Ecology Notes

Ecology

BIOL 241 Spring 2025

What is Ecology?

• Oikos = household; logos = knowledge
• Ecology: The scientific study of how organisms interact with each other and their environment
• Abiotic = physical attributes
  • e.g. atmosphere, climate, soil, water
• Biotic = living attributes
  • e.g. plants, animals, microbes

Ecological Systems - Hierarchy

• Ecological systems form a hierarchy:
  • Organism
  • Population
  • Community
  • Ecosystem
  • Landscape
  • Biome
  • Biosphere

Ecological Applications

• Conservation
• Restoration
• Mining
• Environmental remediation
• Invasive species management
• Reintroduction
• Extirpated species
• Endangered species
• Natural resources management
• Environmental planning
• Environmental Policy
• Ecosystem services
  • Provisioning
  • Regulating
  • Supporting
  • Cultural

The Environment

• Abiotic (Physical) Factors:
  • Light
  • Climate
  • Temperature
  • Humidity/Precipitation
  • Wind
  • Geology
  • Topography/altitude
  • Soil (Terrestrial ecosystems)
  • pH
  • Salinity
• Biotic (Biological) Factors:
  • Plants
  • Animals
  • Fungi
  • Bacteria and other microbes
  • Metabolic wastes and organic debris

Types of Species Interactions

Plant Competition

• Plants compete mostly by exploitation, excluding others of the same or smaller size
  • Light
  • Moisture
  • Nutrients
  • Thinning

Plant Competition - Interference

• Plants sometimes compete via interference
  • Allelopathy
  • Also described as Amensalism

Predation (+/-)

• Examples:
  • Pitfall traps
  • Pitcher plants
  • Snap traps
  • Venus fly trap
  • Adhesive traps
  • Sundews
  • Butterworts
  • Suction traps
  • Bladderworts

Herbivory (+/-)

Parasitism (+/-)

• Examples:
  • Mistletoe (Hemiparasitic)
  • Afrothismia winkleri (Myco-heterotrophic)
  • Indian Paintbrush (Hemiparasitic)

Amensalism (0/ - ) (Asymmetric competition)

• Examples:
  • Taller plants shade out shorter plants
  • Natural pesticide juglone secreted by Black Walnut inhibits growth of nearby plants
    • Juglans nigra
  • Several species of Lupinus: allelopathy causes soil hydrophobicity
    • Lupinus arboreus

Other Interactions

• Mutualism (+/+)
  • Plant and mycorrhizal fungi
• Commensalism (+/0)
  • Plant as habitat

Roles of Plants in Ecosystems

• Basal species in terrestrial ecosystems
• Plants can play a major role in community structure
• Habitat
• Keystone species
• Carbon sequestration
• Nutrient cycling
• Soil builders

Community Dynamics

• Succession: The change in community structure over time
• Example stages:
  • Lichen
  • Bare rock moss stage
  • Annual herb stage
  • Perennial herb stage
  • Scrub stage
  • Forest
• Ecological succession

Primary Succession

• Occurs on newly-exposed substrate that has never supported a community.
  • Lava flows forming new land mass
  • Rock outcrop
  • Cliff face
  • Sand dunes
  • Newly exposed glacial till
• Example: The Isle of Surtsey

Secondary Succession

• Occurs on sites that previously supported a community after disturbance.
• Disturbance is any process that results in the partial or complete removal of the existing community.
• Examples:
  • Tubbs fire, Sonoma Cty
  • Chernobyl
    • Pre-meltdown, 1986
    • 2016

Biomes (Terrestrial Ecosystems)

What is a Biome?

• Biomes are distinct biological communities that have formed in response to a shared physical climate and have very similar dominant plant types.

Climate and Latitude

• Relationship between climate type and latitude:
  • North Pole: 90 N (Arctic)
  • Arctic Circle: 66.32 N (Arctic)
  • Temperate
  • Tropic of Cancer: 23.5 N (Tropical Wet and Dry)
  • Equator: 0 (Tropical Wet)
  • Tropic of Capricorn: 23.5 S (Tropical Wet and Dry)
  • Temperate
  • Antarctic Circle: 66.32 S (Arctic)
  • South Pole: 90 S (Arctic)
    There exists a relationship between Latitude, Altitude, Season, etc.

Terrestrial Ecosystems/Biomes

• Boundaries between biomes are indistinct
• Main controlling factors:
  • Climate
    • Temperature
    • Precipitation
  • Topography
  • Soil (and underlying bedrock)
  • Disturbance
• Temperature + Precipitation are related to LATITUDE

Terrestrial Ecosystems - Plant Forms

• Dominant plant forms:
  • Trees (Forest)
  • Shrubs (Shrubland)
  • Grasses (Grassland)

Plant Forms

• Carbon allocation (C:N)
• Herbaceous
  • Grasses
  • Forbs
• Shrubs
• Trees
• Leaf Form
  • Deciduous
    • Winter
    • Drought
  • Evergreen
    • Broadleaf
    • Needle

Biome Distribution

• Distribution of biome types is determined by climate and reflected in dominant plant form and leaf form:
  • Tropical rainforest: Warm wet climates dominated by broadleaf evergreen trees
  • Savannah: Warm with distinct dry season, drought deciduous trees with deep roots, shrubs, grasses
  • Desert: Hot and very dry, dominated by shrubs
  • Temperate deciduous forest: Seasonal environment, dominated by winter deciduous trees
  • Temperate grassland: Seasonal environment with lower precipitation, dominated by grasses
  • Conifer forest: Cold climate dominated by needle- leaf evergreen trees
  • Tundra: Cold, short growing season, dominated by shrubs, grasses, mosses and sedges

