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Ecosystems Hot arid and semi-arid environments What is an ecosystem? Any unit which involves the interactions in a given area, of organisms with the physical environment; so that a flow of energy leads to an exchange of the materials between living and nonliving parts of the system, can be any size from cow pat to TRF Or in simple terms The living parts (plants and animals) in a given area interacting with their environment (soil, climate,) What are the climatic conditions to which the living parts of Hot arid ecosystems have to adapt? Low and unpredictable rainfall Low humidity Dry winds High summer temperatures How do the soils limit plant life? They are deficient in humus Lack essential plant nutrients (N and Ph) Have a low water holding capacity May have hard pans (solidified deposits of calcium carbonate) due to evaporation Have a high salt concentration What is the productivity of the ecosystem? (amount of new plant tissue produced) Net primary productivity is very low 30 -200 g m2 per year (rainforests = 1800g m2 per year. Desert food webs Very complex as most animals are generalists Few secondary and tertiary carnivores Most higher level animals are omnivores Biomass Very low Food chains relatively short with just 2 or 3 trophic levels Soils = Aridsols Little leaching (loss of nutrients by down-washing) Minerals ions therefore accumulate Causing high salinity or alkalinity Low biomass means organic content is low Two types of Aridisols Solonetz = soil with a sodium carbonate horizon Solonchaks soils with saline horizon Plant and Animal Adaptations Necessary in order to survive Few species have been able to adapt Endemicism = outcome (only found in one area e.g. 200 plant species in Mojave desert) Little biodiversity Plants Xerophytes Plants which have adapted their structure to survive drought Include Succulents (cacti) Phreatophytes (long tap roots) 1. Behavioural adaptations Dormancy for long periods become active only when water available Annuals – drought evading. Germinate, after rain and complete the flower, reproduction, seed cycle very quickly Prickly pear Prickly pear Cactus Stores water in its body Waxy skin to prevent transpiration loss Spines = modified leaves as well as protection against animals Found Africa, Australia, Asia europe Joshua Tree Rare type of Yucca Native to Mojave Leaves are xerophytic – – Needle shape to avoid water loss – Leaf cells store water – Covered with thick waxy cuticle to reduce transpiration loss Creosote bush Found Sw USA Adaptations = – Long lateral tap roots (absorbs distant soil water) – Can extract soil moisture unavailable to other species – High surface to volume ratio optimises rate of heat loss and moisture retention – Stomata on leaves close during the day Creosote bush Tamarisk Phreatophyte (Long roots extending to water table) Salt tolerant Native to North Africa Desert annuals E.g. Desert verbena or desert paintbrush found in SW USA Germinate quickly after heavy rains complete their life cycles very quickly seeds remain dormant unitl next rains Desert paintbrush Desert verbena Halophytes These plants are adapted to survive where there are high salt concentrations (toxic to other species) E.g. salt bush survives on salt pans of USa southwest Desert animals Need to adapt to: – Extremes of temperature – Lack of water Physiological adaptations and behavioural Physiological adaptations Such as changes to body shape to dissipate heat, colouration or conserving moisture Fennec Fox has large ears (to lose heat) and large eyes (for nocturnal hunting) – native of north Africa JACK RABBIT usa circulates blood through ears Coloration Pale fur, scales or feathers to reduce heat absorption i.e. desert species will be paler than similar species elsewhere Obtaining water from food E.g. Turkey vultures and tortoises get all the water they need in this way Excreting wastes as uric acid therefore losing little water this way Common to birds and reptiles Kangaroo rats Recycling their own urine and have special nasal cavities to reduce water loss when breathing Behavioural adaptations Migration during the hottest season (humming birds) Estivation during hottest season ( a kind of hibernation) round tailed ground squirrel) Being active when it is cool Crepuscular – being active at dawn and dusk – rattle snakes and gila monsters (lizards) Nocturnal – bats, most rodents, and larger animals – they often burrow beneath the surface animal adaptations Task Complete page 152 Q1,2 and 3
