rates drop due to better healthcare and technology.

   • Birth rates remain high, leading to rapid population growth.

3. Stage 3: Fertility Transition (Industrial Stage):

   • Birth rates decline as people have fewer children and start families later.

   • Population growth slows.

4. Stage 4: Stability Transition (Post-industrial Stage):

   • Low birth and death rates.

   • Zero or negative population growth.

Demographic Factors Influencing Population Growth

1. Economic Conditions:

   • Wealthier countries tend to have lower birth rates.

2. Education:

   • Increased education, especially for women, correlates with lower fertility rates.

3. Healthcare:

   • Improved healthcare reduces infant mortality and increases life expectancy.

   • Paradoxically, while healthcare initially increases population size, it can eventually slow growth by reducing the need for large families.

Discussion Points

1. Education and Healthcare:

   • Education empowers individuals to make informed family planning decisions.

   • Healthcare reduces infant mortality, decreasing the incentive for larger families.

2. Healthcare’s Dual Role:

   • While healthcare can increase population size initially, it leads to lower birth rates in the long term as societies stabilize.

3. Human Population Control:

   • Unlike in nature, where predators regulate populations, humans must rely on social, economic, and environmental strategies to manage growth sustainably.

Key Takeaways

• The current rate of extinction is alarmingly high, largely driven by human activities.

• Human population growth has accelerated due to technological and agricultural advancements, but this growth is unsustainable without addressing environmental impacts.

• The Demographic Transition Model offers a framework for understanding how economic and social development can stabilize population growth.

• Education, healthcare, and economic development are critical tools for achieving sustainable population levels and mitigating environmental harm.

Today’s agenda and the accompanying notes cover important topics related to human population dynamics, ecological footprints, and sustainability. Here’s a breakdown of the key points and activities:

Today’s Agenda

1. Human Populations: Discussion of factors influencing population growth, including education, health care, and global variations in birth and death rates.

2. Quiz 4: Opens after class today and is due before class starts on Wednesday. It will include evolution material not covered in previous quizzes.

3. Unit 2 Exam: Scheduled for one week from today (Monday, 2/24).

Activity: Education and Health Care in Population Growth

• Discussion Topics:

  • Why education and health care can slow down population growth.

  • How improved health care, while often increasing population sizes, can also contribute to slowing population growth.

  • The role of societal factors in shaping fertility and population dynamics.

• Key Points:

  • Poor Nations:

    • Lack of education and health care leads to early and frequent childbirth, small gaps between births, and reliance on children for elder care.

  • Wealthy Nations:

    • Access to contraception, family planning, and education empowers women to make informed fertility decisions, delay childbirth, and have fewer children.

    • Reduced reliance on children for elder care.

Global Variations in Growth

• Factors Influencing Population Growth:

  • Birth (fertility) rates, infant death rates, death rates, life expectancy, and age structure.

• Age Structure:

  • Determined by survivorship and age-specific birth rates.

  • Age-structure pyramids visually represent population growth trends:

    • High birth rate, low survivorship: Rapid growth.

    • Low birth rate, high survivorship: Stable population.

    • Low birth rate, aging population: Population decline.

Human Population Growth

• Current Population: 8.1 billion (as of 2024).

• Projected Growth: Expected to reach 9 billion within 15 years.

• Challenges:

  • Rapid population growth over the last 250 years.

  • Environmental issues linked to population growth and resource consumption.

  • Disparities in resource use and access between countries.

Ecological Footprint

• Definition: The area of land required to supply resources consumed by a population.

• Components: Includes land for food, housing, energy, and waste disposal (water and waste disposal are critical but often not shown in calculations).

• Global Variations:

  • The USA has an ecological footprint of 8.6 global hectares (gha) per person, but only 3.8 gha is available per person, indicating unsustainability.

  • Ethiopia, in contrast, faces severe water scarcity, with only 13% of the population having access to clean water and rural residents using just 6.5 gallons of water per day.

Sustainability vs. Carrying Capacity

• Carrying Capacity: The maximum population size an environment can support.

• Sustainability: Maintaining a population below carrying capacity to ensure long-term resource availability.

• Human Impact: Current ecological footprints suggest that human populations are unsustainable long before reaching carrying capacity.

Reflection Questions

1. How do education and health care influence population growth?

2. Why is improved health care both a driver and a brake on population growth?

3. How do ecological footprints vary between countries, and what does this mean for global sustainability?

4. What are the implications of water usage disparities between countries like the USA and Ethiopia?

This session highlights the interconnectedness of population dynamics, resource use, and sustainability, emphasizing the need for informed policies and practices to address global challenges.

