Environmental Issues Ecology
What Factors Affect Population Growth? • Millions of red crabs live in Christmas Island in the Indian Ocean. Each year, the entire adult crab population migrates from forest to sea to breed, making daily life a bit tricky for human residents! What factors could influence the growth or decline of the red crab’s population size?
Penguins! • What factors could affect the size of penguin populations in Antarctica? • http://video.nationalgeographic.com/video/kids/animals-pets-kids/birds-kids/penguin-emperor-parenting-kids/ • http://dsc.discovery.com/tv-shows/frozen-planet/videos/criminal-penguin.htm
A Plague of Rabbits • In 1859, an Australian farmer released 24 wild European rabbits from England on his ranch. “A few rabbits”, he said, “could do little harm and might provide a touch of home in addition to a spot of hunting.” • Seven years later, he and his friends shot 14,253 rabbits. In 10 years, more than 2 million rabbits were hunted on that farm alone! • That “touch of home” was soon covering the countryside like a great gray blanket. The millions of rabbits devoured native plants and pushed native animals to near extinction. These cute, fuzzy creatures weren’t a problem in England. Why did they turn into a plague in Australia?
Two Different Problems • In the 1950s, a fish farmer released a few aquarium plants (called Hydrilla) into a canal, thinking it would be harmless. • Today, Hydrilla have overtaken waterways all over Florida. Stems tangle boats and the plant has completely taken over habitats. Native plants and animals are disappearing. • Fishermen in New England face a different problem. In recent years, despite hard work and new equipment, their catch has dropped dramatically. • The cod catch in one recent year was 3,048 metric tons. The cod catch in 1982 was 57,200 metric tons, 19 times higher! Where did all the fish go?
How do Ecologists Study Populations? • Geographic Range=the area inhabited by a population. • A population’s range can vary enormously in size, depending on the species. North Carolina Black Bear Population Range: 1971—About 4,000 bears occupied approximately 2.5 million acres 2008—About 11,000 bears lived on almost 10 million acres
How do Ecologists Study Populations? Population Density=number of individuals per unit area. • Populations of different species often have very different densities, even in the same environment.
Population Distribution • Population Distribution=how individuals in a population are spaced out.
Population Growth Rates • Population Growth=Birth Rate-Death Rate • A population’s growth rate determines whether the size of the population increases, decreases or stays the same. • Hydrilla populations tend to stay the same size over time in its native range in Indonesia. • The Hydrillapopulation in Florida, by contrast, has a high growth rate. What factors are influencing The growth rate of Hydrilla?
Population Growth-Migration Births + Immigration = Population ↑ • Immigration vs. Emigration • A population may grow if individuals move into its range (Immigration). • A population may decrease if individuals move out of its range (Emigration). Deaths + Emigration = Population ↓
Exponential Growth • If you provide a population with all the food and space it needs, protect it from predators and disease, and remove its waste products, what will happen? How many bacteria will there be in 6 more days? (1.0 X 1013) That is 10,000,000,000,000!
Exponential Growth The size of each generation is larger than the generation before it. The larger a population gets, the faster it grows! This is called exponential growth. In ideal conditions, all species will exhibit exponential growth, resulting in a J-shaped growth curve.
Gypsy Moth Population • Sometimes, when an organism such as the European rabbit or Hydrilla are introduced to a new environment, its population grows exponentially for a time. • When a few gypsy moths were accidentally released from a laboratory near Boston, within a few years, they had spread across the northeastern U.S. • In peak years, they devoured the leaves of thousands of acres of forest. In some places, they formed a living blanket that covered the ground, sidewalks and cars!
Gypsy Moth • One scientist said about the gypsy moth, "Where I live in Pennsylvania, it's too late to slow the moths' spread because they already are prevalent across the entire state. It's so bad here that, at certain times, if you stand in the forest and listen, it sounds like it's raining, but what's raining is their excrement."
Logistic Growth • Natural populations don’t grow exponentially for long. Sooner or later, something stops exponential growth. • Phase 1: Exponential growth • Phase 2: Growth slows down • Phase 3: Growth stops • This produces an “S-shaped” curve • (NOTE: This does not mean the species dies out—only that the growth of the population stops.)
Carrying Capacity • When the birth rate and death rate are the same and when immigration equals emigration, population growth stops. • It may still rise and fall somewhat, but the ups and downs average out at its’ carrying capacity. • Carrying Capacity is the maximum number of individuals that a particular environment can support for an extended period of time. What is the carrying capacity of deer on WallaWalla Island?
Limiting Factors • A limiting factor is a factor that limits the growth of a population. They determine the carrying capacity of an environment for a particular species. These may include: • Competition • Predation • Parasitism & Disease • Natural disasters • Severe weather
Density-Dependent Limiting Factors • Density-dependent Limiting Factors operate strongly only when the population density reaches a certain level. • These include: • Competition • Predation and Herbivory • Parasitism • Disease • Stress from overcrowding The relationship between Lynx and Snowshoe hare illustrates how predation can affect population growth.
Density-Independent Growth Factors • Density-Independent Limiting Factors affect all populations—no matter how big or small they are. • These include: • Severe weather events such as hurricanes or drought • Floods • Wildfires • Natural disasters
What would be limiting factors for Emperor Penguins? • What factors would influence the size of Emperor Penguin populations?
Keystone Species • Sometimes changes in the population of a single species, called a keystone species can cause dramatic changes in the structure of a community. Sea otters are a keystone species on the northern California coastlines and their favorite food is sea urchins. Sea urchins are herbivores whose favorite food is kelp, giant algae that grow in undersea “forests”. Sea otters were nearly eliminated due to hunting. When that happened, however, sea urchin populations skyrocketed and they ate all the kelp. Without kelp to provide habitat, many other animals disappeared. When otters became protected, the ecosystem slowly recovered.
Organisms in Antarctica • Which of the following is the keystone species of Antarctica? Krill Skua Chinstrap Penguin Adelie Penguin Leopard Seal Emperor Penguin
Introduction to Antarctica Antarctic Ecosystems
Antarctic Ecosystem is Changing • In the last century, air temperatures in Antarctica have risen an average of 3oC. • The most significant effect of this is a shift in the population of different species of penguins. • Adelie Penguins have lived on the Antarctic Peninsula for 600 years, yet their population is declining. They depend on sea ice for survival. • Chinstrap Penguins, which prefer open water, are increasing dramatically.