Ecosystems

1. Ecosystems Hot arid and semi-arid environments

2. 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

3. Or in simple terms • The living parts (plants and animals) in a given area interacting with their environment (soil, climate,)

4. 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

5. 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

6. 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.

7. Desert food webs • Very complex as most animals are generalists • Few secondary and tertiary carnivores • Most higher level animals are omnivores

8. Biomass • Very low • Food chains relatively short with just 2 or 3 trophic levels

9. 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

10. Two types of Aridisols • Solonetz = soil with a sodium carbonate horizon • Solonchakssoils with saline horizon

11. 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

12. Plants • Xerophytes Plants which have adapted their structure to survive drought Include • Succulents (cacti) • Phreatophytes (long tap roots)

13. 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

14. Prickly pear

15. 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

16. 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

18. 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

19. Creosote bush

20. Tamarisk • Phreatophyte (Long roots extending to water table) • Salt tolerant • Native to North Africa

22. 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

24. Desert paintbrush

25. Desert verbena

28. 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

31. Desert animals • Need to adapt to: • Extremes of temperature • Lack of water • Physiological and behavioural adaptations

32. Physiological adaptations • Such as changes to body shape to dissipate heat, colouration or conserving moisture

33. Fennec Fox has large ears (to lose heat) and large eyes (for nocturnal hunting) – native of north Africa

34. JACK RABBIT usa • circulates blood through ears

35. Coloration • Pale fur, scales or feathers to reduce heat absorption i.e. desert species will be paler than similar species elsewhere

36. Obtaining water from food • E.g. Turkey vultures and tortoises get all the water they need in this way

37. Excreting wastes as uric acid therefore losing little water this way • Common to birds and reptiles

38. Kangaroo rats • Recycling their own urine and have special nasal cavities to reduce water loss when breathing

39. Behavioural adaptations • Migration during the hottest season (humming birds) • Estivation during hottest season ( a kind of hibernation) round tailed ground squirrel)

40. 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

41. Task • Complete page 152 Q1,2 and 3