2.6 Ecosystem Changes

1. 2.6 Ecosystem Changes

2. Population Growth • Population: a group the same species that live in the same place at the same time • Resources: food, water, shelter, space and mates • In theory populations can grow to an infinite size, but they are limited by resources • This causes individuals to compete for resources (remember intraspecific and interspecific competition!).

3. Factors that Control Populations • There are 4 main factors controlling population sizes: • Natality- births increase the population • Mortality - deaths decrease the population • Immigration - movement of individuals into an area increases the population • Emigration - movement of individuals out of an area decreases the population

4. Carrying Capacity • Carrying capacity: maximum number of individuals of a species that can be sustained indefinitely in a given space • No population can grow indefinitely! Resources = Limited!!

5. Limiting Factors of Populations • Factors (biotic or abiotic) which prevent population numbers from growing too large and overrunning an ecosystem. • Example: • Disease/ parasites • disasters • hunting & predation • competition for resources • (food, oxygen, nutrients)

6. Patterns of Population Growth • “J” population growth curve • Exponential growth = starts out slow and then proceeds faster and faster • Occurs when a population has few resource limitations • Sudden collapse ('diebacks')

7. Patterns of Population Growth • “S” growth curve (S for sigmoid) • Initially shows exponential growth then levels off at the carrying capacity. • Occurs when a population has limited resources. • Results in stable population

8. J Curve vs. S Curve

9. Population Dynamics • A look at the factors that tend to increase or decrease the size of a population • The population size is determined by the interplay of biotic potential and environmental resistance. • Biotic potential- growth rate with unlimited resources • Environmental resistance - all the factors acting jointly to limit population growth

10. Biotic Potential vs. Environmental Resistance Biotic potential (Growth Factors) Environmental resistance (Decrease Factors) • Favorable light, temperature • High reproductive rate • Adequate food supply • Ability to migrate habitats • Ability to adapt to environmental change • Too much or too little light and temperature • Low reproductive rate • Inadequate food supply • Inability to migrate habitats • Inability to adapt to environmental change

11. Biotic Potential vs. Environmental Resistance

12. Reproductive Strategies r Unstable environment, K Stable environment, density • Small size • Many offspring are produced • Early maturity • Short life span • Each individual reproduces once • Type III survivorship curve • Large size • Few offspring produced • Late maturity (long parental care) • Long life span • Individuals reproduce more than once • Type I or II survivorship curve

13. Survivorship Curves • Type I - high survival rate of the young, live most of their expected life span and die in old age. (ex. Humans) • Type II - relatively constant death rate, could be due to hunting or diseases. (ex. coral, squirrels, honey bees and many reptiles) • Type III - have many young, most of which die very early in their life. (ex. plants, oysters and sea urchins).

14. Survivorship Curves

15. Pop Quiz • Which type of survivorship curve does the cheetah have? • What does parental care have to do with the shape of these curves? • If you drew separate survivorship curves for female and male cheetahs, what would they look like? • What do you think the survivorship curve would be for a white-tailed deer population?

16. Density Dependent Factors • Density dependent factors • Depend on the size of the population • Effects of the factors increase as the population grows • Act as negative feedback • Tend to be biotic • Two categories: • Internal factors = Within a single species • limited resources • reduced fertility rates • External factors = between species • populations of predators or prey • diseases spread more easily in densely-populated areas

17. Snowshoe Hare and Canada Lynx

18. Density Independent Factors • Do NOT depend on the size of the population • Tend to be abiotic • Effect the population regardless of its size • Examples: • 1. Weather • 2. Earthquakes • 3. Floods • 4. Fires • R-strategists are most affected by these factors

19. Ecological Succession: Change over Time • Two Types of Succession • Primary succession - An ecosystem starts from bare rock • Secondary succession – Ecosystem is built from a previous ecosystem • Starts with soil

20. Important Terms • Sere:A set of stages of changes in an ecosystem. • A snapshot of ecosystem • Pioneer organisms: First species that begin to populate a sere, typically r-strategists. • Ex. Weeds, lichens • Climax community: Populations of organisms living together in a sere where all species are in balance. • Ex. A mature forest, many K-strategists

21. Pioneer Species

22. Primary Succession • No soil in a terrestrial system • No bottom sediment in an aquatic system • Takes hundreds to thousands of years • Need to build up soils/sediments to provide necessary nutrients

23. Primary succession will occur after a volcanic eruption

24. Primary succession occurs after a glacier retreats Image source: http://www.callipygia600.com/

25. Primary succession occurs after a glacier retreats

26. Primary succession occurs after a glacier retreats

27. Glacier Bay, Alaska

28. Primary Ecological Succession Lichens and mosses Exposed rocks Balsam fir, paper birch, and white spruce forest community Jack pine, black spruce, and aspen Heath mat Small herbs and shrubs Time

29. Secondary Succession • Begins with soil from previous ecosystem • Ecosystem has been • Disturbed, Removed, or Destroyed • Abandoned farms • Burned forests • Deforestation • A huge storm

30. SecondarySuccession Mature oak and hickory forest Young pine forest with developing understory of oak and hickory trees Shrubs and small pine seedlings Perennial weeds and grasses Annual weeds Time

32. Secondary Ecological Succession in Yellowstone Following the 1998 Fire

33. Conditions during succession • Early Stages Gross Productivity is Low • Not many producers • Later Stages Gross Productivity is High • Climax Community