Population and Community Ecology Flashcards

Population Ecology: Fundamentals and Demography

• Population Definition: A population consists of all individuals of a particular species living within the same general area.

• Interbreeding and Gene Pool: The genetic material shared within a population that interbreeds is referred to as the gene pool.

• Demography:     - This is the statistical study of population dynamics.     - It utilizes mathematical tools to investigate how populations respond to changes in their biotic (living) and abiotic (non-living) environments.

• Environmental Effects: The environment can influence various population parameters, including:     - Population density.     - Population distribution (dispersion).     - Age structure.     - Population size.

Population Density and Dispersion

• Population Density: Defined as the number of individuals per unit area or volume.     - Factors Increasing Density: Births and immigration.     - Factors Decreasing Density: Deaths and emigration.

• Population Dispersion: Refers to how individuals within a population are spaced within an area, depending upon environmental and social factors.     - Uniform Distribution: Individuals are evenly spaced. This is often influenced by social interactions such as territoriality. An example is nesting penguins.     - Random Distribution: The position of each individual is independent of others. There are no strong attractions or repulsions between individuals. An example is plants with wind-dispersed seeds (e.g., dandelions).     - Clumped Distribution: The most common pattern, where individuals aggregate in patches. Reasons for clumping include optimal resource availability, protection, social factors, and/or finding mates. Examples include elephants traveling in herds or groups.

Survivorship and Life History Patterns

• Survivorship Curves: These represent the number of survivors at each age for a given species.     - Type I: Low death rates among young and middle-aged individuals, with most deaths occurring among the elderly. Typically seen in humans and other mammals that produce few offspring and provide extensive parental care.     - Type II: Constant death rates throughout the organism's lifespan. Examples include rodents, birds, reptiles, and some invertebrates.     - Type III: High death rates for the young, but the death rate decreases significantly for those who survive past a certain age. Examples include plants, fishes, and some invertebrates that produce many young but provide little or no parental care.

• Life History Traits: An organism's life history describes the series of events over its lifetime, including:     - Age of first reproduction.     - Frequency of reproduction.     - Number of offspring per reproductive effort.     - Life Tables: Data tables describing survivorship and fecundity within a population.     - These traits are genetically determined and shaped by the environment and natural selection.

• Energy Budgets: Living organisms require energy for growth, maintenance, and reproduction. All species have an energy budget where they must balance energy intake with metabolism and parental care.

• Parental Care and Fecundity:     - Fecundity: The potential reproductive capacity of an individual.     - Fecundity is inversely related to parental care.     - Species with many offspring (high fecundity) usually provide little care, using most of their energy budget to produce tiny, self-sufficient (though vulnerable) offspring.     - Species with few offspring provide extensive parental care, often at the expense of the parent's own health, to ensure offspring develop toward self-sufficiency.

• Reproductive Strategies:     - Semelparity: A species reproduces only once in its lifetime and then dies (e.g., Chinook salmon, century plant). Energy is sacrificed for a single massive effort.     - Iteroparity: Species that reproduce repeatedly during their lives (e.g., chimpanzees, pronghorn antelope, most mammals). This is favored in stable environments.

Population Growth Models

• Exponential Growth:     - Occurs when resources are unlimited. Growth becomes more rapid as the population size increases.     - Results in a J-shaped growth curve.     - Example: Bacteria dividing every hour. 1,000 bacteria become 2,000 in one hour, and 16 billion in 24 hours.

• Growth Rate Formulas:     - Per capita rate of change ($r$) equals birth rate minus death rate: $r = \text{birth rate} - \text{death rate}$.     - Change in population size ($N$) over time ($t$):     $\frac{dN}{dt} = rN$     - Biotic Potential: The maximal growth rate for a species ($r_{max}$).

• Logistic Growth:     - Describes reality where limited resources exist.     - Carrying Capacity ($K$): The maximum population size an environment can support.     - Results in a sigmoid (S-shaped) curve.     - Logistic Equation:     $\frac{dN}{dt} = r_{max}N \frac{K - N}{K}$

• Intraspecific Competition: Competition between members of the same species for resources. It intensifies as the population approaches $K$.

• Real-World Variations: Population size may overshoot $K$ for short periods and then fall back, oscillating around the carrying capacity. There may also be a lag time before birth rates decline in response to resource scarcity.

Population Regulation: Biotic and Abiotic Factors

• Density-Independent Factors: Affect all individuals in a population regardless of density. Examples include natural disasters (earthquakes, weather) and long-term drought.

• Density-Dependent Factors: The impact changes as population density varies. Examples include competition for resources, disease, predation, and territoriality.

• K-selected vs. r-selected Species:     - K-selected: Adapted to stable, predictable environments. Exist close to carrying capacity. Traits: late maturation, high longevity, much parental care, few large offspring (e.g., elephants, oak trees).     - r-selected: Adapted to unpredictable environments. Traits: early maturation, short lifespan, little parental care, many small offspring (e.g., dandelions, jellyfish).