Here’s a structured summary of the content provided:

Today’s Agenda (2/19/2025)

1. Finish Human Populations

2. Start Community Ecology

3. Unit 2 Exam: Monday, 2/24

   • Ensure you have a Scantron Form 4521.

   • Buy 5 at the bookstore and save them for later.

   • There are 4 unit exams and 1 final exam.

Biocapacity

• Definition: The area and quality of land available to supply resources.

• Ecological Debtors: Populations whose ecological footprints exceed their biocapacity must import goods.

  • Example: The USA (demand: 8.6 gha, supply: 3.8 gha).

• Ecological Creditors: Populations whose biocapacity exceeds their ecological footprint may export goods.

Topic 4: Community Ecology (Chapter 6.1-6.3)

• Definition: Examines how organisms in a community interact with each other and their environment.

• Key Focus: The organization and functioning of communities.

Terms

• Community: A group of populations of two or more different species occupying the same geographical area at a specific time.

Community Ecology

• Biotic Interactions:

  • Competition

  • Herbivory

  • Predation

  • Parasitism

  • Mutualism

  • Commensalism

Biotic Interactions and Their Effects

Competition

• Conditions for Competition:

  1. Two or more groups use the same resource.

  2. The resource is in short supply.

  3. The fitness of each group is reduced when they occur together.

• Impact: More energy and time are spent gaining fewer resources, which is a disadvantage for all involved.

Types of Competition

1. Exploitative Competition: Competitors consume or use the same limiting resource.

2. Interference Competition: Competitors deny each other access to the limiting resource.

3. Interspecific Competition: Between two different species.

4. Intraspecific Competition: Between members of the same species.

Competitive Exclusion Principle

• Two species that directly compete for resources cannot coexist.

  • Example: Paramecium aurelia vs. Paramecium caudatum.

How Can Competitors Coexist?

1. Ecological Niche:

   • Fundamental Niche: Complete range of areas where an organism could exist.

   • Realized Niche: Range where an organism actually exists due to competition.

2. Niche Differentiation: Division of resources to reduce competition.

Coevolution

• Definition: When two or more species reciprocally affect each other’s evolution through natural selection.

It looks like you’ve outlined the key topics for a biology or ecology class, focusing on community ecology and species interactions. Here’s a more organized summary of the content:

Today’s Agenda

1. Finish Community Ecology and the Unit

2. Unit 2 Exam Details

   • Date: Monday, 2/24

   • Required: Scantron Form 4521

   • Tip: Buy 5 at the bookstore and save them for future exams (4 unit exams + 1 final exam).

Community Ecology Topics

Herbivory

• Herbivores: Adapted to feed on plant material with specialized digestive systems.

• Coevolution: Plants evolve anti-herbivory defenses (chemical and mechanical), while herbivores evolve to detoxify plant chemicals.

• Avoiding Herbivory: Plants develop strategies to deter herbivores.

Predation

• Predators: Capture, kill, and consume prey.

• Prey Switching: Predators focus on the most abundant prey species.

• Coevolution: Predators evolve to detect and capture prey more efficiently, while prey evolve to avoid detection and capture.

• Avoiding Predation: Prey species develop strategies like camouflage, mimicry, or behavioral adaptations.

Parasitism

• Parasites: Depend on a living host for nourishment without immediately killing it.

  • Types: Ectoparasites (external) and endoparasites (internal).

• Vectors: Organisms that spread diseases or parasites without being significantly affected.

Mutualism

• Definition: Both species benefit from the interaction.

  • Examples: Figs and wasps, hippo cleaning stations, ants and bullhorn acacias.

Commensalism

• Definition: One species benefits, while the other is unaffected.

  • Examples: Barnacles and whales, cattle egrets and buffalos.

Circling Back to Extinction

• Invasive Species: Non-native species that harm the environment.

  • Outcompete native species for resources.

  • Lack natural predators, leading to uncontrolled population growth.

  • Some are predators that drive native prey species to extinction.

  • Some are artificially selected predators that have become feral.

Key Concepts

1. Coevolution: Reciprocal evolutionary changes between interacting species (e.g., herbivores and plants, predators and prey).

2. Species Interactions: Herbivory, predation, parasitism, mutualism, and commensalism shape ecological communities.

3. Conservation Concerns: Invasive species and their impact on native biodiversity and extinction rates.

Study Tips for the Exam

• Review the coevolutionary relationships and examples of each species interaction.

• Understand the ecological roles of invasive species and their consequences.

• Practice identifying examples of mutualism, commensalism, parasitism, herbivory, and predation.

Good luck on your exam!