Biodiversity, Species Interactions, and Population Control

Biodiversity, Species Interactions, and Population ControlChapter 5 (Miller and Spoolman, 2010)Figure 5.1An 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 their weight in shellfish: clams, mussels, crabs, sea urchins, abalone and 40 other benthic animals.Hunted to near extinction by early 1900sPartial recovery from 1938 to 2007, pop. increased from 50 to about 3000.Helped in part by ESA listing in 1977Why care about sea otters?EthicsKeystone speciesTourism dollars

5-1 How Do Species Interact?Concept 5-1 Five types of species interactionscompetition, predation, parasitism, mutualism, and commensalismaffect the resource use and population sizes of the species in an ecosystem. Species Interact in Five Major WaysInterspecific CompetitionPredationParasitismMutualismCommensalism

These interactions have significant effects on the resources use and pop. sizes of species in an ecosystemAlso 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 ResourcesCompetition is the most common interactionThe greater the niche overlap, the greater the competition.Competitive exclusion principle no two species can occupy the exact same niche.Competition would be too intenseHumans 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 airAmbush predators use stealth and camouflage.Chemical warfareVenomMost Consumer Species Feed on Live Organisms of Other Species (2)Prey escape/avoidance methods:Highly developed senses, sight and smell (so do predators!)Flight responseRun, swim, and fly fastProtective armorShells, bark, spines, thornsCamouflage to hideChemical warfarePoisons (oleander plants, toads), irritants (poison ivy, bombardier beetle), foul odor (skunk, stink bug), bad taste (monarch butterfly)Warning colorationMimicry (viceroy butterfly, milk snake)Deceptive looksDeceptive behaviorSchooling or herding behaviors

Most Consumer Species Feed on Live Organisms of Other Species (3)At the individual levelPredator benefitsPrey species is harmedAt the population levelPredation plays a role in natural selectionPredators 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 5.2Some ways in which prey species avoid their predators: (a, b) camouflage, (ce) 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 forestsRestricted 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 forestsSea urchinsPollution from water run-offGlobal warming

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

Predator and Prey Species Can Drive Each Others EvolutionTo 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 5.3Coevolution. 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 pathogenicTapeworms, liver fluke, TrypanosomaEctoparasitesMosquitoes, fleas, ticks, mistletoe, and sea lampreyOther forms of parasitism: Brood parasitism and klepto-parasitism

Some Species Feed off Other Species by Living on or in Them (2)At the individual levelFor host, parasites are harmful.Parasites benefit.But at the population levelParasites can promote biodiversity by increasing species richness.Help keep a hosts population size in check.

Parasite-host relationship may lead to coevolution

Figure 5.4Parasitism: (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 BenefitMutualism occurs when two species behave in ways that benefit both by providing each with food, shelter, or some other resource.Flower s and their pollinatorsNutrition and protectionGut inhabitant mutualismFigure 5.5Examples 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 HarmedCommensalism is an interaction that benefits one species but has little, if any, effect on the other.

Epiphytes

Birds nesting in trees

Figure 5.6In an example of commensalism, this bromeliadan epiphyte, or air plant, in Brazils Atlantic tropical rain forestroots 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 ResourcesResource partitioning occurs when species competing for similar scarce resources evolve specialized traits that allow them to use shared resourcesat different timesin different waysin different places

Niche overlap can be reduced when natural selection reduces broad and overlapping niches.Species become more specialized.Figure 5.7Competing 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 5.8Sharing 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): 533536.)

Figure 4.13Specialized feeding niches of various bird species in a coastal wetland. This specialization reduces competition and allows sharing of limited resources.

Figure 5.9Specialist 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 inDistributionNumbersAge structureDensity

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:TemperaturePresence of disease organisms or harmful chemicalsResource availabilityArrival or disappearance of competing speciesMost Populations Live Together in Clumps or PatchesThree 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 byBirthsDeathsImmigrationEmigration

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 structurethe 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 individualsHigh, 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 rReproduce early in lifeHave short generation timesCan reproduce many timesHave 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.WaterSpaceNutrientsExposure 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, JLogistic growth rapid growth followed by a steady decrease as a population encounters environmental resistance.Curve shape, S (or sigmoid)Figure 5.11No 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 5.12Logistic 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 lands 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 potentialPrey for orcasCat parasitesThorny-headed wormsToxic algae bloomsPCBs and other toxinsOil spills

Figure 5.BPopulation size of southern sea otters off the coast of the U.S. state of California, 19832007. 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 Habitats Carrying Capacity, Its Population Can CrashCarrying 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 areas carrying capacity.

Figure 5.13Exponential 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 islands 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 5.14Positions 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 PopulationsWhen 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.newscientist.com/article/dn13490 Founder Effect

Under Some Circumstances Population Density Affects Population SizePopulation density the number of individuals in a population found in a particular area or volume.Density-dependent population controlsPredationParasitismInfectious diseaseCompetition for resourcesDensity dependent factors tend to regulate a population at a fairly constant size, often near carrying capacity of an area.Density independent factors are often abioticSevere freeze, hurricanes, fires, pollution, habitat destruction, wetland loss.Several Different Types of Population Change Occur in NatureStableHovers around K.Characteristic of species that live in undisturbed tropical rain forests.IrruptiveIncrease to a high peak and then crashAlgae and insects display this type of population changesLinked to seasonal changes in weather and nutrient availabilityCyclic fluctuations, boom-and-bust cyclesChanges occur in regular cyclesExamples: Lemming populations rise and fall every 3-4 yearsLynx and snowshoe hare every 10 yearsTop-down population regulationBottom-up population regulation Irregular Changes in pop. size with no recurring pattern.Figure 5.15Population 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 controlthrough predation by lynx and other predatorsand 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. MacLulich)

Humans Are Not Exempt from Natures Population ControlsIrelandPotato crop in 1845

Bubonic plagueFourteenth century

AIDSGlobal epidemic

So far, technological, social, and other cultural changes have extended the earths carrying capacity for humans.Case Study: Exploding White-Tailed Deer Population in the U.S.1900: deer habitat destruction and uncontrolled hunting

1920s1930s: laws to protect the deerPop no 25-30 million

Current population explosion for deerIn some forests, they are consuming native ground cover making way for non-native invaders.Lyme diseaseDeer-vehicle accidentsEating garden plants and shrubs

Ways to control the deer population5-4 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 SuccessionTypes 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 successionPrimary successionSecondary successionSome Ecosystems Start from Scratch: Primary SuccessionPrimary succession begins with a lifeless area where there isNo soil in a terrestrial systemNo bottom sediment in an aquatic systemEarly successional plant species, called pioneer, or colonizing species.Lichens and mossesMidsuccessional plant speciesHerbs, grasses and shrubs, and later treesLate successional plant speciesOther treesCan also occur in ponds.Figure 5.16Primary 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 DisturbedRemovedDestroyed

Some soil remains in a terrestrial system

Some bottom sediment remains in an aquatic systemFigure 5.17Natural 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 150200 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 successionTend to increase biodiversityIncrease species richness and interactions among speciesAre accompanied by succession of faunal species

Primary and secondary succession can be interrupted byFiresHurricanesClear-cutting of forestsPlowing of grasslandsInvasion 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 Doesnt Follow a Predictable PathTraditional view Balance of nature and a climax community

Current view Ever-changing mosaic of patches of vegetationMature late-successional ecosystems State of continual disturbance and change

Living Systems Are Sustained through Constant ChangeInertia, or persistenceAbility 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