Biodiversity Species Interactions and Population Control Chapter 5

Biodiversity, Species Interactions, and Population Control Chapter 5 (Miller and Spoolman, 2010)

Figure 5. 1 An endangered southern sea otter in Monterey Bay, California (USA), uses a stone to crack the shell of a clam (insert). It lives in a giant kelp bed near San Clemente Island, California (background). Scientific studies indicate that the otters act as a keystone species in a kelp forest system by helping to control the populations of sea urchins and other kelp-eating species.

Core Case Study: Southern Sea Otters: Are They Back from the Brink of Extinction? �Habitat: giant kelp forest of Pacific Coast of N. A. �Fast agile swimmers that eat about ¼ their weight in shellfish: clams, mussels, crabs, sea urchins, abalone and 40 other benthic animals. �Hunted to near extinction by early 1900 s �Partial recovery from 1938 to 2007, pop. increased from 50 to about 3000. �Helped in part by ESA listing in 1977 �Why care about sea otters? �Ethics �Keystone species �Tourism dollars

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.

Species Interact in Five Major Ways �Interspecific Competition �Predation �Parasitism �Mutualism �Commensalism �These interactions have significant effects on the resources use and pop. sizes of species in an ecosystem �Also influence the abilities of the interacting species to survive, thus the interactions are agents of natural selection.

Most Species Compete with One Another for Certain Resources �Competition is the most common interaction �The greater the niche overlap, the greater the competition. �Competitive exclusion principle – no two species can occupy the exact same niche. �Competition would be too intense �Humans are outcompeting other species for space food and other resources as our ecological footprint increases.

Most Consumer Species Feed on Live Organisms of Other Species (1) �Predation is when a member of species feeds directly on all or part of a living organism of another plant or animal. �Predator and prey form a predator-prey relationship. �Herbivores, carnivores, and omnivores are predators. �Methods of Prey Capture by Predators: �Herbivores � walk, swim, or fly up to plants they feed on. �Carnivores � Pursuit requires speed and agility on ground, in water, or in the air � Ambush predators use stealth and camouflage. �Chemical warfare � Venom

Most Consumer Species Feed on Live Organisms of Other Species (2) �Prey escape/avoidance methods: �Highly developed senses, sight and smell (so do predators!) �Flight response � Run, swim, and fly fast �Protective armor � Shells, bark, spines, thorns �Camouflage to hide �Chemical warfare � Poisons (oleander plants, toads), irritants (poison ivy, bombardier beetle), foul odor (skunk, stink bug), bad taste (monarch butterfly) �Warning coloration �Mimicry (viceroy butterfly, milk snake) �Deceptive looks �Deceptive behavior �Schooling or herding behaviors

Most Consumer Species Feed on Live Organisms of Other Species (3) �At the individual level �Predator benefits �Prey species is harmed �At the population level �Predation plays a role in natural selection � Predators take the sick, weak, old, and less fit members of the prey species. �Some people view predators with contempt. If you were an ambassador for nature, what would you tell these people?

Figure 5. 2 Some ways in which prey species avoid their predators: (a, b) camouflage, (c–e) chemical warfare, (d, e) warning coloration, (f) mimicry, (g) deceptive looks, and (h) deceptive behavior.

Science Focus: Why Should We Care about Kelp Forests? �Kelp forests �Restricted to cold, nutrient-rich, and fairly shallow coastal waters. �One of most biologically diverse marine ecosystems supporting large numbers of marine plants and animals. �Help reduce shore erosion. �Harvested as a renewable resource for algin found in blades. � Used in toothpaste, ice cream, and many other products. �Major threats to kelp forests �Sea urchins �Pollution from water run-off �Global warming

Figure 5 -A Purple sea urchin in coastal waters of the U. S. state of CA.

Predator and Prey Species Can Drive Each Other’s Evolution �To survive, predators must eat and prey must avoid being eaten Predators and prey populations exert intense natural selection pressures on one another. �Coevolution occurs when populations of two different species interact over such a long period of time, changes in the gene pool of one species can lead to changes in the gene pool of the other species.

