Biodiversity, Species Interactions, and Population Control

1. Biodiversity, Species Interactions, and Population Control Chapter 5

2. Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction? • Habitat • Hunted: early 1900s • Partial recovery • Why care about sea otters? • Ethics • Keystone species • Tourism dollars

3. Video: Kelp forest (Channel Islands)

4. Purple Sea Urchin

5. Video: Otter feeding

6. Video: Coral spawning

7. Science Focus: Why Should We Care about Kelp Forests? • Kelp forests: biologically diverse marine habitat • Major threats to kelp forests • Sea urchins (male sea otters can eat ~50 sea urchins/ day – equivalent of a 150lb person eating 160 burgers/day) • Pollution from water run-off – pesticides herbicides • Global warming

8. 5-1 How Do Species Interact? • Concept 5-1 Five types of species interactions—competition, predation, parasitism, mutualism, and commensalism—affect the resource use and population sizes of the species in an ecosystem.

9. Species Interact in Five Major Ways • Interspecific Competition – members of 2 or more species interact for limited resources • Predation – member of 1 species feeds directly on another living species • Parasitism – 1 organism feeds on another; causing harm to the host • Mutualism – interaction between 2 species in which both benefit • Commensalism – interaction between 2 species that benefits 1 & causes no harm to the other

10. Most Species Compete with One Another for Certain Resources • Competition – ability of 1 species to be more efficient at finding food or other resources than another species • Competitive exclusion principle – no 2 species can occupy same niche for very long • Both can suffer OR • 1 must either: migrate, change its habits, suffer a population decline, or become extinct Name the species that has out-competed most other species on Earth.

11. Most Consumer Species Feed on Live Organisms of Other Species (1) • Predators may capture prey by • Walking • Swimming • Flying • Pursuit and ambush • Camouflage • Chemical warfare - venom Crazy animal behaviour - Seahorse attacked by Flounder - YouTube Owl Attacks Camera in Slow Motion Made For Spirtaway1 and Mpenziwe And Haifahaifa12 - YouTube

12. Most Consumer Species Feed on Live Organisms of Other Species (2) • Prey may avoid capture by • Camouflage • Chemical warfare - skunks • Warning coloration • Mimicry • Deceptive looks • Deceptive behavior Biologist E.O. Wilson’s 2 rules for coloration: • small & strikingly beautiful – probably poisonous • strikingly beautiful & easy to catch – probably deadly Cephalopod, master of camouflage - YouTube

13. (a) Span worm (b) Wandering leaf insect (c) Bombardier beetle (d) Foul-tasting monarch butterfly (f) Viceroy butterfly mimics monarch butterfly (e) Poison dart frog (g) Hind wings of Io moth resemble eyes of a much larger animal. (h) When touched, snake caterpillar changes shape to look like head of snake. Spicebush caterpillar defense – YouTube Snake Caterpillar - YouTube Stepped Art Fig. 5-2, p. 103

14. Predator and Prey Species Can Drive Each Other’s Evolution • Intense natural selection pressures between predator and prey populations • Predation helps increase biodiversity by promoting natural selection leading to species evolving ability to share limited resources by reducing niche overlap • Coevolution – pred-prey populations interact long enough (100’s – 1000’s of years) that changes in gene pool of 1 leads to changes in the other • Bats and moths An evolutionary arms race (coevolution) - YouTube

15. Coevolution: A Langohrfledermaus Bat Hunting a Moth

16. Some Species Feed off Other Species by Living on or in Them • Parasitism Parasite usually much smaller than host and doesn’t kill them • Parasite-host interaction may lead to coevolution • Malaria parasite evolved methods to stick to blood vessels and counteract host’s immune system

17. Parasitism: Tree with Parasitic Mistletoe, Trout with Blood-Sucking Sea Lampreys Healthy tree on left Tree infested w/ parasitic mistletoe on right Sea Lamprey attached to lake trout from Great Lakes

18. In Some Interactions, Both Species Benefit • Mutualism • Nutrition and protection relationship • Gut inhabitant mutualism • Each species benefits by unintentionally exploiting the other as a result of traits obtained through natural selection

19. Mutualism: Oxpeckers Clean Rhinoceros; Anemones Protect and Feed Clownfish Examples of mutualism. (a) Oxpeckers (or tickbirds) feed on parasitic ticks that infest large, thick-skinned animals such as the endangered black rhinoceros. (b) A clownfish gains protection and food by living among deadly stinging sea anemones and helps protect the anemones from some of their predators. (Oxpeckers and black rhinoceros: Joe McDonald/Tom Stack & Associates; clownfish and sea anemone: Fred Bavendam/Peter Arnold, Inc.)

