Population Ecology and Human Impacts on Ecosystems

1. Standard 3Interdependence of Living Systems & the EnvironmentUnit 8 – Population Ecology & Human Impacts on Ecosystems

2. Objectives • B3.4A: Describe ecosystem stability. Understand that if a disaster such as flood or fire occurs, the damaged ecosystem is likely to recover in stages of succession that eventually result in a system similar to the original one. • B3.4C: Examine the negative impact of human activities. • B3.5B: Explain the influences that affect population growth

3. Questions • How much longer will petroleum resources last? • What effect is the population having on the water system? • What is the effect of recycling paper and aluminum cans?

4. Estimated world population at various dates, in thousands Human Population

5. In Closed Populations, Growth Rate is Determined by the Difference Between Birth and Death Rates r = birth rate – death rate

6. Population Growth Reflects the Balance Between Birth and Death Rates For example, Mexico’s population has grown explosively even though its birth rate has declined

7. Estimated rates of US population growth with or without immigration. Immigration and Emigration Can Strongly Effect Population Dynamics

8. A Population’s Age Structure Determines Its Potential for Growth Populations with a pyramid-shaped age structure will grow explosively. Populations with a rectangular age structure will grow much slower. Generally, human populations in the developed world are “rectangular” and those of developing nations are “pyramidal.”

9. The World’s Human Population Has Grown Explosively in the Past 200 Years Continued rapid human population growth is one of the greatest strains on the health of ecosystems and humanity.

10. Human Population Growth Is Unevenly Distributed The recent increase in human population in the developing world is due primarily to decreased death rate, not increased birth rate.

11. Human Population Density Varies Widely

12. The Carrying Capacity for Human Populations Is Unknown Although a precise figure isn’t known, it’s clear that carrying capacity is influenced by technology.

13. World Population Growth is Slowing The major factor is declining fertility rates.

14. World Population Growth is Slowing Population structure of Kenya in 2000 and projections for 2050.

16. BIOMAGNIFICATION • Biomagnification= a substance gets more concentrated as it passes through the food chain. Example – DDT • The concentration effect occurs because DDT is metabolized and excreted much more slowly than the nutrients that are passed from one trophic level to the next. So DDT accumulates in the bodies (especially in fat). Thus most of the DDT ingested as part of gross production is still present in the net production that remains at that trophic level.

17. Biomagnification is the bioaccumulation of a substance up the food chain by transfer of residues of the substance in smaller organisms that are food for larger organisms in the chain. It generally refers to the sequence of processes that results in higher concentrations in organisms at higher levels in the food chain (at higher trophic levels). These processes result in an organism having higher concentrations of a substance than is present in the organism’s food. Biomagnification (00:59)

18. Succession • Succession = gradual change of a site into a different ecosystem • Pond → Swamp→ Meadow → Forest Stages of Succession (01:14)

19. Primary Succession at Glacier Bay, Alaska Factors That Influence Succession (05:46) A climax community is the stable community at the final stage of succession.

20. Sand Dune Succession • Where a series of dunes has formed at the back of a beach, the youngest dunes will be closest to the shore and the oldest furthest away. • This is one of the few examples where all the stages of a succession can often be clearly seen in one place. Pioneer Stage – Foredunes Yellow (White) Dune Stage Conifer Plantations Dune Building

21. Model of Dry Dune Succession Dunes' stages can be connected, but they don't have to be. A single dune can go through all the stages without having another dune next to it. However, most of the dunes are connected to other dunes often in other stages of Succession. New dunes are constantly being formed near the beach, as seen above, a dune has just started Succession, although it has been growing for many years.

22. Nature’s Complexity • Hierarchical Organization • Landscapes • Ecosystems • Communities • Species • Populations • Individuals • Organ systems • Organs • Organ tissues • Cells • Cell organelles • Molecules LESS understanding = Ecologist’s realm MORE understanding

23. Population Ecology • Scientific study of individual populations and their interaction with, or response to, the environment. • Population = all the individuals within a species • Carrying Capacity = the population or # of individuals an ecosystem can hold/sustain • Sustainability= the ability of an ecosystem to support a population indefinitely Population size Time Learning Ecological Terms (07:23)

24. Populations – Communities - Ecosystems • Organisms of one species form a population. • Populations of different organisms interact to form communities. • Living communities and the nonliving factors that interact with them form ecosystems. • List all components (biotic & abiotic) in a pond ecosystem Population and Community (02:19)

25. Levels of Ecological Investigation

26. Population Ecology A population is a group of individuals of the same species that occupy a specified region at a specified time. Key questions of population ecology include: What is the size of a population? What is the potential for growth in the population? What form will growth take?

