Ecology and Ecosystems

The study of interactions between organisms and their environment, and how those interactions determine distribution and abundance of organisms.

A community of organisms together with their abiotic environment, linked by energy flow and nutrient cycling.

Structure = the components and their arrangement (species, biomass, soil, canopy layers). Function = the processes (energy flow, nutrient/water cycling, productivity, decomposition).

Abiotic = nonliving factors (light, temperature, water, soil, nutrients). Biotic = living factors (plants, animals, microbes and their interactions).

Abiotic: sunlight, temperature, precipitation, soil texture, wind. Biotic: competition, herbivory, mycorrhizae, decomposers, predators.

Species = group that can interbreed. Population = one species in one area. Community = all populations of different species in an area. Ecosystem = the community plus its abiotic environment and the flows of energy and nutrients.

A community includes only the living organisms. An ecosystem adds the abiotic environment and the energy and nutrient processes.

A gradual change in an abiotic factor across space (e.g., precipitation, temperature, elevation).

West-to-east precipitation decline (rain shadow), elevation (temperature and snowpack), coastal-to-inland (maritime to continental climate), latitude, soil moisture.

Urban-to-rural gradient (impervious surface, heat, pollution), nitrogen deposition, air pollution, forest fragmentation and roads, logging and land-use intensity, light and noise pollution, climate warming.

Weather = short-term atmospheric conditions. Climate = long-term average (typically 30 years) of weather.

Macroclimate (regionallobal), mesoclimate (landscape, e.g., mountains and valleys), microclimate (local, e.g., under a canopy or on a south slope). Different controls dominate at each scale.

Pacific Ocean (moderates temperature, supplies moisture), Cascade and Olympic mountains (orographic lift and rain shadow), prevailing westerly winds, seasonal shift of Pacific pressure systems, mid-latitude position.

Mild, wet winters and warm, dry summers (maritime, Mediterranean-like). Most precipitation falls when light and temperature are lowest.

West: mild temperatures, small seasonal range, high precipitation. East: more extreme temperatures (hotter summers, colder winters), much less precipitation.

Precipitation is high on the coast and windward slopes, then drops sharply in the rain shadow east of the Cascades. Temperature range increases eastward (hotter summers, colder winters).

Moist air is forced up the windward slope, cools, condenses, and drops heavy precipitation. The air then descends the leeward slope, warms and dries, so the back slope is much drier.

Front (windward, west) slope = high precipitation. Back (leeward, east) slope = low precipitation.

The sun's distance barely changes. Air pressure drops with altitude, so rising air expands and cools. The atmosphere is mostly heated from the ground, and thinner air holds less heat (about 6.5 C per km lapse rate).

No. Higher albedo means more sunlight is reflected, so less is absorbed and there is less heating.

The maximum water vapor pressure air can hold at a given temperature. It rises exponentially with temperature.

The difference between saturation vapor pressure and actual vapor pressure. High VPD = dry air, which drives transpiration and causes stomata to close.

Low in winter (cool, low light) and highest in summer (warm, high radiation, high VPD), when soil water supply is lowest.

It is the energy input. Part is reflected (albedo, about 30%) and the rest is absorbed and re-emitted as longwave radiation, so Earth stays in rough balance.

Surplus at low latitudes (tropics, more direct sunlight) and deficit at high latitudes (poles). Heat moves poleward via the atmosphere and oceans.

Surplus in the tropics because sunlight is more direct and more intense. Deficit near the poles because of low sun angle, high albedo, and long dark winters.

Mild, wet winters allow evergreen photosynthesis while dry summers disadvantage deciduous broadleaves. They dominate west-side lowlands, mountain slopes, and the drier east side at mid-elevations.

Summer drought coincides with the warmest, sunniest period, while winters are wet but cool and dark. Plants need water conservation and tolerance of low winter light and cold.

Summer drought, cool winters, low winter light, nutrient-poor soils, frost and snow at elevation.

Large: regional climate, parent material, topography. Small: microclimate, microsite soil conditions, local disturbance, biotic interactions.

Evergreen needles with high leaf area that photosynthesize through mild winters, long-lived needles, strong tracheid wood, thick bark and resin for fire and pest defense, large water storage in sapwood, efficient nutrient use. [CHECK]

Evergreen needles photosynthesize in mild, wet winters. Needles tolerate summer drought (thick cuticle, small surface area). Needles retain nutrients for years and shed snow. Long growing season and abundant winter moisture.

Long growing season (winter photosynthesis); high accumulated leaf area from long-lived needles; abundant winter water and mild temperatures; infrequent severe disturbance allowing long lifespans; large water and carbon storage in wood.

Photosynthesize year-round in mild winters, resist summer water loss (thick cuticle, sunken stomata, small surface area), shed snow, conserve nutrients by retaining leaves for years.

Typical temperate deciduous forest: production peaks in summer and stops in winter (leafless). West-side conifers: production continues through mild winter, spring, and fall, and is limited in the dry summer by high VPD and low soil water. [CHECK]

Water availability, length of growing season, and mild temperatures (higher on the west side), plus disturbance regime (east side has more frequent fire). West side has much higher biomass.

False. West-side forests have far more total biomass because water is more available. [CHECK]

West side has much higher NPP (more water, longer growing season). East side has lower NPP, limited by water.

It becomes more negative (gravity plus longer path resistance), reducing turgor, leaf size, and photosynthesis in tall trees.

