Population and Community Ecology Notes

Population Ecology 2

Terrestrial Biomes

• Lists various terrestrial biomes including: ice sheet and polar desert, tundra, taiga, temperate broadleaf forest, temperate steppe, subtropical rainforest, Mediterranean vegetation, monsoon forest, desert, xeric shrubland, dry steppe, semiarid desert, grass savanna, tree savanna, subtropical dry forest, tropical rainforest, alpine tundra, and montane forests.

Life Table for Lacerta vivipara Females

• Table 54.1 presents a life table for Lacerta vivipara females in the Netherlands.
• It includes age class (x), number of survivors (Nx), survivorship (lx), age-specific fecundity (mx), and the product of survivorship and fecundity (lxm_x).
• Net reproductive rate (R_0) is calculated as 1.00.

Population Growth Parameters

• R_0: Net reproductive rate.
• r_{max}: Intrinsic per capita rate of increase (or population growth), estimated as r (birth rate - death rate).
• K: Carrying capacity.

Life-History Continuum

• Low fecundity:
  • High survivorship.
  • Few offspring.
  • Large offspring.
  • Late maturity.
  • Large body size.
  • High disease resistance.
  • High predator resistance.
  • Long life span.
• High fecundity:
  • Low survivorship.
  • Many offspring.
  • Small offspring.
  • Early maturity.
  • Small body size.
  • Low disease resistance.
  • Low predator resistance.
  • Short life span.

Population Size and r Values

• Population size is denoted as N.
• Examples of r values:
  • Bacterium E. coli: 59 (High r).
  • Ciliate P. caudatum: 1.6 (Moderate r).
  • Flour beetle: 0.10 (Low r).
  • Domestic cow: 0.001 (Very low r).
  • Beech tree: 0.000075 (Very low r).

Density Dependence

• Growth rate slows at high density.
• Logistic growth in ciliates:
  • Early growth is rapid.
  • Growth begins to slow.
  • Later growth falls to zero.

Equations for Population Growth

• \frac{dN}{dt} = r_{max}N
• \frac{dN}{dt} = r_{max}N \frac{K - N}{K}
• \frac{dN}{dt} = r_{max}N (1 - \frac{N}{K})
  • This equation accounts for the carrying capacity (K) in the growth equation.

Density-Dependent Factors

• Survival of gobies declines at high population density.
• Fecundity of sparrows declines at high population density.
• Reindeer introduced to St. Paul Island (Alaska) as an example.

Density-Dependent Factors That Limit Population Size

• Competition for resources:
  • Food
  • Territory
  • Water
  • Light
  • Nesting sites
  • Nutrients
  • Oxygen
• Disease and parasitism:
  • Stress-related degradation of health.
  • Infectious disease.
  • Parasitism.
• Predation: Increased predation as prey density increases.
• Toxic wastes:
  • Ammonia
  • Uric acid
  • Alcohol
  • Carbon dioxide
• Social behavior:
  • Stress-mediated behavior.
  • Dominance behavior.
  • Mating behavior.
  • Parental-care behavior.
  • Predator-avoidance behavior.

Hare-Lynx Population Cycle

• The hare-lynx populations cycle every 10 years, on average; changes in lynx density lag behind changes in hare density.
• Research question: What factors control the hare-lynx population cycle?
• Hypotheses:
  • Bottom-up hypothesis: Food availability for the hares controls the hare-lynx cycle.
  • Top-down hypothesis: Predation controls the hare-lynx cycle.
  • Interaction hypothesis: The interaction of food availability and predation controls the hare-lynx cycle.
  • Null hypothesis: The hare-lynx cycle isn't driven by predation, food availability, or a combination of those two factors.
• Experimental setup: Document hare population in seven study plots from 1987 to 1994.
• Conclusion: Hare populations are limited by both predation and food availability. When predation and food limitation occur together, they have a greater effect than either factor does independently.