27. Community Ecology Community ecology examines the question of how populations interact. Questions include: What are the types of species and their numbers within a community (i.e. community structure)? Are there especially critical species for maintenance of the community? What is the relationship (predator, prey, parasite) between species within the community?

28. Community Ecology • The study of groups of species that live together in a particular area or habitat. • Habitat = place where a species lives (human habitat = house) Habitats (00:38) Populations, Habitats, and Niches (03:30) Interspecific Interactions + / o Commensalism + / + Mutualism + / - Parasitism Parasitoidism Herbivory + / - - Predation - / - Competition Types of Interactions Within Ecosystems (04:35)

29. Interdependency • Two organisms can be mutually beneficial and that can lead to interdependency. • Interdependency = mutuality: a reciprocal relation between interdependent entities (objects or individuals or groups). • Apples & Honey Bees

30. The oxpecker gets food (ticks and insects disturbed in the grass) and a safe haven from the rhinoceros, and the rhinoceros has parasites (ticks) removed. Mutualism Mutualism occurs when species interact in a mutually beneficial manner. Relationships Between Populations: Symbiotic (02:30)

31. Mutualism Mycorrhizal fungi (threads) covering aspen roots: fungi aid in water and nutrient absorption by the aspen and the aspen provides sugars and other food molecules to the fungi.

32. Parasites • A parasite is an organism that lives in or on the living tissue of a host organism at the expense of that host. The biological interaction between the host and the parasite is called parasitism. • A parasite is an animal or plant that lives in or on a host (another animal or plant); it obtains nourishment from the host without benefiting or killing the host Tapeworm Whipworm

33. Parasites • Almost everyone has parasites. It’s simply a fact of life. Even Dr. Oz, the now famous Oprah Winfrey guest says..."ninety percent of humans will have a problem with parasites in their lifetime." Parasites are not just something that other people get – a malady reserved for citizens of developing countries. Everywhere we go, during just about everything we do, North Americans are vulnerable to parasitic infestation. • The World Health Organization (WHO) classifies parasites as among the six most dangerous diseases that infect humans. Parasites outrank cancer as the number one global killer, and account for many of the digestive woes from which people suffer. Hookworm Roundworm Mosquito Parasitic Worms of the Animal Kingdom (05:06)

34. Parasites • Homework - Diagram the stages of the life cycle for a human disease-causing organism.

35. Biodiversity There are many measures of biodiversity. Considering species diversity, more diverse communities tend to be more productive. The role of diversity in community stability is less clear.

36. Biodiversity Remember, however, that this is one set of communities.

37. Why Worry About the Relationship Between Biodiversity and Community Stability? Because this understanding is essential for knowing how many species and of what types can be lost before a community collapses. Connected Systems: Biodiversity, Ecosystems, and Ecology

38. Biodiversity Varies Naturally There is a trend towards more species in warmer, wetter areas and fewer in colder and drier areas. Why Should We Care? (04:22) Numbers of bird species occupying areas of North America.

39. Science (2005) 309:90 We really don’t have a satisfying answer to this fundamental question.

40. Biodiversity hotspots for tropical rain forest and chaparral ecosystems. There are Biodiversity “Hotspots” Less than 1% of Earth’s surface supports 20% of known plant species and probably a greater portion of animal species. Biodiversity hotspots are significant for conservation plans.

41. Biodiversity is Being Lost Rapidly Through Extinction How rapid is the current rate of extinction? The number’s hard to pin down, but generally accepted estimates put it at 10-100 times the rate before extensive human–induced environmental modifications. For example, in the U.S. ~ 225 vascular plant species have become extinct in the past 50 years and about 650 of the remaining 20,000 species are threatened.

