Ecology and Environment - Organisms and Populations

Ecology Levels: Organisms, Populations, Communities, and Biomes. Ecology at the organismic level is essentially physiological ecology which tries to understand how different organisms are adapted to their environments in terms of survival and reproduction.

Major Abiotic Factors: Temperature, Water, Light, and Soil. Temperature is the most ecologically relevant environmental factor, affecting the kinetics of enzymes and through it the metabolic activity and other physiological functions of the organism.

Responses to Abiotic Factors: Organisms maintain homeostasis through Regulation (constant internal environment), Conformation (internal environment changes with external), Migration (temporary movement to stressful conditions), or Suspension (e.g., Hibernation in bears, Aestivation in snails, and Diapause in zooplankton).

Adaptations: Morphological, physiological, and behavioral attributes that enable organisms to survive and reproduce. Example: Allen's Rule states that mammals from colder climates generally have shorter ears and limbs to minimize heat loss.

Population Attributes: Unlike individuals, populations have attributes like birth rates, death rates, sex ratio, and age distribution (represented by age pyramids: expanding, stable, or declining).

Population Growth: The size of a population ($N$) is determined by Natality ($B$), Mortality ($D$), Immigration ($I$), and Emigration ($E$).

Exponential Growth: Occurs when resources are unlimited. The equation is $\frac{dN}{dt} = rN$, where $r$ is the intrinsic rate of natural increase. The graph is J-shaped.

Logistic Growth: More realistic, as resources are finite. It is described by the Verhulst-Pearl Logistic Growth equation, where population growth levels off at the Carrying Capacity ($K$). The graph is Sigmoid (S-shaped).

Population Interactions: These include Mutualism $(+/+)$, Competition $(-/-)$, Predation $(+/-)$, Parasitism $(+/-)$, Commensalism $(+/0)$, and Amensalism $(-/0)$.