BIO105: Intro to Ecology and Biomes Study Notes
Introduction to Ecology and Biomes
Core Concepts and Vocabulary
Biome: A large naturally occurring community of flora and fauna occupying a major habitat, e.g., forest or tundra. Biomes are characterized by their climate, dominant plant forms, and associated animal life.
Windward and Leeward Sides of Mountains:
Windward Side: The side of a mountain range that faces the prevailing wind. Air is forced upward, cools, and condenses, leading to high precipitation.
Leeward Side: The side of a mountain range that is sheltered from the wind. Descending air warms and dries, often creating a rain shadow desert and significantly lower precipitation.
Hadley Cell: A large-scale atmospheric convection cell in the Earth's atmosphere that transports heat from the equator to about (30^{\circ}) latitude in both hemispheres. Warm, moist air rises at the equator, cools, precipitates, and then descends as dry air at (30^{\circ}) latitude, influencing global climate patterns and biome distribution.
Photic vs. Aphotic Zone: These terms describe light penetration in aquatic environments.
Photic Zone: The upper layer of a body of water (ocean or lake) where sunlight penetrates sufficiently for photosynthesis to occur.
Aphotic Zone: The deeper layer of a body of water where little to no sunlight penetrates, meaning photosynthesis cannot occur.
Benthic: Pertaining to the bottom or seabed of a body of water (oceans, lakes, or rivers). Organisms living in this zone are called benthos.
Estuary: A partially enclosed coastal body of brackish water where freshwater from rivers or streams mixes with saltwater from the ocean. They are highly productive and vital nurseries for many aquatic species.
Productivity (Annual Net Primary Productivity – ANPP):
Productivity: The rate at which an ecosystem's producers (primarily plants) convert solar energy into chemical energy (biomass).
Annual Net Primary Productivity (ANPP): The total amount of biomass produced by primary producers in an ecosystem over a year, minus the amount used by the producers for their own respiration. It represents the energy available to higher trophic levels.
Oligotrophic and Eutrophic: Terms describing the nutrient status and productivity of aquatic ecosystems.
Oligotrophic: Characterized by low nutrient levels, clear water, and often high oxygen concentrations in the bottom waters. These lakes typically have low primary productivity.
Eutrophic: Characterized by high nutrient levels, often turbid water due to high algal growth, and potentially low oxygen (hypoxia or anoxia) in deeper waters due to decomposition. These lakes have high primary productivity.
Thermocline and Turnover (of Lakes):
Thermocline: A distinct layer within a large body of water where temperature changes more rapidly with depth than it does in the layers above or below. It separates warmer surface waters from colder deep waters.
Turnover: The seasonal mixing of water layers in temperate lakes, typically occurring in spring and fall. This process breaks down stratification, redistributes oxygen from the surface to deeper waters, and brings nutrients from the bottom to the surface, crucial for lake ecosystem health.
Biome Classification and Influencing Factors
There are numerous ways to classify biomes due to the significant diversity that exists even within broadly defined biome categories. For example, a temperate deciduous forest can show substantial variation, with some areas dominated by oak and hickory, others by beech and ash, and still others by maples.
Factors Accounting for Intrabime Differences:
Microclimate Variations: Subtle differences in local temperature, precipitation, humidity, and sunlight exposure due to topography, elevation, or proximity to water bodies.
Soil Composition: Variations in nutrient content, pH, drainage, and soil texture can favor different plant species.
Historical Factors: Past disturbances (e.g., fires, logging, glaciation), migration patterns, and evolutionary history can lead to regional differences in dominant species.
Disturbance Regimes: The frequency and intensity of natural disturbances (e.g., wildfires, floods, insect outbreaks) can shape the plant community.
Species Interactions: Competition, herbivory, and disease can also influence which species thrive in a particular location.
Understanding Climate Graphs
Climate graphs plot monthly average temperature and precipitation for a specific location. It's crucial to understand that in these graphs, the X and Y axes (typically months on X, temperature and precipitation on Y) are not explanatory and response variables in the traditional sense. Instead, the shapes and patterns within the figure (e.g., lines for temperature, bars for precipitation) are the responses to the monthly timeline shown on the X-axis and the values on the Y-axis.
Absence of Cold and Wet Terrestrial Biomes
There are essentially no terrestrial biomes that are both consistently very cold and receive abundant liquid precipitation. This is primarily because when temperatures are consistently cold (below (0^{\circ}C)), precipitation falls as snow or ice, rather than liquid rain. This frozen water is often locked up in glaciers or permafrost, making it unavailable to plants in liquid form for much of the year, despite potentially high accumulation. Areas like polar deserts are cold, but also dry.