Figure 5. 3 Coevolution. A Langohrfledermaus bat hunting a moth. Long-term interactions between bats and their prey such as moths and butterflies can lead to coevolution, as the bats evolve traits that increase their chances of getting a meal and the moths evolve traits that help them avoid being eaten.

Some Species Feed off Other Species by Living on or in Them (1) �Parasitism occurs when one species (the parasite) feeds on the body of, or the energy used by, another organism, usually by living on or in the host. �Parasites rarely kill host, but may gradually weaken them. �Endoparasites, some pathogenic � Tapeworms, liver fluke, Trypanosoma �Ectoparasites � Mosquitoes, fleas, ticks, mistletoe, and sea lamprey �Other forms of parasitism: Brood parasitism and klepto- parasitism

Some Species Feed off Other Species by Living on or in Them (2) �At the individual level �For host, parasites are harmful. �Parasites benefit. �But at the population level �Parasites can promote biodiversity by increasing species richness. �Help keep a host’s population size in check. �Parasite-host relationship may lead to coevolution

Figure 5. 4 Parasitism: (a) Healthy tree on the left and an unhealthy one on the right, which is infested with parasitic mistletoe. (b) Blood-sucking parasitic sea lampreys attached to an adult lake trout from the Great Lakes (USA).

In Some Interactions, Both Species Benefit �Mutualism occurs when two species behave in ways that benefit both by providing each with food, shelter, or some other resource. �Flower s and their pollinators �Nutrition and protection �Gut inhabitant mutualism

Figure 5. 5 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.

In Some Interactions, One Species Benefits and the Other Is Not Harmed �Commensalism is an interaction that benefits one species but has little, if any, effect on the other. �Epiphytes �Birds nesting in trees

Figure 5. 6 In an example of commensalism, this bromeliad—an epiphyte, or air plant, in Brazil’s Atlantic tropical rain forest—roots on the trunk of a tree, rather than in soil, without penetrating or harming the tree. In this interaction, the epiphyte gains access to water, other nutrient debris, and sunlight; the tree apparently remains unharmed.

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.

Some Species Evolve Ways to Share Resources �Resource partitioning occurs when species competing for similar scarce resources evolve specialized traits that allow them to use shared resources �at different times �in different ways �in different places �Niche overlap can be reduced when natural selection reduces broad and overlapping niches. �Species become more specialized.

Figure 5. 7 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.

Figure 5. 8 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. Mac. Arthur, “Population Ecology of Some Warblers in Northeastern Coniferous Forests, ” Ecology 36 (1958): 533– 536. )

Figure 4. 13 Specialized feeding niches of various bird species in a coastal wetland. This specialization reduces competition and allows sharing of limited resources.

Figure 5. 9 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.

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.

Populations Have Certain Characteristics (1) �Populations differ in �Distribution �Numbers �Age structure �Density �Population dynamics is the study of how characteristics of populations change in response to changes in environmental conditions.

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

Most Populations Live Together in Clumps or Patches �Three general patterns of population distribution or dispersion in a habitat. �Clumping, most common as resources are also clumped. �Uniform dispersion, when resources is even and scarce. �Random dispersion, not as common. �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.

Figure 5. 10 Generalized dispersion patterns. The most common pattern is clumps of members of a population scattered throughout their habitat, mostly because resources are usually found in patches. Questions: Why do you think the creosote bushes are uniformly spaced while the dandelions are not?

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

Populations Can Grow, Shrink, or Remain Stable (2) �How fast a population grows or declines depends on its age structure—the proportions of individuals at various ages. � Prereproductive age: not mature enough to reproduce. �Reproductive age: those capable of reproduction. �Postreproductive age: those too old to reproduce.

