Chapter 5 Population Ecology

1. Chapter 5Population Ecology

2. Populations Growth • Population Growth • Three factors can affect population size: • number of births • the number of deaths • the number of individuals that enter or leave the population. * Simply put, a population will increase or decrease in size depending on how many individuals are added to it or removed from it

3. Immigration & Emmigration • Immigration • the movement of individuals into an area, is another factor that can cause a population to grow. • Emigration • the movement of individuals out of an area, can cause a population to decrease in size.

5. In 1911, 25 reindeer were introduced on Saint Paul Island in the Pribolofs off Alaska. The population grew rapidly and nearly exponentially until about 1938, when there were over 2000 animals on the 41-square-mile island. The reindeer badly overgrazed their food supply (primarily lichens) and the population “crashed.” Only eight animals could be found in 1950. A similar sequence of events occurred on Saint Matthew Island from 1944 through 1966. [After Krebs (1972) after V. B. Scheffer (1951). The Rise and Fall of a Reindeer Herd. Science 73: 356–362.]

6. Exponential GrowthPopulations growing without restriction! • If a population has abundant space and food, and is protected from predators and disease, then organisms in that population will multiply and the population size will increase.

7. Exponential Growth Exponential growth occurs when the individuals in a population reproduce at a constant rate. Under ideal conditions with unlimited resources, a population will grow exponentially.

8. Exponential population growth is described by the simple differential equationdN/dt = rN where,change in number of individuals (dN) per Change in time (dt) = growth rate (rN)

9. Logistic Growth • Logistic growth occurs when a population's growth slows or stops following a period of exponential growth. • As resources become less available, the growth of a population slows or stops. The general, S-shaped curve of this growth pattern, called logistic growth

10. Carrying Capacity The number or the largest number of individuals that a given environment can support.

11. Variations of the Logistic Model • If food becomes scarce, the population will experience an overshoot by becoming larger than the spring carrying capacity and will result in a die-off, or population crash.

12. environmental resistance. : the sum of the environmental factors (such as drought, mineral deficiencies, and competition) that tend to restrict the biotic potential of an organism

13. Population-same species, same place, same time • Characteristics of Populations Three important characteristics of a population • geographic distribution • Density • growth rate

14. Geographic distribution, or range, is a term that describes the area inhabited by a population. Clumped- Most common social, protection, resources Uniform- predator-territoriality Allelopathy Random- less common Resources evenly distributed

15. Population DensityPopulation density is the number of individuals per unit area • . • The population of saguaro cactus in the desert plant community has a low density, whereas other plants in that community have a relatively high density.

16. Factors that Restrict the Size of a Population Limiting Factors of Environmental Resistance

17. Density-Dependent Limiting Factors • The degree of influence depends on the size of the population. • Examples: competition, predation, parasitism, stress caused by crowding, disease • Seldom totally eliminate a population • Some populations are self-controlling in that they have mechanisms to reduce competition – delayed maturation caused by malnutrition, migration, cannibalism.

18. Density-Independent Limiting Factors • The degree of influence is not related to population size. • Examples: pollution, habitat destruction, natural disasters, weather • Usually just reduce the population below the cc. but they have the ability to totally eliminate a population

19. Density Independent Factors Influencing Populations

20. Density Dependent Factors Influencing Populations

21. Types of Species • Generalist • large niches • tolerate wide range of environmental variations • do better during changing environmental conditions • Specialist • narrow niches • more likely to become endangered • do better under consistent environmental conditions

22. r and k strategists • Depending upon the characteristics of the organism, organisms will follow a biotic potential or carrying capacity type reproductive strategy The r-strategists (Type III) • High biotic potential – reproduce very fast • Are adapted to live in a variable climate • Produce many small, quickly maturing offspring = early reproductive maturity • “Opportunistic” organisms The K-strategists (Type I) • Adaptations allow them to maintain population values around the carrying capacity • They live long lives • Reproduce late • Produce few, large, offspring

23. Survivorship Curves k-strategist • Survivorship curves show the distribution of individuals in a population according to age • Humans and most mammals have a Type I survivorship curve because death primarily occurs in the older years. • Birds have a Type II survivorship curve, as death at any age is equally probable. • Trees have a Type III survivorship curve because very few survive the younger years, but after a certain age, individuals are much more likely to survive. • / r-strategist

24. Community Relationships

25. Types of Species • Native species normally live and thrive in a particular ecosystem • Nonnative species are introduced - can be called exotic or alien • Indicator species serve as early warnings of danger to ecosystem- birds & amphibians • Keystone species are considered of most importance in maintaining their ecosystem

27. Identify some of the factors that could cause a change in the number of red crabs onChristmas Island. Predict what would happen to the red crab population as the result of a (1) drought, a (2) hurricane, or the introduction of a (3)predator to the ecosystem.

