Immigration, Population Dynamics and Species Interactions in Ecology

Immigration and Population Measurements

• Immigration refers to moving to a specific country from another.
• Population measurements focus on individuals moving between countries.

Replacement Level Fertility Rate

• The replacement level fertility rate is the average number of children a couple must have to replace themselves, typically between 2.1 and 2.5.
  • Explanation:
  • You might think it should just be 2 (for two parents), but this number accounts for mortality rates where not all children survive to reproduce.

Total Fertility Rate (TFR)

• A visual map shows the TFR (the average number of children born to a woman over her lifetime).
• Higher fertility rates are often linked to higher population growth.
  • Example: Countries are colored indicating their fertility rates; darker colors (purple to red) denote higher for TFR.
• Contrastingly, some countries, like Russia, have stable or decreasing fertility rates, indicating fewer births than needed to maintain the current population size.

Factors Influencing Fertility Rates

• Education leads to delayed marriage and parenthood, resulting in fewer children per family.
• Disparities in healthcare access and health outcomes affect different racial groups in the USA, impacting population metrics.

Age Distribution in Populations

• Population structure can be visualized:
  • A triangular bar chart shows the number of individuals per age group.
  • Countries with a wide base (many young individuals) indicate potential future population growth.
  • Conversely, a narrowing base suggests a declining population due to fewer young people.

Population Growth Rates

• Population growth can be influenced by density-dependent effects, where increasing population leads to competition for resources.
• As population approaches carrying capacity, growth rates slow down due to:
  • Increased competition
  • Higher chances of disease spread.
• Competition Types:
  • Intraspecific Competition: Competition among individuals of the same species.
  • Interspecific Competition: Competition among different species for similar resources.

Ecological Interactions

• Key terms include:
  • Niche: The role or function of an organism in its ecosystem, encompassing resources, habitat, and interactions.
  • Fundamental Niche: The potential environment an organism can occupy.
  • Realized Niche: The actual environment occupied, considering competition and resource availability.

Competitive Exclusion Principle

• This principle states that two species competing for the exact same resources cannot coexist; one will always outcompete the other.
  • Example: Gause's Paramecium Experiment demonstrated competitive exclusion when P. caudatum was driven to extinction by P. aurelia in shared environments.

Case Studies on Competition and Coexistence

• Barnacle Study: Investigated niche differentiation between two barnacle species based on tidal zones.
  • Removal experiments showed the realized niche of a species is affected heavily by competition.
• Darwin's Finches: Demonstrated how two similar species evolved different traits (beak depth) when living in close proximity, adapting to different food sources.

Predation and Herbivory

• Predation: Positive-negative interactions where predators benefit and prey are harmed.
  • It’s crucial in controlling prey populations and maintaining ecosystem balance.
• Herbivory: Although it's a consumption interaction, herbivores usually do not kill plants completely.
• Plant Defenses Against Herbivory:
  • Physical defenses (spines, toxins).
  • Example: Milkweed produces toxic compounds that deter most herbivores, but some, like monarch caterpillars, have adapted and can store these toxins to deter their own predators.

Mimicry in Ecology

• Mimicry Types:
  • Batesian Mimicry: A harmless species mimics a harmful species to avoid predation.
  • Müllerian Mimicry: Two harmful species evolve to resemble each other, benefiting both through shared avoidance by predators.

Conclusion

• The interactions among species, their reproductive strategies, population dynamics, and ecological adaptations play critical roles in shaping ecosystems. The knowledge of these dynamics is vital for understanding ecological stability and species coexistence.