AIM: SWBAT describe the desert /xeric shrubland biome

Please Do Now: What is an osmoregulator and why is that

relevant to the study of estuaries?

Agenda

• Do Now• Introduce Deserts• Desert Video• Talk about paper

Deserts

Deserts are found on every continent, usually found on the leeward (downwind) side of mountain ranges

Brief description

• Do on your own

Climate (Precipitation and Temperature)

• Deserts are defined by their extremely low precipitation, less than 16 in a year

• Deserts can exist in a wide range of temperatures (there are deserts in the Arctic and on Antarctica), but most are quite warm

• There is usually a huge swing in temperatures from the daytime to the night in deserts

Soil

• The soil in deserts is very low in organic content, usually high in salts

• The soil is also mostly made up of sand and rocks, as smaller particles get blown away by winds without vegetation to hold them down

• Bad for plants

Plant Life

• Cactti, succulent plants, bushes, clumps of grasses

• No trees

Plant Adaptations• Plants are highly efficient at

acquiring, using, and storing water

• Thick waxy layer (cuticle) to prevent water loss, small leaves, CAM photosynthesis,

• Spines and thorns to protect from water-stealing animals

• Huge roots to take advantage of rare rainfall

Seasonal Variation• Is low in most deserts,

other than cold ones. Some have periods where the rare rains are more likely

• The sporadic rainfalls are the important source of climatic variation, life has evolved to take advantage of brief wet spells

Limiting Factors and Adaptations

• On your own (easy)

Other Physical Factors

• Oases or exotic rivers sometimes exist in deserts, and are obviously a magnet for wildlife

• When rainfall does occur, it is often heavy, and flash floods spring up in normally dry channels called arroyos

Deserts continued

Please Do Now: Fill in the limiting factors section for the desert

Biodiversity and Productivity

• Productivity is very low ( 3), because of a lack of water

• Surprisingly, biodiversity in deserts is not as low as you would expect given the low productivity, but still pretty sparse; call it below average diversity

Succession

• Competition is pretty low in the desert compared to other ecosystems, so succession is not very obvious

• Creosote bushes, and other shrubs with slow growth, k-select tendencies are the climax community

Keystone Species

• Cacti act like the “trees” of the ecosystem in some deserts, providing a microhabitat for all sorts of organisms

Video time

We will discuss after video• Migrations, symbioses,

mating, conservation

You look for during the video• Trophic pyramid, example

organisms, limiting factors and adaptations, famous examples

Aim: Deserts continued

Please Do Now: Why do you think that reptiles like snakes and lizards are so

common in the desert, while amphibians are so rare?

Migrations

• With low productivity, the larger animals that do live in the desert have to cover huge ranges to find enough food, but large scale migrations are uncommon since population densities are so low

Mating Systems

• Lots of life emerges after the rare sudden rain, and does most of their life cycle in this time, which lends itself to promiscuous mating

Symbioses

• Commensalism: young creosote bushes, often the dominant vegetation, need the shade of larger established bushes to survive to maturity

• Creosote bushes and cacti are used by all kinds of animals for nesting sites

Conservation

• Historically, deserts have been well preserved due to their low value to humans

• Solar energy farms, as well as oil and mineral extraction are now competing with the conservation of deserts as wild spaces

Vocab

• Xeric: having to do with deserts• Xerophyte: a desert plant• Succulent: plant that stores water in leaves• Xerocole, an animal that can go extended

periods without water