Ecology
1. Populations
Population Size, Density, Dispersion:
Population Size: Refers to the total number of individuals within a defined area (population size can change due to factors such as birth rates, death rates, immigration, and emigration).
Density: The number of individuals per unit area or volume, which can significantly affect interactions among organisms.
Calculation: Density can be calculated using the formula: .
Dispersion: The manner in which individuals are spaced within a given area. There are three main types:
Clumped: Individuals are grouped in patches (e.g., herds of elephants).
Uniform: Individuals are evenly spaced due to territorial behavior (e.g., king penguins).
Random: Individuals are distributed without a predictable pattern (e.g., dandelions in a field).
Population Growth Models:
Exponential Growth:
Characterized by rapid increase in population size when resources are unlimited. Represented by the equation , where variables represent initial population size, growth rate, and time respectively.
Examples: Bacterial populations multiplying in favorable environments.
Logistic Growth:
Describes how a population’s growth rate decreases as it approaches the carrying capacity (K), resulting in an S-shaped curve. The equation to model this is .
Examples: Deer populations in a forest when food resources are limited.
Life History Strategies:
r-strategists:
Species that reproduce quickly, producing a high number of offspring with minimal parental care (e.g., insects like cockroaches or weeds). R-strategists thrive in unpredictable environments where opportunism is advantageous.
K-strategists:
Species that provide extensive parental care and invest in fewer offspring (e.g., elephants, humans). K-strategists tend to stabilize at or near carrying capacity in specific habitats.
Survivorship Curves:
Type I: Characterized by low mortality in early life and high mortality in older age groups (e.g., humans and large mammals).
Type II: Reflects a constant rate of mortality throughout the lifespan (e.g., birds and some reptiles).
Type III: High mortality during early life stages, with those surviving having a higher probability of living long lives (e.g., many fish species).
2. Communities
Species Interactions:
Competition:
Interspecific (between species) and intraspecific (within species) competition can lead to resource partitioning or competitive exclusion.
Example: Two species of birds competing for nesting sites in the same tree.
Predation: Interaction where a predator eats its prey, affecting both populations through dynamics such as the predator-prey cycle (e.g., lynx and snowshoe hare).
Herbivory: When animals consume plants, influencing both plant populations and the herbivore’s own population dynamics (e.g., deer feeding on saplings).
Symbiosis:
Mutualism: Both species benefit (e.g., pollinators like bees and flowering plants).
Commensalism: One species benefits while the other is unaffected (e.g., epiphytic plants growing on trees).
Parasitism: One organism benefits at the expense of another (e.g., tapeworms in mammals).
Keystone Species and Ecosystem Engineers:
Keystone Species: A species that has a disproportionately large effect on its environment relative to its abundance, such as sea otters that control sea urchin populations, maintaining kelp forest health.
Ecosystem Engineers: Organisms that significantly modify their habitat, impacting community structure (e.g., beavers creating wetlands).
Succession:
Primary Succession: Occurs on newly formed or exposed land where soil is not initially present (e.g., colonization of bare rock after a volcanic eruption).
Pioneer Species: Usually lichens and mosses, establish themselves first, creating soil.
Secondary Succession: Occurs in areas where a disturbance has destroyed an existing community but left the soil intact (e.g., after a forest fire, a field will regrow).
Examples: Grasses and wildflowers quickly reestablish before trees return over time.
3. Ecosystems
Energy Flow:
Food Chains and Food Webs:
Food Chains: Linear representation showing who eats whom, while food webs are complex networks depicting all trophic interactions.
Examples: A basic food chain may start with grass (producer) → grasshopper (primary consumer) → frog (secondary consumer) → snake (tertiary consumer).
Trophic Levels:
Producers: Autotrophs that convert sunlight or chemicals into energy (e.g., plants, phytoplankton).
Consumers: Heterotrophs that obtain energy by consuming other organisms (e.g., herbivores, carnivores, omnivores).
Decomposers: Microorganisms that break down dead organic material, recycling nutrients back into the ecosystem (e.g., fungi, bacteria).
Energy Pyramids: Illustrate energy distribution across trophic levels, with only about 10% of energy being transferred to the next level due to energy loss through metabolism and heat.
Biogeochemical Cycles:
Water Cycle: Continuous movement of water through evaporation, condensation, and precipitation, crucial for sustaining life.
Carbon Cycle: Involves the exchange of carbon through photosynthesis, respiration, decomposition, and combustion. This cycle is critical for regulating Earth's climate.
Nitrogen Cycle: Comprises nitrogen fixation, nitrification, assimilation, and denitrification, essential for protein synthesis in living organisms.
Bacteria like Rhizobium in legumes carry out nitrogen fixation.
Phosphorus Cycle: Does not include a gaseous phase, primarily cycling through soil and water, critical for DNA and ATP production. The cycle often limits productivity in ecosystems because phosphorus is less abundant.
4. Behavior and Responses
Innate vs. Learned Behaviors:
Innate Behaviors: Fixed patterns that occur without prior experience, such as migration or reflex actions in animals.
Learned Behaviors: Develop through interaction with the environment, including habituation, classical conditioning, and trial-and-error learning (e.g., birds learning songs).
Taxis and Kinesis:
Taxis: Directional movement towards or away from a stimulus, such as moths moving towards light (positive taxis) or avoidance of light (negative taxis).
Kinesis: Non-directional movement in response to stimulus intensity, such as woodlice moving more vigorously in dry conditions to find moisture.
Communication in Animals: Can occur through vocalizations, body language, pheromones, and chemical signals. Effective communication is crucial for mating, territory establishment, and warning signals.
Cooperative Behaviors and Fitness Advantages:
Behaviors that enhance survival and reproduction in groups, such as pack hunting in wolves, which increases hunting success compared to solitary hunting. Altruistic behaviors, where individuals act to benefit others, can also lead to inclusive fitness.
5. Biodiversity and Conservation
Importance of Biodiversity: Promotes ecosystem stability, resilience against disturbances, and provides resources for humans, including food, medicine, and materials.
Human Impacts:
Habitat Destruction: The leading cause of biodiversity loss, stemming from urban development, deforestation, and agriculture.
Climate Change: Results in shifting ecosystems, affecting species distribution and life cycles.
Invasive Species: Non-native species that disrupt local ecosystems and outcompete native species for resources, leading to declines in biodiversity.
Conservation Strategies:
Strategies include establishing protected areas, restoring ecosystems, and implementing sustainable management practices to preserve both biodiversity and ecosystem functionality. Initiatives may also focus on genetic diversity to provide resilience to species.