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BIODIVERSITY, SPECIES INTERACTIONS, AND POPULATION CONTROL Chapter 5 CORE CASE STUDY: SOUTHERN SEA OTTERS: ARE THEY BACK FROM THE BRINK OF EXTINCTION? Habitat Live in giant kelp forests (California, West Coast) Prey on many kelp-eating shellfish Hunted: early 1900s Fur traders Competition with local shell-fisherman Partial recovery (still endangered, though) FWS declared endangered, numbers grew from 50 to 2,654 Why care about sea otters? Ethics Tourism dollars Keystone species Control population of shellfish that would otherwise exploit the kelp forests SOUTHERN SEA OTTER Fig. 5-1a, p. 104 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- members of different species compete for resources Predation-one species feeds directly on another Symbiotic Interactions Parasitism-one species uses a another as a host to gain nutrients in a way that it harms the host. Usually on or in the host Mutualism- interactions between two different species in which both species benefit from each other Commensalism- interaction between 2 species where one species benefits and the other is neither helped nor harmed (neutral) MOST SPECIES COMPETE WITH ONE ANOTHER FOR CERTAIN RESOURCES Competition: Actual fighting Mostly one species becoming more efficient at gaining resources Remember every species occupies a special ecological niche Some niches overlap When they both require the same resources The greater amount of shared resources, the more intense competition OVERLAPPING NICHES RESULT IN… When one species is much more efficient at obtaining resources, the other must either: Move (if possible) Alter (reduce or shift) its niche through natural selection Suffer population decline Become extinct SOME SPECIES EVOLVE WAYS TO SHARE RESOURCES Resource partitioning Using only parts of resource Using at different times Using in different ways These different species of birds feed on different parts of the spruce tree to partition their resources. Some feed on different insect species Black burnian Warbler Black-throated Green Warbler Cape May Warbler Bay-breasted Warbler Yellow-rumped Warbler Fig. 5-2, p. 106 SPECIALIST SPECIES OF HONEYCREEPERS Honeycreepers of Hawaii descended from one common ancestor, now have differentiated in beak shapes to partition their resources Fig. 5-3, p. 107 MOST CONSUMER SPECIES FEED ON LIVE ORGANISMS OF OTHER SPECIES Predators capture prey several ways Herbivores: Swim, walk, fly up to plants they feed on Carnivores: 2 options: pursuit and ambush Cooperative hunting: pack of lions hunting giraffes Camouflage: Hide in plain sight and ambush Examples: praying mantis, snowy owls Chemical warfare: Poisonous snakes and spiders (examples) PREDATOR-PREY RELATIONSHIPS Fig. 5-4, p. 107 PREY SPECIES HAVE EVOLVED WAYS TO AVOID PREDATORS Exceptional ability to run, swim, fly away Highly developed senses (sight and smell) Protective physical features: Shells Thick bark Spines Thorns Lizard tails Break off when attacked and give extra time to escape PREY SPECIES HAVE EVOLVED WAYS TO AVOID PREDATORS Camouflage Chemical Warfare Poison Irritants Foul-smelling, bad tasting Squids, octopus emit ink clouds to confuse predators Warning coloration Mimicry Non-harmful prey that mimic more risky prey Ex. The Viceroy butterfly looks and acts like monarch which is poisonous Deceptive looks and behavior Moths, blow fish (a) Span worm (c) Bombardier beetle (e) Poison dart frog (g) Hind wings of Io moth resemble eyes of a much larger animal. (b) Wandering leaf insect (d) Foul-tasting monarch butterfly (f) Viceroy butterfly mimics monarch butterfly (h) When touched, snake caterpillar changes shape to look like head of snake. Stepped Art Fig. 5-5, p. 109 SCIENCE FOCUS: THREATS TO KELP FORESTS Kelp forests: biologically diverse marine habitat Extract the substance algin from kelp for use as a renewable resource Used in toothpaste, cosmetics, ice-cream, and more Major threats to kelp forests 1. Sea urchins- feed on kelp 2. Pollution from water run-off 3. Global warming PURPLE SEA URCHIN Fig. 5-A, p. 108 PREDATOR AND PREY INTERACTIONS CAN DRIVE EACH OTHER’S EVOLUTION Intense natural selection pressures between predator and prey populations Both prey and predator evolve adaptations to survive Coevolution Definition: when two species interact with each other over 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. Interact over a long period of time Bats and moths: echolocation of bats and sensitive hearing of moths COEVOLUTION: A LANGOHRFLEDERMAUS BAT HUNTING A MOTH Fig. 5-6, p. 110 SOME SPECIES FEED OFF OTHER SPECIES BY LIVING ON OR IN THEM