Lec 21-22: Biodiversity Flashcards
ecological consequences of extinctions
- Extinctions reduce ecosystem functioning and efficiency
a diverse assemblage of species uses resources more efficiently and may facilitate each other
- a diverse group of species is insurance in a fluctuating environment
species function optimally at different parameters
Therefore, diversity insures that “jobs” are performed under varying conditions
freshwater invertebrate predators can reduce vectors of human disease
“backswimmers” feeds on mosquito larva
older ponds are more likely to be colonized bythe backswimmers
newer ones will have mosquito larva pretty quickly (will take time before backswimmers arrive)
the biosphere
the biological component of the earth’s system
the “global ecosystem”
all living organisms + dead organic material + interaction with other earth systems
all biodiversity and biological functions
(photosynthesis, respiration, decompositions, n-fixation etc)
exchanges matter ad energy with the other spheres
drives global biogeochemical cycling of some key elements
has evolved over time and has altered other components of the earth system
what is “life” a chemical Darwinian definition
life is a self-sustained chemical system capable of undergoing Darwinian evolution
“darwinian evolution” = reproduction, mutation and natural selection
“self-sustained” = contains all genetic information requited for growth and reproduction
a functional definition of life
- carry out metabolic reactions
- defend itself against injury
- respond to stimuli
- reproduce itself
- able to evolve
thus a practical definition of life involves the ability to ingest nutrients, give off waste, grow, reproduce and evolve
what does life need?
- energy
a constant input of energy is required for growth ,
Source 1 = the sun
source 2 = chemical bond energy (energy released from the oxidation of organic and inorganic compounds - water
50-98% of an organism’s body mass
provides medium for essential chemical reactions (no water = no metabolism) - Carbon and other elements
used to construct cellular components and for biochemical reactions
organisms require 28 elements, but the bulk of their mass is composed of only 6 (C, H, O, P, N, S)
hydrothermal vents in deep ocean ridges (2000m)
water heated by molten rock in the earth’s crust ; exits the vents at temperature up to 400C
thiobacillus bacteria oxidize Fe and s compounds , thus support rich communities of organisms in the absence of sunlight
earliest record of life
australian microfossils (cyanobacteria)
stromatolites
stromatolites
sedimenatry rock formed from layered microbial mats (mostly cyanobacteria)
living and fossil ones
3.5 billion years old (oldest ones)
impact of the evolution of oxygen-producing life on the atmosphere
- atmospheric (O2) increased, while (CO2) was reduced further (through photosynthesis)
- development of the ozone (O3) layer, which screens out UV radiation
co-evolution of the biosphere and the atmosphere
impact of an oxygenated atmosphere on the evolution of life
- caused development of an ozone loyer which allowed life to flourish on land
- reduced the dominance of anaerobic bacteria
- promoted the evolution of new and more efficient types of energy use (mitochondria in eukaryotic cells)
- allowed the development of larger animals (larger animal require more oxygen)
what is a biome
a goup of ecosystems sharing similar types of flora and fauna under a similar climatic regime
plant characteristics (size, foilage structure, chemistry) determine many ecosystem properties
terrestrial biomes
tropical forest
savanna
desert
chaparral (trees and shrubs hot summer and mild wet winters)
temperate grassland
temperate broadleaf forest
coniferous forest
tundra
high mountains
polar ice
(depends on latitude)
latitude and elevation determine biome distribution
mountains are a great example of that
temperature and precipitation and seasonality
temperature precipitation and seasonality control the distribution of terrestrial biomes
evapotranspiration
transpiration + Evaporation
(trees and grass, through pores) + (taken from surface of the soil (without the plants))
green water
goes through plants
blue water
moved by runoff
NPP and evapotranspiration
NPP is strongly correlated with actual evapotranspiration (AET)
AET combines the effects of temperature and precipitation
High AET = warm and wet
Low AET = dry or cold or both
(this is all related to energy amounts needed and water movement)
annual Net Primary production
highest in warm wet regions, lowest in cold dry regions
total carbon pool and NPP per biome
Tropical forest are the highest NPP production
1/3 of earths NPP
Daily, the NPP per unit area is similar between tropical and temperate forest -> this means that the difference in yearly NPP between the two biomes is primarily related to length of the growing season
Ie tropical forests don’t really have winters
what is biodiversity (biological diversity)
the millions of plants, animals and microorganisms the genes they contain and the intricate ecosystems they help build into the living environment
the variability among living organisms and the ecological complexes of which they are part; this includes diversity within species between species and ecosystems
the variety of life at all levels (genes to ecosystems) and the ecological and evolutionary processes that sustain it
NPP and biodiversity
higher NPP = Higher biodiversity , potential for bigger food webs, more energy available
species diversity
what is a species?
