Population Ecology Quiz

Species Distribution & Abundance

• Species distribution patterns include random, regular, and clumped, influenced by interactions among individuals and scale.
• Mapping distributions shows species ranges, but not individual locations.
• Understanding these patterns is key for conservation and ecological studies.
• Random distribution: equal chance of being found anywhere, often due to neutral interactions.
• Regular distribution: individuals avoid each other or claim exclusive areas (territorial species).
• Clumped distribution: mutual attraction or limited dispersal (common in social species).
• Species rarity is linked to population size, range, and habitat tolerance, affecting extinction risk.
• Rare species are vulnerable to extinction due to limited range and habitat needs, especially impacted by human actions.

Population Structure

• Population structure includes mortality, age distributions, sex ratios, and dispersal patterns, defining population dynamics.

• Factors like birth/death rates, immigration/emigration influence population size and structure (∆P = BR – DR + IR - ER).

• Understanding population demographics is crucial for assessing population health and predicting future trends.

• Life tables summarize survival patterns (age-specific survival/mortality).

• Types of life tables include: cohort (individuals born at the same time), static (snapshot survival), and age distribution analysis.

• Age distribution reflects the proportion of individuals in different ages, vital for understanding population dynamics and predicting growth/decline, essential for conservation.

• Survivorship curves:

  • Type I: high survivorship throughout life (e.g., humans).
  • Type II: constant survivorship regardless of age (e.g., some birds).
  • Type III: low survivorship in early life, higher at maturity (e.g., many fish).

• Age distribution analysis reveals historical survival/reproduction patterns, indicating future growth. Identifies successful reproduction periods and survival rates for juveniles and adults. Reveals if older individuals are being replaced by younger ones.

• Case studies:

  • White Oak: stable population, sufficient reproduction.
  • Rio Grande Cottonwoods: declining due to reduced seasonal floods affecting seedlings.

Population Dynamics and Growth Models

• Density-dependent and density-independent factors affect population size (e.g., birth/death rates, immigration/emigration).
• Geometric growth occurs in populations with pulsed reproduction (non-overlapping generations). Formula: 𝑁𝑡 = 𝑁0𝜆𝑡.
• Exponential growth occurs in populations with overlapping generations, growth proportional to current size. Formula: 𝑑𝑁/𝑑𝑡 = 𝑟𝑁.
• Logistic growth: resources limit growth, slowing as population approaches carrying capacity (K). Curve is sigmoidal (S-shaped).

Competition in Ecology

• Competition occurs when individuals (same or different species) compete for resources. Competition can be categorized as:

  • Competition (-/-): individuals compete for the same resources.
  • Exploitation (+/-): one species benefits at expense of another.
  • Mutualism (+/+): both species benefit.
  • Commensalism (+/0): one species benefits, the other is unaffected.

• Intraspecific competition: among individuals of the same species (often leading to self-thinning).

• Interspecific competition: between individuals of different species.

• Mechanisms include interference (direct, aggressive interactions like territorial disputes) and exploitative (indirect competition for resources).

• Competitive Exclusion Principle: two species with identical niches cannot coexist indefinitely.

• Intraspecific competition formula: 𝑑𝑁/𝑑𝑡 = 𝑟_{max} 𝑁 (1 - 𝑁/𝐾). (rmax=max growth rate, N= pop size, K=carrying capacity)

• Interspecific competition involves competition coefficient (α), affecting the growth rates when different species are competing for the same resources. (α12 example, for species 1's impact on species 2).

• Spatial heterogeneity affects competition strength, allowing coexistence in varied environmental conditions. Factors like food, disease, and predation risk vary spatially. Example: A diverse forest with abundant resources vs. a resource-poor area.

• Competitive equivalence: Similar competitive abilities can lead to unpredictable outcomes; species can win/lose equally over time.

• Niche partitioning: allows coexistence through different resource usage within the same habitat (spatially or temporally), reducing direct competition.

• Competitive abilities (within species) can vary; recognizing this variation is crucial for understanding ecological interactions.

Herbivory and Plant Defense Mechanisms

• Plants use resistance (preventing herbivory) and tolerance (mitigating damage) mechanisms.
• Examples: thorns, spines, and chemical defenses (alkaloids).
• Induced defenses are activated in response to herbivory, while constitutive defenses are always present.
• Overcompensation: increased plant growth after herbivory, often due to nutrient cycling.

Impacts of Predators on Prey Populations

• Predators influence prey populations through consumption and non-consumptive effects (stress, behavioral changes).
• Lotka-Volterra model: Predicts cyclical patterns in predator and prey populations.
• Prey populations use diverse strategies to avoid predation (refugia, defense mechanisms). Includes visual/olfactory displays, behavioral adaptations, and physical refuges.

Mutualism, Parasitism, and Disease

• Disease is defined as an atypical condition causing physiological impairment, influenced by genetic, environmental, and pathogen factors.
• Pathogens are disease-causing organisms, and vectors transmit pathogens.
• Disease population dynamics are influenced by pathogen traits and transmission methods (direct or indirect, horizontal or vertical).

Community Structure and Functioning

• Community structure encompasses species attributes like richness, abundance, and diversity, affecting ecosystem health.

• Ecological function encompasses biological, chemical, and physical processes.

• Species richness and evenness determine species diversity.

• Rank-abundance curves visually represent species relative abundance against rank. Steeper curves indicate fewer dominant species.

• Functional groups consist of organisms with similar ecological roles; understanding them helps predict responses to changes.

• Alpha diversity: diversity within a specific area.

• Beta diversity: differences in species composition between communities.

• Gamma diversity: total diversity within a larger region (synthesis of alpha and beta).

Community Interactions

• Food webs show feeding relationships and illustrate energy/nutrient flow through trophic levels.
• Competitive hierarchies can shape community composition due to superior competitors (indirect influence).
• Keystone species have large impacts on community structure but are often not abundant.
• Ecosystem engineers modify the environment, creating habitats for other species.

Disturbance, Succession, and Stability

• Succession is the gradual change in species composition following disturbance. Types include primary (newly exposed substrates) and secondary (disturbances that don't completely destroy soil).
• Pioneer community: first colonists following disturbance.
• Climax community: stable endpoint of succession.
• Disclimax community: maintained by ongoing disturbances (e.g., grazing).
• Mechanisms of succession include facilitation, inhibition, and tolerance.
• The intermediate disturbance hypothesis: intermediate levels of disturbance can create higher species diversity.
• Community stability: the absence of change due to lack of disturbance. Community resistance (maintaining structure/function despite disturbance) and resilience (recovering after disturbance) are crucial.

Landscape Ecology

• Landscape ecology studies patterns and processes across multiple scales. Landscapes are composed of heterogeneous patches and the matrix surrounding them.
• Landscape structure includes patch size/shape, composition, number, and position.
• Corridors connect similar habitat patches and facilitate species movement.
• Landscape processes are influenced by structure, including energy flow, nutrient cycling, and species distribution across them.
• Edge effects occur at the boundaries of patches.
• Fragmentation impacts species movement and population dynamics.