Life and the Environment

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## An understanding of the physical environment is key to understanding all ecological phenomena

![:scale 80%](figs/earth_climate.png)

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# .blue[Biomes]

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# Biomes

#### Large-scale biological communities sharing _similar_ **plant** growth forms; often owing to convergent adaptations to similar physical environments; determined largely by temperature and rainfall (climate)

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how does a particular environment result in similar plants? selective pressure lead to similar functional traits through evolution

why defined by plants? plants form the foundation of life on earth; they are primary producers

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# Primary productivity on Land

![](figs/npp.png)

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# Primary productivity in Oceans

### Almost half of all primary productivity on Earth

![](figs/ocean_production.png)

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# Ecoregions (867 distinct ones)

Olson et al 2001 _Bioscience_

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how many biomes depends on who do you ask; or how different to go

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# Major Determinants of Global Climate

### 1. Spherical shape of the earth: uneven heating

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while the global distribution of biomes is determined by climate, what determines the distributions of climate?

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# Major Determinants of Global Climate

### 2. Revolution of the Earth around the Sun on a tilted axis (seasons)

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# Seasons

![](figs/tmp.gif)

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# What is the main cause of winds?

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a. the rotation of the earth around the sun  
b. the rotation of the earth on its axis  
c. the differential heating and cooling of different geographical locations on earth
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## As air rises, it expands and cools
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# Wind is caused by differential heating of the Earth’s surface

![](figs/fire_air.png)

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![](figs/wind.png)

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# Major Determinants of Global Climate

### 3. Rotation of Earth around Earth’s axis. Creates **Coriolis effects** (conservartion of momentum)

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# Air circulation patterns (surface)

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## Ocean currents are driven by winds and redistribute heat, and modified by Coriolis effects

![](http://www.coastalwiki.org/w/images/thumb/f/f4/Ocean-Currents_gkplanet.jpg/800px-Ocean-Currents_gkplanet.jpg)

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# Rising warm airs --> Rain

![](https://anessoriginal.files.wordpress.com/2014/09/convection-rain.png?w=640)

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![](figs/precip.gif)

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## Why does it rain on the windward side of mountains, and why is it dry on the leeward side?

![:scale 80%](figs/mountain.png)

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# Rain shadow effect

![](figs/Rain_shadow_effect.jpeg)

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# Rain shadow effect

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# Climate and World Biomes

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# Tropical rain forests

Dominant canopy plants: broad-leaved evergreen trees

Also epiphytes, lianas, palms, and generally sparse understory

More-or-less continuous 
growing season

Contain ~50% of Earth’s species & ~37% of terrestrial carbon in ~11% of terrestrial veg. cover
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# Tropical seasonal forests and savannas

Thorn woodlands

Tropical savannas

Generally smaller-stature trees and more deciduousness than in rain forests

Resource availability, fire & large herbivores help determine the balance between grasses vs. woody species

Pronounced wet / dry seasons
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# Deserts

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Populations of plants & animals are often sparse (owing to resource limitation)

Succulence (fleshy water-storage tissue in leaves, stems, etc.) is common among the plants

Sustained periods of high temp. & low water avail.

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# Temperate Grasslands

Greater temp. variation than tropics

Relatively warm, moist summers & cold, dry winters

Some have sufficient rainfall to support woody veg., but fire & grazers maintain grasslands

Soils rich in organic matter (especially from proliferation of grass roots)

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# Temperate Shrubland and Woodlands

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Winter rainy season (e.g., Mediterranean-type climates – water and temperature conditions for growth are somewhat asynchronous)

Fire is a common feature

Evergreen, sclerophyllous (tough, leathery) leaves are common
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# Temperate Deciduous Forests

Deciduous leaves owing to freezing temperatures

Sufficient rainfall & soil fertility to support tree growth (trees largely outcompete grasses)

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# Temperate Evergreen Forests

Generally on nutrient-poor soils

Northern Hemisphere – 
needle-leaved conifers

Southern Hemisphere – 
needle-leaved & broad-leaved trees

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# Boreal Forests / Taiga

Coniferous tree species in continental climate zones and deciduous birch forests in some maritime zones

Extreme weather

Permafrost common

Largest terrestrial biome, with ~33% of forested land

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???

Immense carbon pool

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# Tundra

Dominated by sedges, grasses, forbs, lichens, mosses 
& prostrate shrubs

Primarily in the Arctic

Extreme weather and adaptations for prolonged dormancy

Permafrost very common
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# Mountains: A Diversity of Biomes

![](figs/mountains.png)
.right[[Elsen et al. 2018](https://paulelsen.files.wordpress.com/2019/10/elsen-et-al.-pnas-2018.pdf)]