Parasitism Parasite is usually much smaller than the host Parasite rarely kills the host Mostly draw nourishment from host and gradually weaken them over time Parasites may have a negative reputation, but they never-the-less add to species biodiversity May live inside or outside host Examples: tapeworms, ticks, sea lampreys, fleas, mistletoe plants PARASITISM: TROUT WITH BLOOD-SUCKING SEA LAMPREY Fig. 5-7, p. 110 MUTUALISM Two interacting species benefit each other by doing so Examples: Bees/butterflies/mosquitos/hummingbirds and flowering plants (pollination) Clownfish and sea anenomes Oxpeckers and black rhinoceros Gut inhabitant mutualism: beneficial bacteria in digestive systems Note: mutualism is not a cooperative agreement. Unintentional benefit by exploiting each other Each species is in it for themselves MUTUALISM: OXPECKERS CLEAN RHINOCEROS; ANEMONES PROTECT AND FEED CLOWNFISH Fig. 5-9, p. 111 COMMENSALISM Interaction where one species benefits and the other is neither helped, nor harmed (just neutral) Examples: Epiphytes: “air plants” attach themselves to trunks or branches of large trees Gain better access to sunlight, nutrients; gain a solid base on which to grow Birds nesting in trees Bromeliad Epiphyte 5-2 WHAT LIMITS THE GROWTH OF POPULATIONS? Concept 5-2 No population can continue to grow indefinitely because of limitations on resources and because of competition among species for those resources. MOST POPULATIONS LIVE TOGETHER IN CLUMPS OR PATCHES (1) Population: group of interbreeding individuals of the same species Population distribution 1. 2. 3. Clumping Uniform dispersion Random dispersion MOST POPULATIONS LIVE TOGETHER IN CLUMPS OR PATCHES (2) Why clumping? 1. Species tend to cluster where resources are available 2. Groups have a better chance of finding clumped resources 3. Protects some animals from predators 4. Packs allow some to get prey POPULATIONS CAN GROW, SHRINK, OR REMAIN STABLE (1) Population size governed by Births Deaths Immigration Emigration Population change = (births + immigration) – (deaths + emigration) Negative value means population is shrinking Positive value means population is growing 0 means stable POPULATIONS CAN GROW, SHRINK, OR REMAIN STABLE (2) Age structure: Distribution of individuals among various age groups in a population Can have strong effects on how fast a population grows or shrinks Age groups described as: Pre-reproductive age Reproductive age Post-reproductive age Population most likely to grow fast the more individuals there are in the reproductive age group AGE STRUCTURE GRAPHS Why is taking gender into account important? Would a population grow faster with more men than women or women than men at reproductive ages? What does this depend on? SOME FACTORS CAN LIMIT POPULATION SIZE Range of tolerance Variations in physical and chemical environment Some individuals within a population can be slightly more tolerant (see next slide 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, etc TROUT TOLERANCE OF TEMPERATURE Fig. 5-13, p. 113 LIMITING FACTORS CONTROL POPULATION SIZES Important Land Limiting Factors: Precipitation/water Soil nutrients Temperature Important Aquatic Limiting Factors Temperature Sunlight Nutrient availability Dissolved oxygen levels Salinity NO POPULATION CAN GROW INDEFINITELY: J-CURVES AND S-CURVES (1) Size of populations controlled by limiting factors: Light Water Space Nutrients Exposure to too many competitors, predators or infectious diseases There will always be limits to population growth No population can grow indefinitely NO POPULATION CAN GROW INDEFINITELY: J-CURVES AND S-CURVES (2) Environmental resistance All factors that act to limit the growth of a population Determines a population’s carrying capacity Carrying capacity (K) Maximum population a given habitat can sustain When populations near the (K), growth RATE begins to slow/decline NO POPULATION CAN GROW INDEFINITELY: J-CURVES AND S-CURVES (3) Exponential growth (J-curve) Starts slowly, then accelerates to carrying capacity when meets environmental resistance Logistic growth (S-curve) Decreased population growth rate as population size reaches carrying capacity LOGISTIC GROWTH OF SHEEP IN TASMANIA Note how the population size fluctuates, it never truly stabilizes. Overshoot usually occurs, knocks the population back down, and up again. Fig. 5-15, p. 115 SCIENCE FOCUS: THREAT ON CALIFORNIA’S SOUTHERN SEA OTTER Low reproductive rates Sexual maturity between 2-5 years old 1 pup per yea Threats Predation from Orcas Parasites from cat litter Thorny -headed worms from seagulls Toxic algal blooms Biomagnification from PCB’s