No Population Can Grow Indefinitely: J-Curves and S-Curves (1) �Biotic potential is the capacity for population growth under ideal conditions. � Low, usu. in species with large individuals � High, usu. in small species. �Intrinsic rate of increase (r) is the rate at which the population of a species grows if it 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

No Population Can Grow Indefinitely: J-Curves and S-Curves (2) �Size of populations is regulated by limiting factors. �Water �Space �Nutrients �Exposure to too many competitors, predators or infectious diseases

No Population Can Grow Indefinitely: J-Curves and S-Curves (3) �Environmental resistance is the combination of all factors that act to limit the growth of a population. �Biotic potential and environmental resistance determine carrying capacity (K)—the maximum population of a given species that a particular habitat can sustain indefinitely without being degraded. �Exponential growth – growth at a fixed rate relative to the population size, e. g. 2 % annually. �Curve shape, J �Logistic growth – rapid growth followed by a steady decrease as a population encounters environmental resistance. �Curve shape, S (or sigmoid)

Figure 5. 11 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. Question: What is an example of environmental resistance that humans have not been able to overcome?

Figure 5. 12 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.

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 Figure 5. B Population size of southern sea otters off the coast of the U. S. state of California, 1983– 2007. According to the U. S. Fish and Wildlife Service, the sea otter population would have to reach about 8, 400 animals before it can be removed from the endangered species list. (Data from U. S. Geological Survey)

When a Population Exceeds Its Habitat’s Carrying Capacity, Its Population Can Crash �Carrying capacity is not fixed. �Reproductive time lag may lead to overshoot of K. �The time lag is the period needed for the birth rate to decrease and the death rate to increase in response to resource overconsumption. � Dieback, or crash �Damage from overconsumption/use may reduce area’s carrying capacity.

Figure 5. 13 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?

Species Have Different Reproductive Patterns Natural capital: generalized characteristics of r-selected (opportunist) species and K-selected (competitor) species. Many species have characteristics between these two extremes.

Figure 5. 14 Positions of r-selected and K-selected species on the sigmoid (S-shaped) population growth curve.

When does death come? Survivorship curves for populations of different species, show the percentages of the members of a population surviving at different ages. Most members of a late loss population (such as elephants, rhinoceroses, and humans) live to an old age. Members of a constant loss population (such as many songbirds) die at all ages. In an early loss population (such as annual plants and many bony fish species), most members die at a young age. These generalized survivorship curves only approximate the realities of nature.

Genetic Diversity Can Affect the Size of Small Populations �When a population becomes so reduced, reduced genetic diversity can affect the overall survival of the population. �Genetic drift – random changes in gene (i. e. , allele) frequencies in a population that can lead to unequal reproductive success; occurs more often in small populations. � Founder effect – when a few members of a population colonize a new area and become geographically isolated. � Demographic bottleneck – occurs when only a few member of a population survive a catastrophic die-off. � Inbreeding – occurs when individuals of small population mate with each other increase in the freq. of defective genes. �Minimum viable population size – the number of individuals a population needs for long-term survival.

Random Effects on Allele Frequency in Small Populations

Genetic Bottleneck http: //www. newsc ientist. com/article /dn 13490

Founder Effect

Under Some Circumstances Population Density Affects Population Size �Population density – the number of individuals in a population found in a particular area or volume. �Density-dependent population controls �Predation �Parasitism �Infectious disease �Competition for resources �Density dependent factors tend to regulate a population at a fairly constant size, often near carrying capacity of an area. �Density independent factors are often abiotic �Severe freeze, hurricanes, fires, pollution, habitat destruction, wetland loss.

Several Different Types of Population Change Occur in Nature � Stable � Hovers around K. � Characteristic of species that live in undisturbed tropical rain forests. � Irruptive � Increase to a high peak and then crash � Algae and insects display this type of population changes � Linked to seasonal changes in weather and nutrient availability � Cyclic fluctuations, boom-and-bust cycles � Changes occur in regular cycles � Examples: � � Lemming populations rise and fall every 3 -4 years Lynx and snowshoe hare every 10 years � Top-down population regulation � Bottom-up population regulation � Irregular � Changes in pop. size with no recurring pattern.