Factors Influencing Terrestrial Temperature and Precipitation
Multiple factors interact to determine the climate of a terrestrial location:
Latitude: Influences solar radiation intensity and duration, leading to warmer temperatures near the equator and colder temperatures near the poles. It also drives large-scale atmospheric circulation (like the Hadley Cells).
Altitude (Elevation): Higher elevations generally experience lower temperatures and often higher precipitation (orographic lift).
Proximity to Oceans/Large Water Bodies: Oceans moderate temperatures, keeping coastal areas warmer in winter and cooler in summer. They also provide a source of moisture for precipitation.
Ocean Currents: Can transport warm or cold water across vast distances, significantly influencing coastal climates (e.g., the Gulf Stream warms parts of Europe).
Atmospheric Circulation: Global wind patterns, including the Hadley, Ferrel, and Polar Cells, distribute heat and moisture, creating distinct bands of high and low pressure, which correspond to arid or wet regions.
Mountain Ranges: Act as barriers to air masses. The windward side receives high precipitation, while the leeward side experiences a rain shadow, leading to dryness.
Other Factors Influencing Biome Existence
Beyond just temperature and precipitation, several other crucial factors shape the specific biome found in a location:
Soil Type: Dictates nutrient availability, water retention, and aeration, which are critical for plant growth.
Disturbance Regimes: Natural events like fire, floods, droughts, and insect outbreaks can prevent climax communities from forming and favor species adapted to these disturbances.
Topography: Slope, aspect (direction a slope faces), and elevation influence microclimates and water availability.
Geological History: Past glaciations, volcanic activity, and continental drift have shaped current landscapes and species distributions.
Human Impact: Land use change, pollution, and climate alteration significantly modify natural biome patterns.
Seasonality and Adaptations in Temperate Biomes
We reside in a temperate deciduous forest biome, characterized by distinct seasons. Temperateness refers to these seasonal temperature changes.
Cause of Seasons
Seasons are caused by the tilt of Earth's axis at approximately 23.5^{\circ} relative to its orbital plane around the Sun. As Earth orbits the Sun, different hemispheres are tilted towards or away from the Sun at various times of the year. When a hemisphere is tilted towards the Sun, it receives more direct sunlight and experiences longer days, leading to summer. When titled away, it receives less direct sunlight and shorter days, leading to winter.
Challenges Presented by Seasons
Seasons present significant challenges for plants and animals:
Plants:
Winter: Low temperatures cause water to freeze (unavailable liquid water), reduced sunlight for photosynthesis, and increased risk of frost damage.
Summer: Can bring heat stress and drought in some regions.
Animals:
Winter: Scarcity of food or water, extreme cold, reduced daylight for foraging.
Summer: Increased competition, potential for overheating.
Adaptations to Seasonality
Organisms in temperate regions have evolved diverse adaptations to cope with seasonal changes:
Plants:
Deciduousness: Shedding leaves in autumn to conserve water during cold, dry winters and reduce metabolic activity (e.g., maple, oak trees).
Dormancy/Seed Banks: Entering a dormant state or surviving as seeds through adverse conditions.
Evergreen Conifers: Adapting to cold with needle-like leaves, thick waxy cuticles, and antifreeze compounds.
Animals:
Migration: Moving to warmer climates or areas with more abundant food resources (e.g., many bird species).
Hibernation/Torpor: Entering a state of reduced metabolic activity, lower body temperature, and slowed heart rate to conserve energy during winter (e.g., bears, groundhogs).
Physiological Adaptations: Growing thicker fur or feathers, changing coat color for camouflage (e.g., snowshoe hare), storing fat reserves.
Behavioral Adaptations: Food caching, seeking shelter (burrows, dens), social huddling.
Marine Biomes: Productivity and Zones
Despite Earth being the "Blue Planet," much of its water is saline and unusable for humans without extensive and costly filtration. Furthermore, large expanses of the ocean are often referred to as "deserts" due to very low productivity.
Factors Increasing Ocean Productivity
Ocean productivity, referring to the rate of photosynthesis by phytoplankton, is primarily limited by light and nutrient availability. Factors that increase productivity include:
Nutrient Availability:
Upwelling: The process where deep, cold, nutrient-rich water rises to the surface, bringing essential nitrates, phosphates, and silicates that fuel phytoplankton growth. This is common along coastlines and in equatorial regions.
River Runoff: Rivers carry terrestrial nutrients (e.g., nitrogen, phosphorus) into coastal waters, enhancing productivity in estuaries and nearshore areas.
Oceanic Fronts: Where different water masses meet, causing turbulence and nutrient mixing.
Sunlight (Photic Zone): Productivity is highest in the photic zone, the upper layer where sufficient light penetrates for photosynthesis. Any factor that increases light penetration (e.g., clear water) or keeps phytoplankton in the photic zone can enhance productivity.