a group of genetically similar organisms that can interbreed and produce fertile offspring
species diversity is typically measure as species richness = #of species per habitat
population structure
variation in behavior , age, size, morphology, amongst individuals in an area
components of biodiversity
species diversity
genetic diversity
population
communities
ecological processes
ecosystems
What is the richness of the earth’s species?
more than 2 million species described
patterns
- species richness increases with area
- species richness increases toward the tropics
- species richness declines with increasing elevation
- species richness increases with energy
angiosperms
flowering plants
why does species richness increase toward the tropics?
- the tropics have greater land mass -> more area therefore more species (however, polar regions have fewer species than similar areas in lower latitudes )
- Harsher climates at the poles (but that alone does not explain the entire gradient)
- Tropical regions have more stable climates (but if this was all that was important, there should be more species on mountain tops)
- Species-energy hypothesis: greater exposure to solar energy = greater productivity = more species can be accommodated in food webs
- Higher speciation rates (driven by energy), greater accumulation of species over evolutionary time
diversity of marine inverterbrates in the fossil record
” cambrian explosion” 600 to 500 million years bc
5 other big drops
most recent 65 million years ago, the dinos!
some generalizations about extinctions
- extinctions are common
5-50 billion species existed in earth’s history 10 - 50 million are extant today
(almost every species that ever existed has gone extinct) - species with small populations (or small ranged) are easy to kill
reasons:
- demographic stochasticity (ie bad luck)
minor glitches in reproduction or survival can wipe out a small population
(“Gambler’s Ruin”) - Small gene pool
not enough genetic variability to adapt to environmental changes (ex: cheetahs) - population is spread too thinly
mate location becomes difficult - vulnerability to small-scale environmental stress (fires, predation, disease)
- widespread species are hard to kill
extinctions occur only by the elimination of all reproducing populations
the killing agent must therefore be active over the entire range of the species
the larger the range, the more likely that some populations will be spared - extinction of widespread species may result from stresses that are not normally experienced
because evolution depends on the continuous pressure of natural selection, organisms cannot adatp to stresses they rarely experience
(passenger pigeon)
- to kill many species the stress must be applied over a wide area
the largest the area the more species contained in it (species-area relationship)
K-T mass extinction
alvarez hypothesis : K-T impact
10km asteriod = 100x10^6 megatons TNT
photochemical reaction damaged ozone layer
earthquake wildfires tidal waves
increased volcanic activity
soot blanketed planet blocking sunlight
K-T mass extinction evidence
clay layer between cretacious and tertiary rock layers
iridium abundances in clay residues from pelagic limestones
element usually found in meteriorites
high pressures: shocked quartz and tektites
the Chicxulub Crater 180 km diameter (gulf of Mexico, Yucatan)
other possible causes of prehistoric mass extinctions
- volcanic activity
eruptions could cause global cooling
lava floods could cause global warming
65 million yrs ago laval floods covered 1 million sq miles of India (deccan Traps) - A fall in sea levels
reduces marine habitat areas
oxidation of exposed organic material removes O2 and releases CO2 - global climate change
cooling, drying