Figure 5. 15 Population cycles for the snowshoe hare and Canada lynx. At one time, scientists believed these curves provided circumstantial evidence that these predator and prey populations regulated one another. More recent research suggests that the periodic swings in the hare population are caused by a combination of top-down population control—through predation by lynx and other predators—and bottom-up population control, in which changes in the availability of the food supply for hares help determine hare population size, which in turn helps determine the lynx population size. (Data from D. A. Mac. Lulich)

Humans Are Not Exempt from Nature’s Population Controls �Ireland �Potato crop in 1845 �Bubonic plague �Fourteenth century �AIDS �Global epidemic �So far, technological, social, and other cultural changes have extended the earth’s carrying capacity for humans.

Case Study: Exploding White-Tailed Deer Population in the U. S. � 1900: deer habitat destruction and uncontrolled hunting � 1920 s– 1930 s: laws to protect the deer �Pop no 25 -30 million �Current population explosion for deer �In some forests, they are consuming native ground cover making way for non-native invaders. �Lyme disease �Deer-vehicle accidents �Eating garden plants and shrubs �Ways to control the deer population

5 -4 How Do Communities and Ecosystems Respond to Changing Environmental Conditions? �Concept 5 -4 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 �Types and numbers of species change in a biological community over time. �Mature forests and other ecosystems do not spring up from bare rock. �Instead they go through changes in species composition over long periods of time. �Ecological succession �Primary succession �Secondary succession

Some Ecosystems Start from Scratch: Primary Succession �Primary succession begins with a lifeless area where there is �No soil in a terrestrial system �No bottom sediment in an aquatic system �Early successional plant species, called pioneer, or colonizing species. �Lichens and mosses Ca na i n p lso �Midsuccessional plant species on oc d �Herbs, grasses and shrubs, and later trees s. cur �Late successional plant species �Other trees

Figure 5. 16 Primary ecological succession. Over almost a thousand years, plant communities developed, starting on bare rock exposed by a retreating glacier on Isle Royal, Michigan (USA) in northern Lake Superior. The details of this process vary from one site to another. Question: What are two ways in which lichens, mosses, and plants might get started growing on bare rock?

Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession (1) �Secondary succession begins in an area �Disturbed �Removed �Destroyed �Some soil remains in a terrestrial system �Some bottom sediment remains in an aquatic system

Figure 5. 17 Natural ecological restoration of disturbed land. 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. A new disturbance, such as deforestation or fire, would create conditions favoring pioneer species such as annual weeds. In the absence of new disturbances, secondary succession would recur over time, but not necessarily in the same sequence shown here. Questions: Do you think the annual weeds (left) would continue to thrive in the mature forest (right)? Why or why not?

Some Ecosystems Do Not Have to Start from Scratch: Secondary Succession (2) �Primary and secondary succession �Tend to increase biodiversity �Increase species richness and interactions among species �Are accompanied by succession of faunal species �Primary and secondary succession can be interrupted by �Fires �Hurricanes �Clear-cutting of forests �Plowing of grasslands �Invasion by nonnative species

Science Focus: How Do Species Replace One Another in Ecological Succession? �Facilitation is when one set of species makes an area suitable for species with different niche requirements. �Inhibition is when some early species hinder the establishment and growth of other species. �Some plants produce allopathic compounds. �Tolerance may be observed when late successional plants are largely unaffected by plants at earlier stages because they are not in direct competition with them for key resources. �For example, shade tolerant trees.

Succession Doesn’t Follow a Predictable Path �Traditional view � Balance of nature and a climax community �Current view �Ever-changing mosaic of patches of vegetation �Mature late-successional ecosystems � State of continual disturbance and change

Living Systems Are Sustained through Constant Change �Inertia, or persistence �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 �Tipping point