Introduction to Ecology: Scales, Factors, and Biomes

Introduction to Ecology

Definition and Scope

Ecology is the scientific study of the interactions between organisms and their environment, which determine the distribution (where organisms are found) and abundance (how many there are) of organisms. These interactions can be with both living (biotic) and nonliving (abiotic) components of the environment.

• Biotic factors: Interactions among living organisms (e.g., competition, predation, mutualism).

• Abiotic factors: Nonliving environmental components (e.g., climate, soil, water, temperature).

Example: The distribution of Alligator mississippiensis is determined by both the availability of suitable wetland habitats (abiotic) and interactions with other species (biotic).

Ecological Scales

Levels of Ecological Study

Ecology can be studied at multiple hierarchical levels, each focusing on different aspects of biological organization:

• Organismal Ecology: Examines how individual organisms adapt physiologically and behaviorally to their environment.

  • Physiological ecology: How organisms' bodies function in response to environmental conditions.

  • Behavioral ecology: How behaviors contribute to survival and reproductive success.

• Population Ecology: Focuses on groups of interbreeding individuals (populations), studying factors affecting population growth, density, and size.

• Community Ecology: Investigates how populations of different species interact and form functional communities. Explores why some areas are species-rich and others are species-poor.

• Ecosystem Ecology: Studies the flow of energy and cycling of elements (e.g., carbon, nitrogen) among organisms and their environment.

• Landscape Ecology: Examines spatial patterns and how they affect ecological processes across larger areas.

• Global Ecology: Considers ecological phenomena at the biosphere level, including global patterns and processes.

Additional info: These scales are interconnected; processes at one level can influence others.

Abiotic and Biotic Factors Affecting Distribution and Abundance

Abiotic Factors

Abiotic factors are nonliving components that influence where organisms can live and how abundant they are.

• Temperature: Affects biological processes such as cellular respiration, enzymatic activity, and the ability to survive freezing or heat stress.

• Wind: Influences heat loss (evaporation, transpiration, convection), ocean circulation, and wave action.

• Water Availability: Essential for all life; influences plant and animal distribution. Swamp plants thrive in flooded conditions, while sand dune plants are adapted to dry environments.

• Oxygen Levels: Especially important in aquatic systems; low oxygen can limit species presence.

• Light Levels: Determines where photosynthesis can occur, especially in aquatic systems (limited to the top ~100m).

• Salinity: Affects osmoregulation in aquatic organisms; marine fish must compensate for water loss in hypertonic environments.

• pH: Most terrestrial and aquatic organisms can only tolerate a narrow pH range. Acidic conditions can inhibit key biological processes.

• Rocks and Soils: Influence nutrient availability and plant growth.

• Nutrient Levels: Limit productivity in both terrestrial and aquatic ecosystems.

Biotic Factors

Biotic factors are interactions among living organisms that affect distribution and abundance.

• Intraspecific interactions: Interactions within a species (e.g., competition for resources).

• Interspecific interactions: Interactions between different species (e.g., predation, mutualism, competition).

Example: In the Serengeti, grass productivity (affected by rainfall) determines buffalo density, linking plant and animal distributions.

Temperature and Organismal Adaptations

Ectotherms vs. Endotherms

• Ectotherms: Obtain heat from the environment. Most organisms are ectotherms (e.g., fish, reptiles).

• Endotherms: Generate heat through metabolism, allowing survival in colder climates (e.g., mammals, birds). Requires higher energy intake.

Organisms experience stress and may not survive outside their optimal temperature range. For example, corals bleach at high temperatures due to the loss of symbiotic algae.

Climate Change and Species Distribution

Global Warming Effects

• Atmospheric CO2 has been increasing, leading to a warming climate.

• Climatic zones may shift faster than some species (e.g., trees) can migrate, potentially leading to range contractions or extinctions.

• Water temperatures may rise faster than coral populations can adapt, causing widespread coral bleaching.

Rate of warming is a critical factor in determining whether species can adapt or migrate quickly enough to survive.

Other Abiotic Factors

Wind

• Amplifies temperature effects by increasing heat loss (wind chill).

• Drives ocean circulation and wave action, influencing nutrient distribution and marine life.

Salinity

• Marine fish in hypertonic environments lose water and must drink seawater, excreting excess salt via gills and kidneys.

• In terrestrial systems, salt can accumulate in arid areas due to evaporation. Halophytes are plants adapted to high-salt environments, often with specialized salt glands.

pH

• Normal rainwater pH is about 5.6; most plants grow best at pH 6.5.

• pH below 5.2 inhibits nitrifying bacteria, affecting nutrient cycling.

• Freshwater and marine organisms are also sensitive to pH changes; ocean acidification (from increased CO2) reduces pH and impacts organisms with calcareous shells.

Water and Nutrient Availability

• Water availability shapes plant and animal distributions. Deep roots help plants survive in dry environments.

• Photosynthesis in aquatic systems is limited to the photic zone (~100m depth), with different algae adapted to varying light wavelengths.

• Nutrient availability is a key factor in marine productivity and species distribution.

Terrestrial and Aquatic Biomes

Classification of Biomes

Terrestrial biomes are classified primarily by mean annual precipitation and temperature, which together define the climate. Patterns of rainfall are largely driven by global air circulation, which is influenced by uneven heating of the Earth and its rotation.

• Hadley cell: A large-scale atmospheric convection cell in which air rises at the equator and sinks at medium latitudes, driving tropical rainfall patterns.

• Elevation and latitude both affect climate and biome distribution; higher elevations and latitudes are generally cooler.

• Rain shadow effect: Mountains block moist air, causing precipitation on the windward side and dry conditions on the leeward side.

Aquatic biomes are classified based on light penetration (photic vs. aphotic zones), proximity to the bottom (benthic vs. pelagic), and nutrient availability.

Barriers to Dispersal and Biogeography

Geographic Barriers

• Physical barriers (e.g., mountains, oceans, landmasses) limit the ranges of species.

• Continental drift and the movement of landmasses over geologic time have shaped current biogeographic patterns.

• Boundaries of biogeographic provinces reflect historical and current barriers to dispersal.

Example: The yellow-bellied sea snake cannot expand its range from the eastern Pacific to the Caribbean due to the land barrier of Central America.

Key Terms and Definitions

• Ecology: Study of interactions between organisms and their environment.

• Climate: Prevailing weather patterns in a region over long periods.

• Biome: Major ecological community type defined by climate and dominant vegetation.

• Biotic: Living components of an ecosystem.

• Abiotic: Nonliving components of an ecosystem.

• Ectotherm: Organism that relies on external sources of heat.

• Endotherm: Organism that generates heat metabolically.

• Species range: Geographic area where a species is found.

• Species distribution: Pattern of where species are located within their range.

• Hadley cell: Large-scale atmospheric circulation pattern responsible for tropical rainfall and desert formation.

Summary Table: Major Abiotic Factors and Their Effects

Abiotic Factor	Effect on Organisms	Example
Temperature	Regulates metabolic rates, survival, and reproduction	Coral bleaching at high temperatures
Water Availability	Limits plant growth and animal distribution	Swamp vs. sand dune plants
Salinity	Affects osmoregulation in aquatic organisms	Marine fish excrete salt at gills
pH	Influences nutrient cycling and organism survival	Acid rain inhibits nitrifying bacteria
Light	Limits photosynthesis in aquatic systems	Algae with different pigments at various depths
Nutrients	Limits productivity and species richness	Low nutrients limit marine phytoplankton