20. In Some Interactions, One Species Benefits and the Other Is Not Harmed • Commensalism • Epiphytes • Birds nesting in trees

21. Commensalism: Bromiliad Roots on Tree Trunk Without Harming Tree This bromeliad (epiphyte) roots on the trunk of a tree, rather than in soil, without harming or penetrating the tree. It gains access to water, sunlight, & nutrient debris without any harm or benefit to the tree.

22. 5-2 How Can Natural Selection Reduce Competition between Species? • Concept 5-2 Some species develop adaptations that allow them to reduce or avoid competition with other species for resources.

23. Some Species Evolve Ways to Share Resources • Resource partitioning • Reduce niche overlap • Use shared resources at different • Times • Places • Ways

24. Competing Species Can Evolve to Reduce Niche Overlap Competing species can evolve to reduce niche overlap. The top diagram shows the overlapping niches of two competing species. The bottom diagram shows that through natural selection, the niches of the two species become separated and more specialized (narrower) as the species develop adaptations that allow them to avoid or reduce competition for the same resources.

25. Blackburnian Warbler Black-throated Green Warbler Cape May Warbler Bay-breasted Warbler Yellow-rumped Warbler Sharing the wealth: resource partitioning of five species of insect-eating warblers in the spruce forests of the U.S. state of Maine. Each species minimizes competition for food with the others by spending at least half its feeding time in a distinct portion (shaded areas) of the spruce trees, and by consuming different insect species. (After R. H. MacArthur, “Population Ecology of Some Warblers in Northeastern Coniferous Forests,” Ecology 36 (1958): 533–536.) Stepped Art Fig. 5-8, p. 107

26. Specialist Species of Honeycreepers Specialist species of honeycreepers. Evolutionary divergence of honeycreepers into species with specialized ecological niches has reduced competition between these species. Each species has evolved a beak specialized to take advantage of certain types of food resources.

27. 5-3 What Limits the Growth of Populations? • Concept 5-3 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources.

28. Populations Have Certain Characteristics (1) • Populations differ in • Distribution • Numbers • Age structure • Population dynamics – study of how these characteristics of populations change in response to changes in environmental conditions

29. Populations Have Certain Characteristics (2) • Changes in population characteristics due to: • Temperature • Presence of disease organisms or harmful chemicals • Resource availability • Arrival or disappearance of competing species

30. Most Populations Live Together in Clumps or Patches (1) • Population distribution • Clumping – most populations live in clumps or patches • Ex. Desert veg around a spring; wolf packs • Uniform dispersion • Random dispersion

31. Most Populations Live Together in Clumps or Patches (2) • Why clumping? • Species tend to cluster where resources are available • Groups have a better chance of finding clumped resources • Protects some animals from predators • Packs allow some to get prey • Temporary groups for mating and caring for young Battle at Kruger (shorter version) - YouTube

32. Populations Can Grow, Shrink, or Remain Stable (1) • Population size governed by • Births • Deaths • Immigration • Emigration • Population change = (births + immigration) – (deaths + emigration)

33. Populations Can Grow, Shrink, or Remain Stable (2) • Age structure – can have strong effect on how rapidly a population changes • Pre-reproductive age • Reproductive age • Post-reproductive age Populations w/ even distributions among 3 groups tend to be stable

34. No Population Can Grow Indefinitely: J-Curves and S-Curves (1) • Biotic potential – capacity for pop growth under ideal conditions • Low – large individuals (elephants, whales) • High – small individuals (bacteria, insects) • Intrinsic rate of increase (r) – rate at which pop will grow if had unlimited resources • Individuals in populations with high r • Reproduce early in life • Have short generation times • Can reproduce many times • Have many offspring each time they reproduce

35. No Population Can Grow Indefinitely: J-Curves and S-Curves (2) • Size of populations limited by • Light • Water • Space • Nutrients • Exposure to too many competitors, predators or infectious diseases

36. No Population Can Grow Indefinitely: J-Curves and S-Curves (3) • Environmental resistance - combination of all factors that act to limit growth of population • Carrying capacity (K) – max pop of given species that particular habitat can sustain indefinitely w/o being degraded • Determined by biotic potential & env resistance • Exponential growth – a pop w/ few limitations on resource supplies grows exponentially “J” growth curve • Logistic growth – rapid exponential pop growth followed by steady decrease in growth until pop size levels off • Encounters env resistance • Pop typically fluctuates above & below K • S shaped curve

37. No Population Can Continue to Increase in Size Indefinitely No population can continue to increase in size indefinitely. Exponential growth (left half of the curve) occurs when resources are not limiting and a population can grow at its intrinsic rate of increase (r) or biotic potential. Such exponential growth is converted to logistic growth, in which the growth rate decreases as the population becomes larger and faces environmental resistance. Over time, the population size stabilizes at or near the carrying capacity (K) of its environment, which results in a sigmoid (S-shaped) population growth curve. Depending on resource availability, the size of a population often fluctuates around its carrying capacity, although a population may temporarily exceed its carrying capacity and then suffer a sharp decline or crash in its numbers. See an animation based on this figure at CengageNOW. Question: What is an example of environmental resistance that humans have not been able to overcome?