Mixing and Stratification: While stable stratification (warm water over cold) prevents nutrient mixing, occasional mixing events (e.g., storms, seasonal changes in temperate zones) can bring nutrients to the surface, boosting productivity. However, prolonged turbulent mixing can push phytoplankton below the photic zone, reducing productivity.
Iron Fertilization: In some high-nutrient, low-chlorophyll (HNLC) regions, the limiting factor is iron. Introduction of iron can significantly increase phytoplankton blooms.
Freshwater Biomes: Streams, Lakes, and Productivity
Freshwater lakes and streams constitute a very small percentage of Earth's total water, with a significant amount of surface freshwater residing in the Great Lakes. Despite their small volume, streams are remarkably diverse, hosting nearly half of all fish species on Earth, either exclusively or for a portion of their lives.
High Diversity in Streams Compared to Oceans
The high biodiversity in streams, especially fish diversity, compared to the vast oceans can be attributed to several factors:
Habitat Heterogeneity: Streams exhibit tremendous variation over short distances. They have diverse microhabitats, including riffles (fast, shallow, turbulent water), pools (slow, deep water), runs (moderate flow), undercut banks, woody debris, and diverse substrate types (rocks, gravel, sand, mud). This variety creates niches for many specialized species.
Interaction with Terrestrial Environment (Allotrophy): Streams are intimately connected to their surrounding terrestrial landscape. They receive significant inputs of organic matter, sediments, and nutrients from land (e.g., fallen leaves, insects). This allochthonous input of resources provides a broader base for the food web.
Longitudinal Zonation: As streams flow from their headwaters to larger rivers, there are gradual changes in physical conditions (e.g., width, depth, temperature, substrate, flow regime, oxygen) that lead to distinct communities and species distributions along their length.
Flow Dynamics: The constant flow, while challenging, also creates distinct habitats and transports resources, contributing to unique adaptations and species assemblages.
Barriers and Isolation: Unlike the interconnected oceans, stream systems are often isolated by landmasses, waterfalls, or drainage divides. This isolation promotes allopatric speciation over evolutionary time, leading to a high degree of endemism and diversification of fish species in different river basins.
Variability: Streams experience more rapid and localized changes in environmental conditions (e.g., temperature flux, flood events, drought) than the open ocean, driving adaptive radiation.
Eutrophication and its Impacts
Eutrophication is the natural process where a body of water gradually becomes richer in nutrients over time. While a slow natural process, human activities have accelerated it dramatically, leading to what is termed cultural eutrophication.
Cultural Eutrophication
Cultural eutrophication refers to the rapid enrichment of aquatic ecosystems with nutrients, primarily nitrogen and phosphorus, due to human activities such as:
Agricultural runoff (fertilizers, livestock waste).
Sewage discharge (untreated or poorly treated wastewater).
Industrial effluents (containing nutrients).
Urban runoff (detergents, pet waste).
Atmospheric deposition of nitrogen compounds.
Issues Associated with Cultural Eutrophication
The consequences of cultural eutrophication are severe and include:
Algal Blooms: Excessive nutrient input leads to rapid, uncontrolled growth of algae and cyanobacteria (blue-green algae), forming dense "blooms" on the water surface. These blooms block sunlight from reaching submerged aquatic vegetation.
Light Deprivation: The dense algal layer reduces light penetration to the benthic zone and lower depths of the photic zone, killing off submerged plants that are vital for habitat and oxygen production.
Hypoxia and Anoxia (Dead Zones): When the dense algal blooms die, they sink to the bottom. Decomposers (bacteria) consume the dead organic matter, using up large amounts of dissolved oxygen in the process. This leads to hypoxic (low oxygen) or anoxic (no oxygen) conditions in deeper waters, creating "dead zones" where most fish and other aquatic life cannot survive.
Loss of Biodiversity: Fish kills, elimination of oxygen-sensitive invertebrates, and the disappearance of native plant species reduce the overall biodiversity of the affected ecosystem.
Toxic Algae (Harmful Algal Blooms - HABs): Some types of cyanobacteria produce toxins (e.g., microcystins, saxitoxins) that can be harmful or fatal to fish, other aquatic animals, pets, livestock, and humans who consume contaminated water or shellfish.
Taste and Odor Problems: Algal blooms can impart unpleasant tastes and odors to drinking water, requiring additional treatment.
Economic Impacts: Harmful algal blooms can disrupt fisheries, impact tourism (unsuitable for swimming or boating), and increase water treatment costs.
Habitat Degradation: The accumulation of dead organic matter can alter the physical structure of the benthic environment, further degrading habitats for bottom-dwelling organisms.