Human Population Growth

• World population growth through history.
• Significant milestones: Old Stone Age, New Stone Age, Bronze Age, Iron Age, Middle Ages, and Modern Age.
• Noteworthy events: Black Death (the plague).
• Population milestones: 0.3 billion in 1 A.D., rapid growth in recent centuries.
• The years in which the population hit specific billions: 1804 (1 billion), 1927 (2 billion), 1960 (3 billion), 1974 (4 billion), 1987 (5 billion), 1999 (6 billion), 2011 (7 billion).

Demographic Transition Model (DTM)

• Explains population changes over time.
• Stages:
  • Stage 1: High birth and death rates.
  • Stage 2: Death rate declines, birth rate remains high.
  • Stage 3: Birth rate declines.
  • Stage 4: Low birth and death rates.
• Based on demographic change in Sweden from 1735-2000.

World Population Growth Rate

• World population growth rate slows, which might seem like good news, but even if birth rates dropped to simple replacement of parents, the world’s population would still grow due to age structure.

Age Structures and Sex Ratios

• Age structures (and sex ratios) differ between developed (e.g., Sweden) and developing (e.g., Honduras) countries.
• Population pyramids show the distribution of males and females across different age groups.

Demographic Transition Model Considerations

• Provides important insight but disregards migrations and is based on the history of European countries.

Human Population Size Peak

• The UN has projected human population growth to the year 2050 based on current fertility rates.
• Scenarios include:
  • High: 2.5 children per woman
  • Medium: 2.1 children per woman
  • Low: 1.7 children per woman
• Zero population growth (ZPG) results when fertility at the replacement rate is sustained for a generation.
• The future of the human population hinges on fertility rates--on how many children each woman living today decides (or is allowed to decide) to have.

UN Projection by Region

• The world’s population will still be on the rise.
• Using a log scale.

Human Carrying Capacity

• Discussion on human carrying capacity.

Community Ecology 1

• Introduction to Community Ecology.

Food Web

• Components:
  • Decomposers: Bacteria/crustations
  • Insects
  • Primary Consumers: Herbivores, omnivores, small animals
  • Secondary Consumers: Reptiles, rodents, small herbivores
  • High Level Consumers: Mammals, carnivores, large animals

Species Interactions

• Types of Interactions:
  • Competition (-/-)
  • Amensalism (0/-)
  • Exploitation (+/-)
  • Neutral (0/0)
  • Commensalism (+/0)
  • Mutualism (+/+)
• Interaction forms are not necessarily "settled" forever; populations evolve!

Commensalism Example

• Epiphytic orchid on a tree host.

Competition

• Competition is a -/- interaction that lowers the fitness of the individuals involved.
• Intraspecific competition: Between members of the same species -> density-dependent population growth.
• Interspecific competition: Members of different species use the same limiting resources.

Intraspecific Competition and Density Dependence

• Intra-specific competition -> density dependence
• Growth rate slows at high density.
• Logistic growth in ciliates.
• \frac{dN}{dt} = r_{max}N(1 - \frac{N}{K})

Competitive Exclusion Principle

• Competing species cannot coexist in laboratory experiments.
• Mathematical models predict that one species drives the other to extinction.
• Two species using the same resources cannot coexist.
• Assumptions:
  • Competition is “complete” (competitors have exactly the same resource requirements).
  • Environmental conditions constant.

Niche Differentiation

• Difference between fundamental and realized niche.

Semibalanus Removal Experiment

• The question is about valid conclusions from the Semibalanus removal experiment.

Competition Along Environmental Gradients

• Examples with Alpine, Lodgepole pine, Yellow pine, and Least chipmunks.

Niche Differentiation and Natural Selection

• Natural selection selects against individuals that compete.

Character Displacement

• Evolutionary change in traits that reduces the amount of niche overlap and the amount of competition.

How do Species Coexist?

• Resource partitioning.
• Over ecological time:
  • Realized niches.
  • Combined effects of resource use and environmental requirements/tolerances + the actual environmental conditions (variable!) determine competitiveness.
• Over evolutionary time:
  • If natural selection favors resource use at different ends of the range: Character displacement.