Oil Spills They serve as indicator species why? POPULATION SIZE OF SOUTHERN SEA OTTERS OFF THE COAST OF SO. CALIFORNIA (U.S.) Fig. 5-B, p. 114 CASE STUDY: WHITE TAILED DEER POPULATIONS White Tailed Deer were greatly threatened in the early 1900’s Due to habitat destruction and hunting Laws were passed in 1920’s-30’s to protect remaining deer Methods used included Restricted hunting Elimination of predators Protection methods worked too well Population boom CASE STUDY: WHITE TAILED DEER Problems with deer population explosion Deer are exploiting suburban areas (feeding on suburbanite’s gardens and farmer’s land) Spreading Lyme disease to humans (via ticks) Increased vehicular accidents, human fatalities Control methods: Hunting re-opened Spray predator-scented sprays as a scare tactic Trapped and moved Birth control darts POPULATION CRASH AFTER EXCEEDING CARRYING CAPACIT Y Some populations temporarily exceed the ( K) known as OVERSHOOT A drastic crash may occur if there is a reproductive time lag Period needed for the birth rate to fall and for the death rate to rise in response to over consumption This is known as a population Crash, or dieback CARRYING CAPACIT Y IS NOT FIXED Factors may increase or decrease (k) Seasonality Presence/absence of predators Abundance/scarcity of competitors Habitat degradation SPECIES HAVE DIFFERENT REPRODUCTIVE RATES Some species reproduce many, small offspring Do not need to provide significant parental care Why not? Many offspring = greater chances of survival The number of pre-reproductive deaths will most likely always remain less than the total offspring produced Conserves time/energy for parent offspring Some species reproduce later in life and have few offspring Mature slowly Require parental care Which are most susceptible to extinction? Why? SURVIVORSHIP CURVES http://apbiology.chsd218.richards.schoolfusion.us/modules/groups/homepagefiles/gwp/805395/918350/File/Unit_01_Ecolo gy/Survivorship_Curves.swf?sessionid=44c50c7ebdcd89a975e40de7289bbd56 REPRODUCTIVE STRATEGIES (R & K) R - Unstable environment, density independent small size of organism energy used to make each individual is low many offspring are produced early maturity short life expectancy each individual reproduces only once type III survivorship pattern in which most of the individuals die within a short time but a few live much longer K - Stable environment, density dependent interactions large size of organism energy used to make each individual is high few offspring are produced late maturity, often after a prolonged period of parental care long life expectancy individuals can reproduce more than once in their lifetime type I or II survivorship pattern in which most individuals live to near the maximum life span http://www.bio.miami.edu/tom/courses/bil160/bil160goods/16_rKselection.html REPRODUCTIVE PATTERNS r-selected species tend to be opportunists while K-selected species tend to be competitors. Figure 8-10 R-SELECTED VS. K-SELECTED POPULATION DENSIT Y Population Density: number of individuals in a population found in a particular area or volume DENSIT Y-DEPENDENT VS DENSIT Y INDEPENDENT FACTORS Density Dependent factors Have a greater effect as a population increases in density Examples: infectious disease, competition, space, predation, parasitism Musical Chairs! Density-Independent Factors Does not matter how dense a population is Examples: seasonal change, catastrophic event, habitat destruction Think of a population of plants that experience a winter freeze does not matter if there are 50 members in the population or 100 members. The freeze will affect the entire area 4 DIFFERENT T YPES OF POPULATION CHANGE OCCUR IN NATURE Stable- population size slightly fluctuates above and below (k) Ex. Species in undisturbed tropical rainforests Irruptive Population surge, followed by crash Common of short-lived rapidly reproducing organisms Cyclic fluctuations, boom-and-bust cycles Top-down population regulation Bottom-up population regulation Irregular- no particular pattern POPULATION CYCLES FOR THE SNOWSHOE HARE AND CANADA LYNX Cyclic fluctuation patterns Fig. 5-18, p. 118 ESTIMATING POPULATION SIZES Scientists need to consider several limitations when attempting to estimate population sizes Mobility/immobility Distribution patterns Migration rates Some methods scientist use to estimate ecological populations: Random Sampling (best for stationary organisms) Normally use quadrats Mark Recapture MARK RECAPTURE P=(M*C)/R P= estimated population size M=# of 1 st Sample that were marked C= Total number caught in 2 nd sample R= # recaptured (marked) found in sample 2 