Tropical Rain Forest

• Equatorial zone (Latitude: between 23.5^o north and south of equator)
• Location: Amazon basin and northern S. America, S Central America, SE Asia, W. Africa (Congo), Madagascar, NW Australia, Hawaii and S Pacific Islands
• WARM and MOIST; Mean temp. >18^o C, Minimum ppt >60mm/mo
• No seasons
• High diversity of plant (dominated by broadleaf evergreen trees) and animal life
• High rates of NPP, decomposition, and nutrient cycling

Tropical Dry Forest

• Latitude: 10-20^o north and south
• Location: S. Mexico, Bolivian lowlands, Pacific coast of S. America, east Coast of S. Africa, Central India, Indochina, Madagascar, New Caledonia
• Greater seasonality than tropical rain forests; Warm with distinct dry season that can last up to 8 months
• Dominated by drought deciduous trees (deep roots), shrubs, grasses, abundant vines
• High biodiversity, though not as high as Tropical Rainforest, though higher biomass of mammals
• Many of these forests have been lost to agriculture

Tropical Savanna

• Equatorial zone (Latitude 5-15^o north and south)
• Location: East Africa (Serengeti); cerrado, campos and llano of South America; mulga and brigalow of Australia
• Warm, wet season and lengthy dry season
• Largest savannas found in Africa
• Usually found bordering tropical rainforest
• Coexistence of trees, shrubs, and grasses controlled by precipitation and soil type
• Highest NPP, decomposition, and nutrient cycling during wet season
• Fauna: Large migratory ungulate herbivores, Large predators, Burrowing animals, Termite mounds

Deserts

• Latitude: Variable, mostly between 15-30^o in northern hemisphere
  • Temperate: Mountain rainshadow or far inland
  • Subtropical high: Atmospheric high pressure belt
  • Polar
• Location: Mojave, Namib, Sahara, Gobi, Atacama, Australia
• Air around the Tropics of Capricorn and Cancer is dry (Hadley cell)
• Some deserts are found on the western edges of continents (e.g. Namib desert) due to cold ocean currents, which run along the coast that make it harder for the air to hold moisture.
• Some deserts form in the rain shadow of mountains, eg the Atacama Desert is located in the rain shadow of the Andes
• Very dry (hot, cold, temperate), rainfall: <50 cm per year; Temps range: -18^o C -- 49^o C
  • Four major types:
    • Hot and dry (e.g. Sahara)
    • Semi arid (e.g. Great Basin NA)
    • Coastal (e.g. Namib)
    • Cold (e.g. Gobi)
• Low rates of NPP, decomposition, and nutrient cycling
• Vegetation: dominated by shrubs:
  • Desert scrub (e.g. sagebrush)
  • Halophytes (e.g. saltbush)
  • Succulents (e.g. aloe vera, cacti, yucca)
• Drought- evading/resistant animals: reptiles, insects, small herbivorous mammals

Temperate Grasslands

• Temperate zones: North of Tropic of Cancer or South of Tropic of Capricorn (23.5^o latitude)
• Location: N. American prairies, Eurasian steppes, Argentinian pampas, S. African veldt, also in Australia and New Zealand
• Seasonal environment with lower precipitation, rainfall: 25 -80 cm per year; NPP dependent on rainfall
  • Low ppt: Shortgrass prairie, desert grassland
  • Higher ppt: Tallgrass prairie, mixed-grass prairie
• Dominated by grasses and herbaceous plants
• Rich soil; many converted to agricultural land

Temperate Forest

• Humid midlatitudes: North of Tropic of Cancer or South of Tropic of Capricorn (23.5^o latitude)
• Location: Eastern N. America, eastern China, Japan, Korea, Taiwan, Europe, southern Chile, SE Australia, New Zealand
• Distinct seasonal environment (spring, summer, winter, autumn)
• Adequate rainfall in growing season 75-150 cm per year
• Average annual temperature 10^o C
• Thick layer of leaf litter yields nutrient-rich soil

Conifer Forests (Boreal forests or Taiga)

• Latitude: Circumpolar belt across northern hemisphere 50-65^o N
• Location: N. America, N. Eurasia
• Cool, temperate: Short cool summers, long, harsh, dry winters with prolonged periods of snowfall
• Low NPP. Permafrost maintains high soil moisture, slows rates of decomposition and nutrient cycling
• During drought, fire prone

Arctic Tundra

• Latitude: Polar region of northern hemisphere
  • North of 60^o in N. America, North of 70^o in N. Eurasia
  • (Alpine Tundra: Function of altitude. Rocky Mts, Andes, Alps, Tibet)
• Arctic zone, cold and dry. Short cool summers, long, harsh, dry winters with prolonged periods of snowfall
• Characterized by:
  • Deep permafrost
  • Overlying organic + mineral soil (freeze/thaw)
  • Vegetation that reduces warming and thawing in summer
• Plants: low growing grasses, sedges, mosses, lichens, dwarf shrubs and trees
• Low rates of NPP, decomposition, nutrient cycling

Mediterranean

• Latitude: Between 30-45^o north and south of equator, on western edge of continents
• Location: Mediterranean basin (southern Europe and North Africa), California, Chile, South African cape, SW and southern Australia
• Hot dry summers
• Mild wet winters
• Highland locations experience colder winters, prohibit growth of “typical Mediterranean plants
• Rainfall: <50 cm per year
• Plant communities adapted to drought, fire, flood

Mediterranean Vegetation

• Xeric broad-leaf evergreen shrubs
• Small trees
• Spiny, wooly or sclerophyllous leaves to retard water loss
• Aromatic plants
• Examples:
  • Fynbos, South Africa
  • Mattoral, Chile
  • Maquis, Mediterranean
  • Kwongan, Western Australia
  • Chapparal, California