Unit 3 - Populations: Specialist vs. Generalist, R/K Selection, and Demographic Transition
Specialist Species: Characterized by a narrow ecological niche, specific food requirements, and smaller ranges of tolerance. They are more prone to extinction and less adaptable, thriving in stable habitats.
Generalist Species: Have a broad niche, high adaptability, and large ranges of tolerance. They are less prone to extinction, more likely to be invasive, and thrive in changing habitats.
K-selected Species ("Quality"): Large with long life spans, slow population growth, few offspring, substantial parental care, and thrive in stable environments with high competition. Typically follow Type I or II survivorship curves.
r-selected Species ("Quantity"): Small with short life spans and high biotic potential. Produce many offspring with minimal parental care and thrive in rapidly changing environments, often becoming invasive. Typically follow Type III survivorship curves.
Carrying Capacity (): The maximum number of individuals an ecosystem can support based on limiting resources.
Overshoot: An event where a population briefly exceeds carrying capacity, leading to resource depletion.
Die-off: A sharp decrease in population following an overshoot, often due to famine or disease.
Population dynamics are influenced by density-dependent factors (food, competition) and density-independent factors (natural disasters).
Growth Rates: Crude Birth Rate (CBR), Crude Death Rate (CDR), and growth rate ( = (CBR - CDR)/10) determine human population dynamics.
Demographic Transition Model: Describes population changes through stages from high birth/death rates to low birth/death rates, leading to stable or declining populations.
Age Structure Diagrams: Show population cohorts (prereproductive, reproductive, post-reproductive) and their implications for growth or decline in human populations.
Questions & Discussion: Specialist species face extinction risk due to narrow diets; r-selected species are often successful invasive species due to high reproductive rates. In cases like the Hudson River, rising invasive species (Zebra Mussels) correlate with declines in native populations (Unionid Mussels).