MARK RECAPTURE EXAMPLE A biologist caught 16 cichlid species from a lake and tagged all of them. He released them back into the lake. A week later, he went back and caught 13 cichlid fish in the same lake and found that 4 of them were tagged individuals he had recaptured. The estimated population of cichlids in the lake would be: M=16 C=13 R=4 P= (16*13)/4= 52 This method helps with estimating mobile species population sizes RANDOM SAMPLING EXAMPLE 10 8 Since the area is 4x4, take 4 samples Find the average number of individuals per square 4 7 Multiply is times total number of area (16) Total Sampled = 29 Average/sample = 7.25 Est. Population = 7.25*16 = 116 This method is best for evenly dispersed, stationary populations… why? HUMANS ARE NOT EXEMPT FROM NATURE’S POPULATION CONTROLS Ireland Potato crop in 1845 Bubonic plague Fourteenth century AIDS Global epidemic 5-3 HOW DO COMMUNITIES AND ECOSYSTEMS RESPOND TO CHANGING ENVIRONMENTAL CONDITIONS? Concept 5-3 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 Ecological succession: The normally gradual change in species composition in a given area after the area has been disturbed o destroyed in some way Response to such instances as Fire Volcanic eruption Climate change Clearing of forests 2 types: Primary succession Secondary succession SOME ECOSYSTEMS START FROM SCRATCH: PRIMARY SUCCESSION Establishment of biotic community in a lifeless area No soil in a terrestrial system No bottom sediment in an aquatic system Takes hundreds to thousands of years Need to build up soils/sediments to provide necessary nutrients Pioneer species: first species to inhabit the area Examples: Moss, Lichens Occurs after such instances as Volcanic eruption Retreating glaciers Abandoned highway/parking lot Newly created or shallowed pond/reservoir PRIMARY ECOLOGICAL SUCCESSION Fig. 5-19, p. 119 SOME ECOSYSTEMS DO NOT HAVE TO START FROM SCRATCH: SECONDARY SUCCESSION Some soil remains in a terrestrial system Some bottom sediment remains in an aquatic system Much more common than primary succession Restoration is also much faster than in primary succession Occurs after disturbances such as Abandoned farmland Burned/cut forests Heavily polluted streams Flooded land NATURAL ECOLOGICAL RESTORATION OF DISTURBED LAND Fig. 5-20, p. 120 SECONDARY ECOLOGICAL SUCCESSION IN YELLOWSTONE FOLLOWING THE 1998 FIRE Fig. 5-21, p. 120 ECOLOGICAL SUCCESSION SUCCESSION Primary and secondary succession Tend to increase biodiversity Increase species richness and interactions among species Important natural service Both (primary and secondary) are examples of ecological restoration 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 One set of species makes an area more suitable for other species and less suitable for itself Inhibition Early species hinder the establishment of other species growth Succession can proceed when these species are removed Tolerance Plants in the late stages of succession are unaffected/no direct competition with earlier species SUCCESSION DOESN’T FOLLOW A PREDICTABLE PATH Traditional view- Equilibrium Balance of nature and a climax community Climax community: dominated by few long-lived plant species and is in balance with its environment Current view Ever-changing mosaic of patches of vegetation Reflects on-going struggle by species Mature late-successional ecosystems State of continual disturbance and change LIVING SYSTEMS ARE SUSTAINED THROUGH CONSTANT CHANGE Stability is achieved through change Environment is constantly changing, thus to keep it stable, living systems must parallel the change by change 2 aspects of stability: 1. Inertia (persistence) Ability of a living system to survive moderate disturbances 2. Resilience Ability of a living system to be restored through secondary succession after a moderate disturbance Some systems have one property, but not the other SOME ECOSYSTEMS HAVE ONE OR THE OTHER: RESILIENCE OR INERTIA Ranforests (example) High Inertia High resistance to change due to species diversity and richness Once severely damaged, have low resilience Reaches ecological tipping point Grasslands (example) High Resilience Low species diversity makes them susceptible to destruction Because most plant matter stored in underground roots, they may recover quickly via secondary succession THREE BIG IDEAS 1. Certain interactions among species af fect their use of resources and their population sizes. 2. There are always limits to population growth in nature. 3. Changes in environmental conditions cause communities and ecosystems to gradually alter their species composition and population sizes (ecological succession).