Biodiversity, Species Interactions, and Population Control 5 Biodiversity, Species Interactions, and Population Control

Core Case Study: Southern Sea Otters - A Species in Recovery Live in giant kelp forests By the early 1900s they had been hunted almost to extinction Partial recovery since 1977 Why care about sea otters? Ethics Tourism dollars Keystone species

Southern Sea Otter Figure 5.1 An endangered southern sea otter in Monterey Bay, California (USA) uses a stone to crack the shells of clams that it feeds on (left). It lives in a giant bed of seaweed called kelp (right). Fig. 5-1, p. 102

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

Most Species Compete with One Another for Certain Resources Five basic types of interactions Interspecific Competition Predation Parasitism Mutualism Commensalism Interspecific competition Compete to use the same limited resources

Some Species Evolve Ways to Share Resources Resource partitioning Species may use only parts of resource At different times In different ways

Sharing the Wealth Blackburnian Warbler Black-throated Green Warbler Cape May Warbler Bay-breasted Warbler Yellow-rumped Warbler Figure 5.2 Sharing the wealth: Resource partitioning among five species of insect-eating warblers in the spruce forests of the U.S. state of Maine. Each species spends at least half its feeding time in its associated yellow-highlighted areas of these spruce trees. Stepped Art Fig. 5-2, p. 103

Insect and nectar eaters Specialist Species of Honeycreepers Fruit and seed eaters Insect and nectar eaters Greater Koa-finch Kuai Akialaoa Amakihi Kona Grosbeak Crested Honeycreeper Akiapolaau Figure 5.3 Specialist species of honeycreepers: Through natural selection, different species of honeycreepers have shared resources by evolving specialized beaks to take advantage of certain types of food such as insects, seeds, fruits, and nectar from certain flowers. Question: Look at each bird’s beak and take a guess at what sort of food that bird might eat. Maui Parrotbill Apapane Unkown finch ancestor Fig. 5-3, p. 104

Consumer Species Feed on Other Species Predator – feeds directly on all or part of a living organism Carnivores Pursuit and ambush Camouflage Chemical warfare

Consumer Species Feed on Other Species (cont’d.) Prey can avoid predation Camouflage Chemical warfare Warning coloration Mimicry Behavioral strategies

Predator-Prey Relationships Figure 5-4: Predator-prey relationship: This brown bear (the predator) in the U.S. state of Alaska has captured and will feed on this salmon (the prey). Fig. 5-4, p. 104

Predator-Prey Relationships Figure 5-6 These prey species have developed specialized ways to avoid their predators: (a, b) camouflage, (c, d, e) chemical warfare, (d, e, f) warning coloration, (f) mimicry, (g) deceptive looks, and (h) deceptive behavior. Fig. 5-6, p. 106

Interactions between Predator and Prey Species Intense natural selection pressures between predator and prey populations Coevolution Interact over a long period of time Changes in the gene pool of one species can cause changes in the gene pool of the other Bats and moths Echolocation of bats and sensitive hearing of moths

Coevolution Figure 5-7: Coevolution: This bat is using ultrasound to hunt a moth. As the bats evolve traits to increase their chance of getting a meal, the moths evolve traits to help them avoid being eaten. Fig. 5-7, p. 107

Some Species Feed off Other Species by Living on or inside Them Parasitism Parasite is usually much smaller than the host Parasite rarely kills the host Parasite-host interaction may lead to coevolution

Parasitism Figure 5-8: Parasitism: This blood-sucking, parasitic sea lamprey has attached itself to an adult lake trout from the Great Lakes (USA, Canada). Fig. 5-8, p. 107

In Some Interactions, Both Species Benefit Mutualism Nutrition and protective relationship Gut inhabitant mutualism Not cooperation – mutual exploitation

Mutualism Figure 5-9: Mutualism: Oxpeckers feed on parasitic ticks that infest animals such as this impala and warn of approaching predators. Fig. 5-9, p. 108

In Some Interactions, One Species Benefits and the Other Is Not Harmed Commensalism Benefits one species and has little affect on the other Epiphytes Birds nesting in trees

Commensalism Figure 5-10: In an example of commensalism, this pitcher plant is attached to a branch of a tree without penetrating or harming the tree. This carnivorous plant feeds on insects that become trapped inside it. Fig. 5-10, p. 108

5-2 Responding to Changing Environmental Conditions How do communities and ecosystems respond to changing environmental conditions? The structure and species composition of communities and ecosystems change in response to changing environmental conditions through a process called ecological succession

Communities and Ecosystems Change over Time: Ecological Succession Gradual change in species composition Primary succession In lifeless areas Secondary succession Areas of environmental disturbance Examples of natural ecological restoration