42. Community Ecology • Predator-Prey Relationship = 2 species have a relationship where the population of one affects the population of the other one • The predators -- eat the other -- the prey • Such pairs exist throughout nature: • lions and gazelles, • birds and insects, • pandas and bamboo, • Venus fly traps and flies • http://www.accessexcellence.org/AE/AEPC/WWC/1991/predator.html Predator-Prey Relationships: The Example of the Bobcat and Rabbit (01:44)

43. Predator-Prey

44. Equilibrium • As the number of carnivores in a community increases, they eat more and more of the herbivores, decreasing the herbivore population. It then becomes harder and harder for the carnivores to find herbivores to eat, and the population of carnivores decreases. In this way, the carnivores and herbivores stay in a relatively stable equilibrium, each limiting the other's population. A similar equilibrium exists between plants and plant-eaters.

45. Predator and prey, host and parasite are locked in a duel to outwit their opponent through adaptations. Predation, Parasitism and Coevolution Predation (consuming another organism) and parasitism (feeding upon a host organism without causing its immediate death) drive an evolutionary arms race. Predator and prey interactions drive coevolution – coupled adaptive changes in interacting species.

46. Reproductive Strategies • Describe different reproductive strategies employed by various organisms and explain their advantages and disadvantages. • Although every organism struggles to survive, individual survival is not enough to ensure continuation of the species.  Individuals must reproduce. • Scientists have identified two strategies for leaving living descendants. These strategies are called the r-strategy and the k-strategy.  Some organisms, animals and plants, use one strategy or the other: some seem to tend towards one but are closer to a sort of mid-point. Let's compare these strategies. • Hint - Remember that R stands for Rapid so that you will remember which strategy is which.  R-Selected parents rapidly produce many descendents, but do not provide care for them.

48. Reproductive Strategies • We see that r-selected organisms have many babies, but most of these youngsters never become adults. Frogs are a good example of r-selected organisms. Frogs lay many eggs and leave them in the water to hatch into tadpoles. Some of the eggs get eaten, and many of the little tadpoles are eaten, too, by dragon-fly larvae and fishes and fishing birds. When the tadpoles become frogs, many animals are waiting on shore to eat them: raccoons, foxes, snakes, cats, and many other small predators. If one frog from a hundred eggs lives to be a parent, his/her survival is really outstanding. But frogs go on because they lay so many eggs.

49. Reproductive Strategies • Elephants are examples of K-selectedanimals. Female elephants have babies about three years apart, and they have only one each time. The whole group looks after the youngsters, and protects them through childhood and adolescence. By reproducing at a rate that holds their numbers close to constant, elephants are able to survive in stable ecosystems. Because they ensure the survival of a good percentage of their young, elephants do not need to produce many elephant babies

50. Reproductive Strategies - Farm • Cattle - Heifers become sexually mature cows at between 15 and 27 months; bulls are mature at 1 year. Gestation is about 9 months. Cows can't be milked unless they have given birth, so each female is expected to produce at least 1 living calf every year. In the U.S. beef cattle calves are usually born in the spring; they stay with their mothers until weaned and are sold off in the fall. Cows have a calf in the spring and are breed again in early summer when the calf is only about 3-4 months old. • Swine - Sexual maturity of a gilt can be reached between 8 and 10 months of age. Sows usually have litters of from 1 to 15 young, generally 8 being average. Females are extremely protective of their young. Gestation is 3 months, 3 weeks, 3 days. Piglets are weaned after an average of 4-5 weeks. The sows will recondition and get rebreed to have their second litter for the year. • Mouse - Sexually mature at 4-7 weeks (both males and females) with a life expectancy of 1-3 years. Cycle of heats every 4-5 days, continuing all year round with a gestation period of19-21 days. Average size of litter is 4-14 (even more), averaging 12 babies which they nurse for approximately 3-3.5 weeks. They are weaned at males 3,5 weeks, females may be weaned at 4 weeks. They then separate to single sex groups at 3.5 weeks and are ready to leave for new homes at 1 month of age. Females experience a resting period between matings of at least 2 weeks, preferably over 1 month between weaning of one litter and mating for another.