Biodiversity

Chapter 3

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Unit Organization:

• Single Origin Theory
• Brief History of Life
• Biodiversity
• Biome Survey
  • Terrestrial Biomes
  • Aquatic Biomes

Reading:

Textbook: Chapter 4

Ancillary Reading:

Single Origin for Life

Origin of life can be seen as a multistep accumulation of chemical complexity

have to explain how self-replication, control of metabolism, and information storage arose from chemical interactions under the conditions prevailing over 3 billion years ago

Evidence for a Single Origin

Looking for common features of all living things that are common to all due to history, not function

• Universal genetic code
• Use of L-amino acids
• Ribosomal RNA sequence
• Conserved amino acid sequence for non-functional portions of some proteins
• Conserved codon usage for redundant codons
• Use of ATP for vast majority of metabolic reactions

Brief History of Life

Major Features

• 4.5 bya      -  Origin of Earth
• 3.8 bya      -  Origin of life
• 2.8 bya      -  O₂ appears in the atmosphere
• 2.1 bya       -  Eukaryotes appear
• The time since the origin of the Earth has been divided into four "eons"
  • The first eon covers up until life appears
• The most recent eon, the Phanerozoic, covers from the sudden appearance of many fossils about 560 mya up until the present
• The sudden appearance (sudden in terms of geological time) of many hard-bodied fossils is called the Cambrian Explosion and probably was due to the rise of predation as a mode of living (the hard bodies are protection from the newly evolved predators)
• Thus, the fossil record only really covers the last 0.5 bya, or 1/9th of the age of the Earth, and life has been here for over 7/9ths of the Earth's history
• The Phanerozoic Eon (560 mya to 250 mya) is divided into three "eras": the Paleozoic (old animal), Mesozoic (middle animal) and Cenozoic (recent animal) eras
  • The Paleozoic era (560 mya to 250 mya) - origin of land plants and animals, origin of coal deposits from large swamp forests
    • Neither mammals nor flowering plants were found in the Paleozoic
  • The Mesozoic era (250 mya to 65 mya) - rise of reptiles, origin of both mammals and flowering plants, and finally, the decline of the reptiles
    • Pangea, the most recent supercontinent, breaks apart during the Mesozoic and the pieces drift to their present positions as the continents
  • The Cenozoic era (65 mya to today) - rise of the mammals, new peak in biodiversity

Mass Extinctions

The extinction rate varies over geological time and, at five times in the past, has spiked, causing the lost of a large portion of existing biodiversity

• If 75% of all species go extinct, it is deemed a mass extinction
• The transitions from Paleozoic to Mesozoic (Permian-Triassic mass extinction) and Mesozoic to Cenozoic (Cretaceous mass extinction)
  • Permian-Triassic (also known as the Great Dying) was devastating to biodiversity - 96% of marine species , 70% of terrestrial vertebrate species, 83% of all insect genera lost
    • Probably multiple causes (increased volcanism, burning of large coal fields, marine methane clathrate breakdown) - 85% of all species went extinct
  • Cretaceous-Paleogene (used to be the Cretaceous-Tertiary or the K-T [K for the German term "Kreidezeit") event
    • Multiple causes (Bolide collisions, sea-level changes, Volcanic eruptions of the Deccan Traps)
    • Loss of sunlight seems to have had an effect (less extinction for organisms and systems not directly dependent on sunlight)
• Sixth Mass Extinction
  • Evidence is accumulating that the current rate of extinction for many groups matches the rate of extinction seen in a mass extinction, if you assume that the ancient mass extinctions occurred over the time it would take to perform a mass extinction on vertebrates at the current rate of extinction (about 500 years)
    • Barnosky, A.D.  2011.  Has the Earth's sixth mass extinction already arrived?  Nature 471: pp 51-57.
    • Actual mass extinctions occur over much longer periods and have lower rates over those longer periods

Biodiversity

A stable climate and time have resulted in an unprecedented accumulation of species since the most recent mass extinction, the Cretaceous-Tertiary extinction.