38. Science Focus: Why Are Protected Sea Otters Making a Slow Comeback? • Low biotic potential • Prey for orcas • Cat parasites • Thorny-headed worms • Toxic algae blooms • PCBs and other toxins • Oil spills To keep from drifting apart, sea otters may sleep holding hands - Author: joemess from austin

39. Population Size of Southern Sea Otters Off the Coast of So. California (U.S.)

40. Logistic Growth of a Sheep Population on the island of Tasmania, 1800–1925 Logistic growth of a sheep population on the island of Tasmania between 1800 and 1925. After sheep were introduced in 1800, their population grew exponentially, thanks to an ample food supply. By 1855, they had overshot the land’s carrying capacity. Their numbers then stabilized and fluctuated around a carrying capacity of about 1.6 million sheep.

41. Active Figure: Exponential growth

42. Animation: Logistic growth

43. When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash • Carrying capacity: not fixed • Can increase or decrease seasonally • Weather conditions (drought) • Abundance of predators or competitors • Reproductive time lag (period needed for birth rate to fall & death rate to rise) may lead to overshoot K • Dieback (crash) • Damage may reduce area’s carrying capacity • Overgrazing cattle – reduced grass cover – increased sagebrush & replace grass – decrease K for cattle

44. Exponential Growth, Overshoot, and Population Crash of a Reindeer Exponential growth, overshoot, and population crash of reindeer introduced to the small Bering Sea island of St. Paul. When 26 reindeer (24 of them female) were introduced in 1910, lichens, mosses, and other food sources were plentiful. By 1935, the herd size had soared to 2,000, overshooting the island’s carrying capacity. This led to a population crash, when the herd size plummeted to only 8 reindeer by 1950. Question: Why do you think this population grew fast and crashed, unlike the sheep in Figure 5-12?

45. Species Have Different Reproductive Patterns • r-Selected species, opportunists – high rate of reproduction • Insects, bacteria, annuals, rodents, frogs • Easily gain foothold in disturbed areas • Often experience boom & bust cycles as competitors move in • K-selected species, competitors • Reproduce later in life w/ fewer offspring • Strong offspring can compete for resources • Do well in competitive conditions when pop near carrying capacity (K) • Humans, whales, sharks, long lived plants, birds of prey

46. Positions of r- and K-Selected Species on the S-Shaped Population Growth Curve Positions of r-selected and K-selected species on the sigmoid (S-shaped) population growth curve.

47. Genetic Diversity Can Affect the Size of Small Populations • Founder effect – a few indiv. Colonize new habitat that’s geogr. Isolated from other members • Limited gen diversity may threaten colony’s survival • Demographic bottleneck – only a few indiv survive catastrophe • Lack of gen diversity may limit ability to rebuild population • Genetic drift – random genetic changes lead to unequal reproductive success • Some indiv breed more & their genes dominate • Inbreeding – can occur from bottleneck; freq of defective genes increase limiting survival • Minimum viable population size – minimum # of indiv certain populations (rare/ endangered) need for long-term survival

48. Under Some Circumstances Population Density Affects Population Size • Population Density - # of indiv in a population found in a particular area or volume • Density-dependent population controls • Predation • Parasitism • Infectious disease • Competition for resources These factors tend to regulate a pop at a constant size often near carrying capacity Density Independent controls- severe freeze, floods, hurricanes, fire, pollution, habitat destruction

49. Several Different Types of Population Change Occur in Nature • Stable – pop size flux slightly above & below K • Found in undisturbed tropical rain forests • Irruptive – pop explodes then crashes • Insects explode in summer & crash in winter • Cyclic fluctuations, boom-and-bust cycles – pop cycles every few years • Top-down population regulation – through predation • Bottom-up population regulation – pred/prey pops controlled by scarcity of resources • Irregular - no pattern to pop size • May be due to flux in response to periodic catastrophic pop crashes

50. Population Cycles for the Snowshoe Hare and Canada Lynx Canadian Lynx V's A Hare - YouTube