Primary Ecological Succession Figure 5.11 Primary ecological succession: Over almost a 1,000 years, these plant communities developed, starting on bare rock exposed by a retreating glacier on Isle Royal, Michigan (USA) in western Lake Superior. The details of this process vary from one site to another. 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 Fig. 5-11, p. 109

Natural Ecological Restoration Animated Figure 5.12 Natural ecological restoration of disturbed land: This diagram shows the undisturbed secondary ecological succession of plant communities on an abandoned farm field in the U.S. state of North Carolina. It took 150–200 years after the farmland was abandoned for the area to become covered with a mature oak and hickory forest. 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 Fig. 5-12, p. 110

Ecological Succession Does Not Follow a Predictable Path Traditional view Balance of nature and climax communities Current view Ever-changing mosaic of patches of vegetation in different stages of succession

Living Systems Are Sustained through Constant Change Inertia Ability of a living system to survive moderate disturbances Resilience Ability of a living system to be restored through secondary succession after a moderate disturbance

What Limits the Growth of Populations No population can grow indefinitely because of limitations on resources and because of competition among species for those resources

Most Populations Live in Clumps Group of interbreeding individuals of the same species Population distribution Clumping Species cluster for resources Protection from predators Ability to hunt in packs

A School of Anthias Fish Figure 5-13: A population, or school, of Anthias fish on coral in Australia’s Great Barrier Reef. Fig. 5-13, p. 111

Populations Can Grow, Shrink, or Remain Stable Population size governed by: Births and deaths; immigration and emigration Population change = (births + immigration) – (deaths + emigration) Age structure Pre-reproductive age Reproductive age Post-reproductive age

Some Factors Can Limit Population Size Range of tolerance Variations in physical and chemical environment Individuals may have different tolerance ranges

Some Factors Can Limit Population Size Limiting factor principle Too much or too little of any physical or chemical factor can limit or prevent growth of a population, even if all other factors are at or near the optimal range of tolerance Precipitation, nutrients, sunlight Populations density Number of individuals in a given area

Zone of physiological stress Zone of physiological stress Trout Tolerance of Temperature Lower limit of tolerance Higher limit of tolerance No organisms Few organisms Few organisms No organisms Abundance of organisms Population size Figure 5.15 Range of tolerance for a population of trout to changes in water temperature. Zone of intolerance Zone of physiological stress Zone of physiological stress Zone of intolerance Optimum range Low Temperature High Fig. 5-13, p. 113

Different Species Have Different Reproductive Patterns Some species: Have many small offspring Little parental involvement Other species: Reproduce later in life Have small number of offspring

No Population Can Grow Indefinitely: J-Curves and S-Curves There are always limits to population growth in nature Environmental resistance – factors that limit population growth Carrying capacity Maximum population of a given species that a particular habitat can sustain indefinitely

No Population Can Grow Indefinitely: J-Curves and S-Curves (cont’d.) Exponential growth At a fixed percentage per year Logistic growth Population faces environmental resistance

Growth of a Sheep Population Population overshoots carrying capacity Environmental resistance 2.0 Carrying capacity 1.5 Population recovers and stabilizes Number of sheep (millions) Population runs out of resources and crashes 1.0 Exponential growth Animated Figure 5.16 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 and few predators. 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. .5 1800 1825 1850 1875 1900 1925 Year Fig. 5-16, p. 115

Case Study: Exploding White-Tailed Deer Population in the U.S. 1900 – deer habitat destruction and uncontrolled hunting 1920s–1930s – laws to protect the deer Current deer population explosion Spread Lyme disease Deer-vehicle accidents Eating garden plants and shrubs How can we control the deer population?

White-Tailed Deer Populations Figure 5-17: White-tailed deer populations in the United States have been growing. Fig. 5-17, p. 115

When a Population Exceeds Its Carrying Capacity It Can Crash A population exceeds the area’s carrying capacity Reproductive time lag may lead to overshoot Subsequent population crash Damage may reduce area’s carrying capacity

Population Crash Population overshoots carrying capacity 2,000 1,500 Population crashes Number of reindeer 1,000 Figure 5.18 Exponential growth, overshoot, and population crash of reindeer introduced onto the small Bering Sea island of St. Paul in 1910. 500 Carrying capacity 1910 1920 1930 1940 1950 Year Fig. 5-18, p. 116

Humans Are Not Exempt from Nature’s Population Controls Ireland Potato crop in 1845 Bubonic plague Fourteenth century AIDS Current global epidemic

Three Big Ideas Certain interactions among species Affect their use of resources and their population sizes Changes in environmental conditions Cause communities and ecosystems to gradually alter their species composition and population sizes (ecological succession) There are always limits to population growth in nature

Tying It All Together – Southern Sea Otters and Sustainability Before European settlers in the U.S., the sea otter ecosystem was complex Settlers began hunting otters Disturbed the balance of the ecosystem Populations depend on solar energy and nutrient cycling When these are disrupted biodiversity is threatened