• Time (the x-axis) on the graph above goes back as you go from left to right
• ¹⁸O is an Isotope of Oxygen that is slightly heavier than ¹⁶O, by far the most common oxygen isotope
  • Water with more ¹⁸O will tend to sink below the surface than water with ¹⁶O
  • Water molecules with ¹⁸O will require more energy to vaporize (and will liberate more energy when condensing) than water molecules with ¹⁶O
• The above facts mean that, as temperatures rise, more O16 water evaporates than ¹⁸O water (and more ¹⁸O18 water than ¹⁶O16 water condenses as temperatures cool)
  • Thus, the ratio of ¹⁸O to ¹⁶O in the oceans changes with changes in ocean temperature (more ¹⁸O when hot, less when cool)
  • Calcium carbonate formation uses water, so the fossil shells from warm oceans have less ¹⁸O than the fossil shells from cooler periods

The driving force behind the origin of new species is evolution by natural selection.

• We do not have a good grasp of total global biodiversity
• Is there value to biodiversity?
  • More biodiverse systems are more stable
  • More biodiverse systems provide greater system services (fresh water, cleaning air, etc.)
  • Greater potential for valuable species

Measuring Biodiversity

Species richness (total number of species) is the most common way to do this

Two islands

• Island 1 has 5 species and Island 2 has 5 species.
  • Which is the most diverse?
• Island 1 has 2000 of species A, 10 of species B, 10 of species C, 5 of species D and only 1 of species E.
• Island 1 has 500 of species A, 450 of species B, 400 of species C, 350 of species D and only 300 of species E.
  • Which is the most diverse?
• Both have the same species richness but Island 2 has greater evenness so it is more diverse

Species diversity indices (or indexes, if you prefer that plural) have both richness and evenness components

Biogeography

Biogeography is the study of how species are spread about spatially.  This is an important component of biodiversity but we will cover this at a later date

Biome Survey

Biomes are community types often the result of a few important physical factors

Biomes are types and many specific examples may exist (Deserts occur in almost all continents)

Terrestrial Biomes

Climate is the aggregate of yearly prevailing weather conditions, such as temperature, humidity, precipitation, air pressure; and is often important in determining the location of terrestrial biomes and here are some climate types:

• Tropics -from 23.5°N (Tropic of Cancer) to 23.5°S (Tropic of Capricorn)
  • Day length varies little throughout the year
  • Warm, moist weather
• Temperate Zone - ~30 to 50°, both north and south hemispheres
  • Warm summers, cold winters
  • Moderate to Low rainfall
• Boreal Zone - ~50 - 66.5°, both north and south
  • cold winter, short summer
  • relatively high levels of precipitation
• Polar Zone - above 66.5° Latitude
  • low rainfall and very cold winters
• Mediterranean Climate
  • dry, hot summers with cool, moist winters
  • Found around the Mediterranean Sea, southern California, Central Chile, Cape region of South Africa, Southwestern and Southern Australia, and Northern Argentina
• Subtropics
  • region between tropics and temperate zone
  • warm and moist to warm and dry
• There are also other "general influences" on the climate in a region
  • Continental and Oceanic effects
    • Land heats and cools faster than Oceans
    • So, in general, the interior of continents have wider ranges in climate conditions than do islands or coastal regions
  • Montane effect - Mountains can cause climatic effects
    • Adiabatic Cooling - cooling of air as it rises - caused by expansion as pressure is reduced
    • air loses the ability to carry moisture as it cools, so the relative humidity increases as air rises and moisture condenses out so rain falls on side of mountains where moist surface air is pushed up the mountain
    • rain shadows on the side of mountain where cool air is descending after being pushed over the mountain (it has lost it moisture)
    • mountains can change circulation patterns on a continental scale

Tropical Rain Forest

• Abundant rainfall in all seasons and warm temperatures
  • Long growing season, little seasonal variation, high rate of photosynthesis (primary productivity high)
• Soils are leached by rainfall (soluble nutrients removed)
• High diversity of plant and animal life and lots of biomass/acre

Tropical Deciduous (Dry) Forest

• Abundant rainfall only in one season and warm temperatures
  • Shorter growing season than rain forest, little seasonal variation in temperature
  • Trees are drought deciduous, dropping their leaves when the soil dries out
• High rate of photosynthesis (primary productivity high)  during wet season
• High diversity of plant and animal life

Tropical Savannas

• Dry areas with grass as the ground cover and occasional trees and shrubs
• Warm climate with seasonal rainfall insufficient for  forest development
  • Differ from Mediterranean Climate in that the rainfall comes during the warmer season
• Often occur on flat lands with nutrient-poor soils

