Biogeography and Plant Ecology: Climate, Succession & History

Phylogeny

The evolutionary relationships between an ancestor taxon and its known descendant taxa

Phylogeography

An approach to biogeography that studies geographic distributions of lineages within and among taxa

Linnaeus

Described ~13,000 species

Buffon

Earth is >6000 years old and changed through time; Earth's center in the North

Buffon's Law

Environments that are similar BUT isolated regions have distinct species assemblages, though the species have similar traits

Forster

Tendency for plant diversity to decrease from the equator to the poles

Humboldt

Described 'vegetation belts' (increased elevation = decreased diversity)

Candolle

Island area, isolation, age, volcanism and climate influence floristic diversity

Lyell

Stratified layers and fossils suggest Earth and biota change through time

Uniformitarianism

Natural processes observed currently have always acted on Earth and are key to understanding the past (Lyell)

Darwin

Natural selection for speciation and differences in species diversity and composition

Dispersalists

Rare long-distance dispersal events establish isolated populations that then differentiate (Darwin's camp)

Extensionists

Land bridges (now submerged) facilitated the extension of species distributions between land masses

Hooker

Believed similarities between African and S. American floras were the result of land bridges

Wallace

Co-discovered natural selection

Hilgard

Climate and plants are responsible for converting parent material into soils

Dokuchaev

Soils have characteristic structure

Merriam

Confirmed that elevational variation in plant species composition was similar to latitudinal variation (life zones)

Wegener

Continental drift

Hutchinson

Multidimensional niche concept

What is the primary driver of plant distribution?

Climate

What determines species ranges?

Climate + soil

Lowest elevation on Earth (Dead Sea): do plants occur there?

Yes, some plants, but sparse

Highest elevation where plants are found

The Himalayas

Geographic template

Abiotic conditions vary in a predictable manner across geographic gradients; resemblance of environmental conditions decreases with distance (Earth's environments are highly unrandom)

What powers the geographic template?

Energy in Earth's core: volcanic activity, continental drift, plate tectonics

Distance decay

Similarity between communities decreases with distance

Similarity (between communities)

Degree of resemblance between communities; 0 = no species in common, 1 = all species in common

What drives Earth's climate?

Solar radiation

How does solar radiation create seasonality?

Incident radiation heats Earth's surface; the angle of incidence (tilt) drives seasonality, which drives atmospheric circulation (wind patterns), ocean currents, climate and weather

How does temperature change with elevation?

It decreases with elevation

Adiabatic cooling

Decrease in temperature resulting from a decrease in air pressure as air rises and expands

Adiabatic cooling rate: dry air

~1°C decrease per 100 m rise

Adiabatic cooling rate: moist air

~0.6°C decrease per 100 m rise

Why is it cooler at high elevation?

Air is less dense at high elevation; expansion requires energy, therefore temperature decreases

Atmospheric circulation: what happens at the equator?

Equator is heated most; rising air expands and becomes less dense, reducing surface pressure so air flows from high to low pressure; rising air undergoes adiabatic cooling

Why don't surface winds blow directly N or S?

Earth's rotation (Coriolis effect)

Coriolis effect

Apparent deflection of moving objects such as air and water currents due to Earth's rotation

Ocean current circulation: Northern Hemisphere

Clockwise (CW)

Ocean current circulation: Southern Hemisphere

Counterclockwise (CCW)

Precipitation near the equator

Adiabatic cooling of ascending air produces heavy rainfall

Precipitation at ~30° latitude

Air descends, warms and absorbs moisture, causing deserts

Precipitation at the poles

Dry

Rain shadow effect

Wind carries moist air that rises on encountering a mountain; it cools adiabatically and condenses, so precipitation falls on the windward side. Air descends after the crest, warms adiabatically, and remaining moisture does not precipitate (dry leeward side)

Major climatic regions reflect...

Temperature and precipitation patterns: latitudinal variation in temperature and regions of high and low precipitation

Primary succession

Series of community changes on uncolonized terrain (rock, lava, etc.); transformation of bare rock/sterile substrate into soil that supports an ecological community (weathering); occurs after a disturbance removes soil and its organisms and organisms above the surface

Secondary succession

Occurs when a disturbance removes some or all of the organisms but soil remains intact

Succession (general)

Gradual temporal replacement of species ending in a stable state (climax community)

Why is the concept of succession no longer widely accepted?

Because communities are dynamic

Key outcome of succession

Soil development

Soil formation occurs by...

a) Weathering of rocks via freeze-thaw cycles, water and wind erosion, lichens; b) accumulation of organic matter from dead and decaying organisms (microbial activity)

What alters soil chemistry?

Microbes and plants

What do rates of soil formation depend on?

