2.6 Ecosystem Changes

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!).

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

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!!

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)

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')

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

J Curve vs. S Curve

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

Biotic Potential vs. Environmental Resistance (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

Biotic Potential vs. Environmental Resistance

Reproductive Strategies K Stable environment, density r Unstable environment, 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

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).

Survivorship Curves

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?

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

Snowshoe Hare and Canada Lynx Figure 5.18: This graph represents the population cycles for the snowshoe hare and the Canadian lynx. At one time, scientists believed these curves provided evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—through predation by lynx and other predators—and bottom-up population control, in which changes in the availability of the food supply for hares help to determine their population size, which in turn helps to determine the lynx population size. (Data from D. A. MacLulich)

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

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

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

Pioneer Species

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

Primary succession will occur after a volcanic eruption

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

Primary succession occurs after a glacier retreats

Primary succession occurs after a glacier retreats

Glacier Bay, Alaska

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

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

Mature oak and hickory forest Secondary Succession 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

Secondary Ecological Succession in Yellowstone Following the 1998 Fire Figure 5.21: These young lodgepole pines growing around standing dead trees after a 1998 forest fire in Yellowstone National Park are an example of secondary ecological succession.

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