Desert

• High daytime temperatures (Warm Deserts), except at high latitudes or elevations (Cold Deserts)
• Water limiting (lack of rainfall due to latitude or to Rain Shadow effect of mountains)
• Large daily temperature variation
• No trees, Plants dominated by:
  • Annuals - grow only during wet periods (may not be "annual")
  • Succulents that store water in stems or leaves
  • Root Succulents that store water in underground swollen roots
  • Deciduous Shrubs - drop leaves when water is limiting
  • Plants often have thorns or spines to protect water resources
• Plant cover may cover less than 10% of soil (none in some areas)

Temperate Deciduous Forest

• Moderate rainfall , Temperature goes below freezing, but not to extremes
• Trees species dominated by a small number of species (or related species, like the oaks or maples or hickories)
  • Growing season ends with onset of cold weather and loss of leaves
  • Trees shorter than in rain forest, but canopy is closed
• Plant and animal diversity lower than in tropical rain forest
• Found in Eastern North America, Mid-latitude Europe, Japan, Northern China, India

Temperate Shrublands

• Occur in areas with a Mediterranean climate
• Xeric (dry) evergreen shrubs and small Chlorophyll (with tough leaves having thick cuticles) trees
• Called Chaparral in North America, Matorral in South America, Fynbos in South Africa
• Often subject to a constant fire regime, burning during the dry season

Grasslands

• Temperate climate, Rainfall too little for trees, enough to support 100% ground cover
  • grasslands often found between deserts and forests
• Fire a factor in maintaining grasslands
  • Most of the biomass of many grassland plants is below ground, where most fires will not kill the plant
  • For millennia, Humans have kept some landscapes grassland rather than dry forests by setting fires at regular intervals
• Grazing mammals also a factor
  • Large herds (buffalo) kill young trees
• Lack of moisture slows decomposition so the soils are very rich in organic material
  • Best soils for grain agriculture
  • Little natural grassland left

Boreal Forest (Taiga)

• Moderate rainfall during the short, cool summer, Severe winters, drier than the summer season
• Forest dominated by Conifer Trees
  • Low diversity, but population numbers can be very high
  • short growing season means the annual productivity of these forests is lower than temperate or tropical forests

Tundra

• Low rainfall, although Permafrost keeps soils moist, Extreme cold, short growing season
  • Permafrost is a layer of frozen soil.  Soils freeze and thaw from the top, where they are warmed by the sun.  If the warm season is too short, the lower portion of the frozen soil doesn't melt - this is the permafrost.
  • Permafrost is water-proof and so no moisture that falls on soils underlain by permafrost percolates into the lower groundwater and no groundwater with nutrients can move up
• Shrub and small trees only, much open grassland
• Repeated freeze-thaw cycles over many years push the soil into regular shapes.  Click on the name to see a website with pictures
• Many migratory animals present during summer months only (many birds nest in the tundra)
  • Many biting insects

Some other terrestrial biomes

Coastal Pine Forest

• Sandy, low nutrient soils, fire common
• Southern Alabama, Mississippi, coastal Carolinas and Georgia

Temperate Rainforest

• Very wet temperate climate, trees dominated by conifers

Alpine (sometimes montane is used instead of alpine)

• these communities occur as you ascend mountains and are similar to biomes you find as you go north
• Rainfall increases on windward side, decreases on leeward side (Rain Shadow)

Aquatic Biomes

Fun water facts

• Water is densest at 4° C, so the bottom of the ocean is always 4 °C
• Cold water holds more O₂ than warm water, so warm water can asphyxiate fish

Freshwater Ecosystems

Lentic habitats are wetland, lake and pond communities

• Ponds have plant and algal growth on bottom (light reaches bottom) and no vertical zonation, whereas lakes have water deep and/or dark enough so that the bottom has no photosynthesis occurring and have vertical stratification
• Lakes and ponds are, in general, temporary features of the landscape because they fill in over time
• Aquatic organisms that live off of the bottom in the water column (in fresh or marine ecosystems) can be:
  • Plankton - usually small organisms that drift freely in the water
  • There are many bacteria and viruses found in the plankton
  • Phytoplankton - unicellular algae
  • Zooplankton - protistans
  • Nekton - animals that can swim against currents and do not drift
• Lakes can be divided into zones using more than one scheme.
  • Thermal Lake stratification -
  • Photosynthetic Zonation

