lec 24: ecosystems & global ecology

humans

• energy use accelerating & increasing

• altered habitats

• nutrient cycles disrupted

  • water

  • phosphorus & nitrogen

  • carbon

autotrophs are inefficient are capturing solar energy

• 0.8% incoming sunlight used by forest plants

• 45% GPP into production of new biomass; rest used to respiration/was lost

• photopigments absorb fraction of light wavelength

• enzyme efficiency is temperature dependent

  • warmer conditions → faster

  • dryer conditions → photosynthesis stalls

primary producers (autotrophs)

inorganic compounds → chemical energy stored in sugars

• primary source of energy flow in ecosystems

gross primary productivity (GPP)

total chemical energy produced

primary producers use GPP

GPP = R + NPP (NPP = GPP - R)

1. keep existing cells alive: cellular respiration (R)

   1. growth & reproduction: NPP energy

biomass

total amount of chemical energy in organic material

net primary productivity among geographic regions

• deserts = low NPP

• forests (tropical wet) = high NPP & high productivity

net primary productivity among biomes

• open oceans = low

  • majority of earth’s surface

• topical wet forests = high

  • occupy modest amounts of earth’s surface

• coral reefs = most productive

  • small surface area → limiting NPP contribution

food chain

series of steps

• molecules & energy travels

grazing food chain

herbivores (primary consumers) & organisms that eat herbivores

decomposer food chain

species eat dead remains

food webs

compact way to summarize energy flow & documents complex trophic interactions

nutrient cycle

• energy eventually dissipates

• sun replenishes energy

• nutrients cycled through ecosystem

  • neither gained or lost

• energy moves in form of biomass when organisms eat another

• same energy source type = same trophic level (feeding)

decomposers (detritivores)

feed on detritus (waste or dead remains)

productivity declines at higher trophic levels

• biomass greater @ lowest trophic

• biomass declines at higher levels

• 10% of energy transferred to next level

productivity pyramid

reports productivity & efficiency

• productivity: biomass produced per unit of area yearly

• efficiency: fraction of biomass transferred from one trophic level to the next

10% rule masks variation

• large mammals: more efficient biomass producers

  • smaller surface-area-to-volume ratio & lose less heat

• ectotherms: more efficient biomass producers

  • don’t rely on oxidized sugars to keep warm

  • rely on environment & spend less energy on cellular respirations

more efficient for humans to feed at lower trophic levels

humans as primary producers will receive the most energy due to one energy transfer

global water cycle

water evaporates out of oceans & precipitates over globe

• water moves from lands to oceans via steams & groundwater (water in soil)

• 0.5% water in lakes, rivers, & groundwater for drinking

• most groundwater in aquifers

aquifers

layers of porous rock, sand, & gravel saturated with water

• closed aquifers have nonporous rock layers & take thousands of years to recharge

• open aquifers can be recharged by water percolating from surface

• where humans extract freshwater

  • 40% beyond carrying capacity

water table

upper limit of underground layer of soil saturated with stored water

global nitrogen cycle

nitrogen added to ecosystems is unusable when reduced or fixed

• atmospheric (N₂) → ammonia (NH₃) from lightning-driven reactions & enzyme-catalyzed reactions in bacteria

plants only use fixed nitrogen

adding nitrogen increases productivity

• too much is harmful

  • nitrogen pollution from burning of fossil fuels → acid rain, climate change, depletion of ozone layer

  • decreased species diversity

  • eutrophication: overfertilization → algal blooms in aquatic ecosystems → oxygen-free dead zones

global carbon cycle

• ocean is largest reservoir, atmospheric reservoir is small but important

• photosynthesis incorporates carbon → tissue

• cellular respiration releases carbon from living organisms → atmosphere

• human activities add carbon dioxide to atmosphere

• burning fossil fuels move carbon from inactive geological reservoir in petroleum or coal form → active reservoir

humans increase atmospheric carbon dioxide

• cooking, heat, transportations, building, agriculture, manufacturing

• energy comes from chemical sources in organic sources (wood, coal, oil, natural gas)

fossil fuels

vast reservoirs lock inside remains of plants that died mya

• energy dense

• easily burned to produce energy

• collected in vast pockets accessible to us (coal, oil, gas)

• yield carbon dioxide as waste product of combustion

greenhouse effect explains atmospheric warming

• CO₂ is greenhouse gas

  • traps heat radiated from earth that would be lost to space

  • can be absorbed by ocean

  • increase in atmospheric CO₂

• greenhouse effect is natural consequence of CO₂’s physical properties

  • greenhouse gases include methane (CH₄), water vapor, & nitrous oxide (N₂O)

overall rise in atmospheric CO₂ & temperature, but not in solar radiation

continued warming in the future

• IPCC: 2017 temp exceeded pre-industrial levels by 1 C

  • increases of 1.5 - 2 degrees by 2100

  • 0.5 - 7 by 2300

• will be past 5 million over next 100 years

temp variation

• polar regions increase more than tropics

• ecosystems at same latitudes experience large increases

• some seasons change more

temp extremes will increase