Parent material and climate

Soil formation in the Arctic and desert

Formation of shallow soils may take 1000s of years

Eastern Canadian soils

Only a few cm deep; began forming at end of Pleistocene (~10,000 yrs ago) because of glacial history, rocky terrain, cold climate, limited biological activity, acidic conditions

Primary succession in warm/moist climates

Can occur rapidly (e.g., Krakatau)

Uniform vs. variable soils (examples)

Uniform: Great Plains; highly variable: Great Basin. Regions with high tectonic activity are more complex

Zonal soils

Soils with well-defined characteristics primarily influenced by climate (weather) and vegetation of the region; result of dominant pedogenic processes within a particular climate zone

Examples of parent materials

Sandstone, shale, granite, gneiss, slate

Pedogenic regimes

Dominant soil-forming processes that occur under certain climate conditions

Four major pedogenic processes

Podzolization, laterization, calcification, gleyzation

Podzols: conditions

Low temperatures inhibit microbial activity, causing organic matter (humus) accumulation

Podzols: process

As humus decays, organic acids leach minerals and nutrient cations from soil and replace them with H+ ions (acidification); coniferous forests thrive on these soils

Latosols: conditions

High temperature and rainfall increase microbial activity, therefore decrease humus accumulation

Latosols: process

Soluble minerals leach, decreasing fertility; iron oxide and Al accumulate to form a hard red clay layer (laterite)

Calcareous soils: conditions

Low rainfall and high evaporation, therefore low cation leaching

Calcareous soils: deserts vs. grasslands

Deserts produce a shallow rock-like layer of calcium carbonate; in grasslands (more rain), water and roots penetrate further to produce deep fertile soil

Gleyed soils (gleyzation): conditions

Low temperature and waterlogged/frozen soils prevent decomposition, so acidic organic matter builds up

Gleyed soils: characteristics

Blue/grey clay; low leaching BUT acidic conditions bind nutrients in chemical compounds unavailable to plants

Unusual soils: three types

1) Derived from parent materials of unusual chemical composition; 2) Halomorphic soils; 3) Acidic soils (gleys)

Unusual soil examples: unusual parent material

Gypsum (excess sulfate); serpentine (low Ca:Mg ratio; low N, P, K; high Ni and Cl); dolomite (high in Ca2+)

Halomorphic soils

High Na+, Cl-, sulfates; e.g., salt flats

Halophytes

Salt-loving plants; have problems maintaining osmotic and ionic balance

Acidic soils (gleys): effect

Bind essential nutrients in inaccessible compounds

Geographic range

Area in which parts of a species are distributed; a range map depicts this

Three ways to depict a species' range

1) Outline map: depicts geographic limits (range boundaries); 2) Dot plot: plots points on a map where species have been recorded; 3) Contour map: uses isolines to illustrate changes in characteristics across a geographic range

Four limits of species range

1) Climate; 2) Species interactions; 3) Habitat; 4) Dispersal

Fitness across environmental gradients

Fitness varies across environmental gradients

Multidimensional niche

Several factors interacting in hypervolume to limit species geographic distribution

Liebig's law of the minimum

Plant growth is limited by the scarcest resource

Three things that limit geographic range (list)

1) Temperature; 2) Competition; 3) Water availability

Treeline

Boundary defining where trees are capable of growing; determined by temperature, water availability, wind and snow depth; trees are slow growing with long lifespan

Krummholz ('crooked wood')

Branches only on one side, caused by wind at treeline

Source habitat

Birth rate > death rate but density doesn't exactly increase; emigration > immigration; produces lots of seeds that disperse into other environments

Sink habitat

Death rate > birth rate; receives seeds from source; immigration > emigration

Metapopulation

Set of subgroups of a species that are linked by gene flow

Clements' view of communities

Communities are like superorganisms; ecosystem function is hierarchical; some species have strong influence on others; certain plants occur in particular climates; species distributions do NOT overlap

Gleason's view of communities

Communities are the coexistence of relatively independent species in the same place at the same time; occurrence of species depends on individual capacity to migrate and grow in local environment; more support; distributions overlap (individualistic)

Abrupt change in species composition occurs when...

There is a high degree of environmental discontinuity

Gradual transitions occur when...

Two environments are relatively similar

Ecotone

Contains species from both communities that may be uniquely adapted

Coenocline

Graphical method (developed by Whittaker) to illustrate change in local abundance of a group of species along an environmental/geographic gradient

Coenocline Hypothesis A

Species distributed as discrete communities with sharp boundaries; competitive exclusion; Clementsian view

Coenocline Hypothesis B

Some species abruptly exclude one another along sharp boundaries but most species are not closely associated with others to form communities; hybrid Clementsian + Gleasonian

Coenocline Hypothesis C

Species distributed as discrete communities which gradually replace each other; evolved to coexist

Coenocline Hypothesis D

Species appear and disappear gradually behaving as if independent of each other; neither competitive exclusion NOR formation of communities; Gleasonian view

Coenocline Hypothesis E

Most species nested within range of few dominant species but otherwise occur independent of each other; ordered on large geographic scale BUT random at local scale

Biome

Natural vegetation that occurs wherever a particular set of climate/soil conditions exist

Tropical biomes: general features

Heavily influenced by ITCZ; trade winds of N and S hemispheres converge; near equator = huge amounts of rain; some rainfall seasonality but NO temperature seasonality

Tropical rainforest

Most productive biome with high decomposition rate and rapid leaching of nutrients; infertile (oxisol) soils; large rapidly growing evergreens forming closed canopies with shallow roots