  Freshwater Wetlands

• Important - 6% of terrestrial habitat - but tend to be local and small
  • range from constantly flooded land to soils that are only episodically saturated with water
  • water saturation leads to anoxic conditions that are tolerable for plants adapted to flooded soils
  • wetlands develop in three topographic situations:   shallow basins. shallow river banks. and lake fringes
• Types of wetlands
  • Marsh - wetlands with emergent herbaceous (non-woody, like the grasses in a salt marsh) vegetation
  • Swamp - wetlands with emergent woody vegetation (trees, usually)
  • Riparian Woodlands (Bottomlands, Bosque) - wetland woods along rivers, may be seasonally
  • Peatland (Mire) - wetlands with an accumulation of undecomposed plant material (Peat)
    • Bog - mires with precipitation as the primary input of water, unproductive as there is no source of nutrients other than rainwater and acidic because the anoxic decomposition produces lots of organic acids
    • Fen - mires with a source of groundwater as their primary input of water, more productive than bogs because of the nutrient input by the groundwater flow
    • Quaking Bog - when a lake is overgrown by Sphagnum, the overgrowth can form a layer so thick that you can walk on it, although it will "quake" when you do so
  • Flooded Grasslands (and Flooded Savannas) regions that are regularly flooded, usually seasonally but some, like the Sudd and the Everglades, are flooded all year. these are productive ecosystems of moderate diversity and endemism

  Lotic Ecosystems are running water - stream and river - No clear distinction between stream and river except size and no clear point at which streams become rivers

  • Watershed - a geographical region that is drained by a single stream or river, including all of the Tributaries (streams or rivers that are upstream and flow into a stream or river - sometime called Headwaters) of that stream or river
• Lotic ecosystems are affected by the rate of water flow, which depends on the slope (steepness)of the stream and the volume of water flowing
• Stream Drift
  • Debris and the organisms that feed on them are carried downstream by the constant flow of water
  • Adult insects are responsible for moving upstream by flying there

Freshwater-Marine Interface - Estuaries, Barrier Islands, Mangrove Forests and Salt Marshes

• Estuaries are where fresh and salt water mix, stressful for organisms - Mudflats and marshes common - High primary productivity but low species diversity
• animals must deal with
  • maintaining their position in the marsh as tides and river flow mean that the water is constantly moving but not always in the same direction
  • adjusting to varying levels of salinity as the estuary has a gradient of salinity from freshwater in the river to ocean salinity near the mouth of the estuary and the gradient can move with the tides
• Barrier Islands form where sand is carried toward shore by waves until it piles into low islands of sand just off of the coast
• Lagoons - the waters between the coast and the back side of the barrier islands
• Mangrove Forests (Mangals) - found on tropical, low energy (sheltered, waveless) coasts - productive systems that are important fish nurseries
• Salt Marshes -mudflats in temperate regions dominated by a type of grass called cordgrass in the genus Spartina
  • high productivity areas because of the input of nutrients with each tide
    • much of the productivity is available to the predators (fish and crabs or birds and mammals) that come and go with the tides so salt marsh productivity supports coastal fisheries

Marine Communities (Oceans)

• Intertidal zone
• Pelagic Zone - the waters of the ocean
  • Neritic Zone - shallow ocean over the Continental Shelf
    • Continental shelf is the edge of the rock formations that make the continents - lighter rock that "floats" on the more dense rock of the ocean floor
  • Oceanic Zone - deep, open ocean - water column broken into zones (fish differ in each zone)
• Benthic Zone - the bottom of the ocean - mostly non-productive (food has to fall from surface - mostly mud
  • ocean averages almost 4 km deep (closer to 5 km if the neritic zones are not included in the calculation), so the benthos is:
    • uniformly cold (4°C water is densest and sinks to the bottom)
    • under tremendous pressure (~1 atmosphere for every 10 m of depth, so 4 km deep means about 390 atm, or over 5,700 pounds per square inch) from the weight of the water above
  • Volcanic vents
    • Sea floor spreading causes volcanism
      • as hot mantle material comes to the surface it cools and forms the Midocean Ridges
    • where the ridges or other volcanic activity on the sea floor is, vents can form
    • vents are home to one of the most unusual ecosystems on Earth, only discovered in 1977

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Last updated January 30, 2012