Autotrophs make their own organic matter from inorganic sources (photosynthesis). Heterotrophs get energy by consuming organic matter.

Producers (autotrophs) at the base, then primary consumers, secondary consumers, tertiary consumers. About 10% of energy passes to each higher level, so biomass and energy shrink going up.

The light level where photosynthesis equals respiration (net photosynthesis = 0).

The light level above which more light no longer increases the photosynthetic rate.

Curve rises with light then plateaus. Shade-tolerant: lower compensation point, lower saturation point, lower max rate. Light-demanding: higher compensation point, higher saturation point, higher max rate.

Light is absorbed layer by layer through the canopy, creating vertical layers. Shade-tolerant species persist below, while light-demanding species need gaps or tall canopy positions.

Flat or horizontal branches and leaves, larger and thinner leaves, more leaf area per mass, dense foliage layers, low respiration rates, more chlorophyll per leaf.

Flat (shade) leaves have low respiratory costs. [CHECK]

Positive, roughly linear at low to moderate N, leveling off at high N. N is a component of Rubisco and chlorophyll.

Advantages: avoids winter cold and drought, cheap leaves, high photosynthetic rate. Disadvantages: must rebuild leaves every year, short growing season.

Advantages: photosynthesizes in any warm period, conserves nutrients. Disadvantages: costly leaves, lower photosynthetic rate, year-round respiration and winter damage risk.

Light (energy), temperature (enzyme activity), CO2 (substrate), water (stomatal opening), nutrients (especially N), VPD (stomatal closure).

Photosynthesis is enzyme-driven (e.g., Rubisco). It is slow when cold, peaks at an optimum, and declines when hot (enzyme damage, stomatal closure, photorespiration).

Sun leaves (top) are smaller, thicker, with higher photosynthetic capacity. Shade leaves (lower) are larger, thinner, with more chlorophyll per mass.

6 CO2 + 6 H2O + light energy -> C6H12O6 + 6 O2

NPP = GPP - autotrophic respiration (Ra)

Carbon gained per unit water lost (e.g., mol CO2 fixed per mol H2O transpired).

Thick waxy cuticle, sunken stomata, small or needle leaves, stomatal closure, deep roots, mycorrhizae, evergreen needles with low surface area, water storage in sapwood.

Photosynthesis removes CO2 from the atmosphere and builds organic carbon. Respiration returns CO2 to the atmosphere.

Nitrogen (N), phosphorus (P), potassium (K).

Carbon, hydrogen, oxygen (from atmospheric CO2 and from water). [CHECK]

Roots absorb dissolved ions from soil water via mass flow, diffusion, and root interception, aided by mycorrhizae and exchange of nutrients held on clay and organic matter.

Nitrogen commonly limits plant growth on land (soil). In freshwater, phosphorus is usually more limiting. [CHECK]

By maintaining infiltration and filtering capacity, preventing erosion and compaction, using riparian buffers, and limiting excess fertilizer to reduce nutrient and sediment runoff. [CHECK]

Improves structure, water holding and infiltration, nutrient supply and retention (CEC), feeds soil microbes, and reduces erosion and compaction.

Enormous: roughly billions of bacteria per gram of soil plus many fungi and thousands of species. [CHECK]

Soil zone immediately around roots, influenced by root exudates. It has intense microbial activity and is important for nutrient uptake, mycorrhizae, and nitrogen fixation.

Climate, Organisms, Relief (topography), Parent material, Time. Each controls weathering rate, organic input, water movement, starting minerals, and soil development.

Sand (0.05-2 mm), silt (0.002-0.05 mm), clay (<0.002 mm).

Clay (smallest pores).

Water held in small soil pores by adhesion and cohesion, available to plants.

Water remaining in soil after excess has drained by gravity (usually after 1-3 days).

All soil pores are filled with water.

Surface organic layer of litter and decomposing material.

Mineral topsoil darkened by mixed-in organic matter.

Light-colored leached layer where clay, iron, and organics have washed out (eluviation).

Unweathered solid rock beneath soil.

Compaction squeezes pores, reducing aeration, water movement, and root penetration. Very high compaction = shallow roots. Very low compaction = loose soil that may hold less water and give weaker root anchorage. [CHECK]

Inputs from litter and roots; losses by decomposition and respiration. Storage time is controlled by temperature, moisture, litter quality, clay and mineral protection, oxygen, and disturbance. It ranges from years to millennia.

Gaseous (atmospheric reservoir) and sedimentary (rock/soil reservoir).

Carbon, nitrogen, oxygen (and hydrogen, sulfur).

Matter is conserved: inputs - outputs = change in storage, so you can account for how elements enter, leave, and accumulate.

Atmospheric deposition, N fixation, rock weathering, CO2 uptake, fertilizer, and flow from other areas.

Leaching and streamflow, erosion, gas emissions (e.g., denitrification, respiration), fire, harvest.

The watershed, because water carries elements and inputs and outputs can be measured at defined boundaries (e.g., stream outflow). [CHECK]

Trees fix CO2 via photosynthesis (GPP), some is respired (Ra), the rest becomes NPP in biomass. Litter and roots enter soil, decomposers return CO2 via respiration, and disturbance moves carbon out.

Mainly burning fossil fuels, which consumes O2. The decline is very small compared with the total atmospheric amount. [CHECK]

Humans appropriate a large share of terrestrial NPP (HANPP), and boundaries for nitrogen and phosphorus cycling have already been exceeded.