28. Christmas Island red crabGecarcoidea natalis • The land crab that is endemic to Christmas Island in the Indian Ocean. An estimated that 43.7 million adult red crabs lived on Christmas Island alone. The accidental introduction of the yellow crazy ant is believed to have killed about 10–15 million of these in recent years. • Christmas Island red crabs are well known for their annual mass migration to the sea to lay their eggs in the ocean.

29. Christmas Island Land CrabKeystone Species • Christmas Island's biodiversity - land crabs are a keystone species in the forest ecology: they dig burrows, turn over the soil, and fertilise it with their droppings. • Seedlings that were previously eaten by crabs started to grow and, as a result, changed the structure of the forest. • Weeds also spread into the rainforest because there are no crabs to control them.

30. Factors that Influence Population Size • Density-dependent factors- the size of the population will influence an individual’s probability of survival. • Density-independent factors- the size of the population has no effect on the individual’s probability of survival.

31. Exponential Growth Model • Intrinsic growth rate- under ideal conditions, with unlimited resources, the maximum potential for growth.

32. Resource Patitioning

33. Predation • Predation- the use of one species as a resource by another species. • True predators- kill their prey. • Herbivores- consume plants as prey. • Parasites- live on or in the organism they consume. • Parasitoids- lay eggs inside other organisms.

34. Mutualism • Mutualism- A type of interspecific interaction where both species benefit.

35. Commensalism • Commensalism- a type of relationship in which one species benefits but the other is neither harmed nor helped.

36. Community Ecology • Each species has a particular ecological niche or role that it plays in an ecosystem.

37. Competitive Exclusion Principle • Two species that have exactly the same requirements cannot coexist in exactly the same habitat.

38. r-Selected Species Cockroach Dandelion Many small offspring Little or no parental care and protection of offspring Early reproductive age Most offspring die before reaching reproductive age Small adults Adapted to unstable climate and environmental conditions High population growth rate (r) Population size fluctuates wildly above and below carrying capacity (K) Generalist niche Low ability to compete Early successional species

39. K-Selected Species Saguaro Elephant Fewer, larger offspring High parental care and protection of offspring Later reproductive age Most offspring survive to reproductive age Larger adults Adapted to stable climate and environmental conditions Lower population growth rate (r) Population size fairly stable and usually close to carrying capacity (K) Specialist niche High ability to compete Late successional species

40. The Giant Panda: Specialized and Endangered • Classic k-strategist = specialist • Feeds exclusively on bamboo (1/3 of body weight) • Habitat fragmentation has created “habitat islands” of bamboo in southwestern China due to human encroachment. • 12 protected reserves in China.

41. Why Are Panda Faced With Extinction? • Illegal poaching (pelt brings in $40,000-60,000). • Only one cub per female survives each year. • Gestation period = 22 months • Picky about mates. Find each other through scent, become isolated due to habitat fragmentation. • Habitat islands interrupt natural migration to adjacent areas when bamboo population crashes in local areas. • Approximately 700 panda left between zoos and the wild.

42. What Are Indicator Species? • Indicator species serve as early warnings of damage to a community. • Birds and butterflies are migratory and are excellent indicators of the environment. They do not return to areas along their migratory routes where deforestation has occurred or where broad spectrum pesticides have been applied. • Amphibians are also a universal indicator of environmental degradation as they respire through their skin.

43. Indicator Species • As indicator species, amphibians may be sending us an important message about the health of the global environment. • They don’t need us, but we and other species need them. Golden toads – once prevalent in Costa Rica’s cloud forest have disappeared.

44. Indicator Species in New England Why are species in trouble HIPPCO

45. What Are Keystone Species? • A keystone species holds a community together, when it disappears, so does the biological community. Elimination of a keystone species dramatically alters the structure and function of a community.

46. American Alligator – a Keystone Species • Largest North American reptile; only humans are their predator. • Hunted nearly to extinction for exotic meat, and leather to make shoes and pocketbooks, and for sport.

47. Ecological Niche of American Alligator • Dig gator holes that collect freshwater during the dry season which serve as refuges for aquatic life, and supply freshwater and food for many animals.

48. Ecological Niche of American Alligator • Alligator nesting mounds serve as nesting and feeding sites for herons and egrets

49. Ecological Niche of American Alligator • Alligator eat large numbers of predatory gar fish and help maintain healthy numbers of game fish such as bass and bream.

50. Ecological Niche of American Alligator • As alligators move from gator holes to nesting sites, they keep areas of open water free of invading vegetation. This helps to maintain healthy ecosystems with flowing water.