Human Population Growth and Impact

• Current Trend: Human population growth since 1,000 AD has been exponential.

• Sustainability: Humans have increased the Earth's carrying capacity through technology, but at the cost of the environment (ozone depletion, acid rain, climate change).

• Demographic Transition: Developed countries often show slower growth (e.g., Europe) while underdeveloped regions (e.g., Asia, Africa) grow faster.

• Overcoming Regulation: Public health, sanitation, and antibiotics have drastically reduced mortality from infectious diseases (e.g., deaths from infectious disease declined from $15.4 \times 10^{6}$ in 1990 to $10.4 \times 10^{6}$ in 2017).

• Age Structure Diagrams:     - Rapid Growth: Pyramidal shape (large base of young individuals).     - Slow Growth: Still pyramidal but with fewer young and reproductive-aged individuals (e.g., US).     - Zero Growth: Bulge in middle-aged and older populations (e.g., Italy).

• Socio-economics: Female education and literacy are directly correlated with lower fertility rates.

• Ecological Footprint:     - A measure of the land/water area required to produce resources and absorb waste per person.     - Sustainable limit: $1.7\,\text{ha}$ per person.     - Average US citizen: $8\,\text{ha}$ per person.

Community Ecology and Species Interactions

• Community Definition: Populations inhabiting a specific area at the same time.

• Species Diversity: Defined by species richness (total number of species) and relative species abundance (proportion of each species).     - Diversity is highest near the equator (warmer, rainier, low seasonality) and lowest at the poles.

• Predation and Herbivory:     - Predator-Prey Cycles: Example of Lynx and Snowshoe Hare. Populations fluctuate in ~10-year cycles, with predators lagging 1–2 years behind prey.     - Defense Mechanisms:         - Mechanical: Thorns (Honey locust), shells (Turtles).         - Chemical: Toxic foxglove plants, millipedes producing noxious substances.         - Camouflage: Tropical walking stick (twig-like), chameleons.         - Aposematic Coloration: Warning colors indicating toxicity or foul taste (e.g., poison dart frog, skunk).

• Mimicry:     - Batesian Mimicry: A harmless species mimics the warning colors of a harmful one (e.g., bee-like robber fly mimicking a bumblebee).     - Müllerian Mimicry: Multiple harmful/unpleasant species share the same warning coloration (e.g., Heliconius butterflies).

• Competitive Exclusion Principle: Two species cannot occupy the same niche. If they compete for all the same resources, one will outcompete the other (demonstrated by Paramecium experiments).

• Symbiosis:     - Commensalism: One benefits, the other is unaffected (+/0) (e.g., birds nesting in trees).     - Mutualism: Both benefit (+/+) (e.g., termites and gut protozoa; corals and zooxanthellae).     - Parasitism: Parasite benefits, host is harmed (+/-) (e.g., tapeworms).

Species Roles and Community Dynamics

• Foundation Species: The "bedrock" of a community, usually primary producers with high abundance (e.g., kelp or coral). They physically modify the environment.

• Keystone Species: A species whose presence is essential to maintaining biodiversity. If removed, the community structure changes drastically.     - Example: Pisaster ochraceus (intertidal sea star). Its removal allows mussel populations to exploded and reduce diversity.     - Example: Banded tetra (fish) that supplies phosphorus to tropical streams.

• Succession:     - Primary Succession: Happens on new land (e.g., lava flows in Hawaii). Pioneer species like lichens and hardy plants break down rock into soil.     - Secondary Succession: Occurs after a disturbance where remnants of the previous community remain (e.g., after a forest fire).         - Sequence: Annual plants → Grasses (pioneer) → Shrubs → Small trees → Climax community (equilibrium state).

Questions & Discussion

• Population Definition: Written in chat as "all individuals of a species living in the same general area."

• Fish Survivorship Scenario: A fish species evolves from a broadcast spawner (Type III) to a mouth brooder (providing care). The expected shift is from Type III to Type I or II because parental care increases survival of the young.

• Seals and Carrying Capacity: If a seal's food source decline due to pollution, both the carrying capacity ($K$) and the seal population size would decrease.

• Roundworm Study: In roundworms, fecundity decreases as population density increases. This is a density-dependent effect.

• Human Population Growth Cause: In the past 300 years, the primary driver has been declining mortality rather than rising fertility.

• Sustainable Consumption: If the sustainable resource limit is $1.7\,\text{ha}$ and Americans use $8\,\text{ha}$, it implies U.S. rates of resource consumption are too high.

• Paramecium Competition: The graph showing P. aurelia thriving while P. caudatum declines in a shared environment illustrates the competitive exclusion principle.

• Rapid Growth Prediction: Regions with a pyramidal age structure (wide base) are expected to increase in population most quickly because of the massive number of individuals entering reproductive years.