Chapter 5: Biodiversity, Species Interactions, & Population Control
Southern Sea Otter
 16-17,000 historically along Cali coast
 Hunted for furs & b/c they compete for game fish
 Nearly went extinct; recovering
 Slow Comeback
o Low biotic potential (1 pup a yr)
o Orca food
o Cat parasites from runoff
o Thorny-headed worms from birds
o Toxic algae blooms
o PCBs & other toxins
o Oil spills
 Who Cares about Otters?
o Heavy tourist draw
o Keystone for kelp forest
 Support hundreds of species
 Algin from kelp for toothpaste, cosmetics, ice cream, & much else
Interspecific Interactions
 Relationships b/w different species
 Affect survival & reproduction of each species
 Effects noted as positive (+), negative (–), or no effect (0)
 Interspecific Competition
o (–/–) interaction
o Species compete for a limiting resource
 Not necessarily fighting
 2 species eating same food
o Competitive Exclusion Principle
 Idea that no two species occupy exact same niche
 One will have advantage over other & eliminate it
 Loser migrates, adapts, or dies
o Realized niche
o Resource Partitioning
 Reduces niche overlap
 Use resources at different times, different ways, or in different places
 Predation
o (+/–) interaction
o Predator kills & eats prey
 Claws, teeth, fangs, stingers, poison, eyesight, speed, camouflage
o Herbivory also Predation
o Prey’s Defense
 Physical – porcupine quills
 Chemical – produce or acquire toxins, bad smell
 Behavioral – hiding, fleeing, forming herds/schools, self-defense, & alarm calls
o Mimicry & Coloration
 Cryptic coloration – camouflage
 Aposematic coloration – warning colors
 Batesian mimicry – good mimics bad
 Mullerian mimicry – bad mimics bad
o Coevolution
 Two interacting species can drive evolution of each other
 Evolutionary arms race b/w predator & prey
 Parasitism
 Bats & Moths
 Bats use echolocation
 Moth uses evasive maneuvers when it hears bat
 Bat changes frequency
 Moth make clicks to jam bat’s radar
 Bat stops making noise, listens for moth’s clicks
 Symbiotic Relationships
o Parasitism
 (+/– ) interaction
 Parasite feeds on the body of, or energy from host
 Endoparasites – live within body of host
 Ectoparasites – live on outside of host
 Coevolution
o Mutualism
 (+/+) interaction
 Nutrition/protection
 Gut inhabitants
 Nutrition/reproduction
 Rhino & Oxpeckers
 Cattle Egrets & Water Buffalo
 Clownfish & Sea Anemone
o Commensalism
 (+/0) interaction
 One benefits, other unaffected
 Bird Nest in Tree
 Epiphytes (air plants)
 Live on stems of other trees
Population Dynamics
 Studies size, density, dispersion (distribution), & age structure of populations
 Dispersion
o Environmental & social factors influence spacing of individuals in a population
o Clumped Dispersion
 Individuals aggregate in patches
 Most common type
 May be influenced by resource availability & behavior
 Reproduction (more partners)
 Hunting (wolves)
 Food source (plants, fungi)
 Protection (fish)
o Uniform Dispersion
 Individuals are evenly, uniformly, distributed
 May be influenced by social interactions
 Territoriality – animals defend area against others
 Plants secrete chemicals to prevent crowding
o Random Dispersion
 Position of each individual is independent (random) of other individuals
 Least common
 Occurs in absence of strong attractions or repulsions
 Population Size
o Effected by…
 Resource availability
 Temperature
 Disease organisms
 Harmful chemicals
 Arrival or disappearance of competitors
o Determining Population Size
 Count all individuals in population
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Sampling techniques
 Count individuals in several different areas, calculate density, then total population
 Count nests or tracks in area, calculate density, then total population
 Mark Recapture Method
 Capture & mark a random sample of individuals
 Release; allow time for mixing
 Capture 2nd set of individuals, count number marked
 Calculate total population
 Practice Problem
 Dolphins – 180 marked initially, 44 recaptured, 7 marked
o Total Population = 1131
 M1 /N = M2 /n (or N = M1 n/ M2)
o M1 = # originally marked
o N = total population size
o M2 = # marked in recapture
o n = total # recaptured
o Population Changes
 Birth Rate
 Death Rate
 Immigration Rate – coming
 Emigration Rate – going
 Total Population change = (Birth + Immigration) – (Death + Emigration)
 Natural Population change = Birth - Death
 Example
 Birth = 25/1000
 Immigration = 10/1000
 Death = 10/1000
 Emigration = 5/1000
 Total Growth Rate per year?
o 20/1000
 If total population = 100,000; how many new individuals in next year?
o 2,000
 Example
 Birth = 24 per 1,000
 Death = 8 per 1,000
 What is natural annual percent increase?
o 16 per 1,000 or 1.6%
o % means 100 in denominator
Population Age Structure
o Proportion of individuals at various ages
 Pre-reproductive age
 Reproductive age
 Post-reproductive age
Biotic Potential
o Capacity for population growth under ideal conditions
o Intrinsic Rate of Increase (r)
 Max rate at which population would grow w/ unlimited resources
o High r values:
 Reproduce early in life
 Short generation times
 Reproduce many times in life
 Large # of offspring each time
Environmental Resistance
o Combo of all limiting factors of population growth
o Carrying Capacity (K)
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 Max population a habitat can support w/o degradation
Growth Curves
o Logistic Growth (S curve)
 Fast growth; then fluctuates around (K)
o Exponential Growth (J curve)
 No limitations
o Thomas Malthus (1766-1834)
 An Essay on the Principle of Population (1798)
 Population growth will lead to starvation, war, disease
 Death rates will check population unless birth rates lower
(K) & Population Crash
o Reproductive time lag leads to overshoot of (K)
o Dieback occurs; can also lower (K)
o (K) can change (seasons, rain drought, competitors)
Survivorship Curves
o Type I – high survival rates when young & decrease sharply when old
o Type II – survival rates are equivalent regardless of age
o Type III – high death rate when young & survival rates higher when older
r-selected Species
o Opportunists; reproduce & spread fast
 Small size, fast growth, short life, many offspring, no parental care
K-selected Species
o Competitor; live in places near max (K)
 Large size, slow growth, long life, few offspring, parental care, strong competitor
Small populations & Genetic diversity woes
o Genetic Problems
 Increase frequency of genetic defects
 Less diversity to adapt
 More susceptible to disease
o Examples
 Founder Effect
 Few individuals from a population colonize a new habitat
 Demographic Bottleneck
 Few individuals survive a catastrophe
 Genetic Drift
 Random changes in gene frequency
 Some individuals may breed more often than others; their genes become more
prevalent
 ‘Flip a coin’
 Inbreeding
 Close relatives mate
 Lines up recessive genes
 Greatly increases risk of genetic abnormalities
o Minimum Viable Population Size
 Minimum size of population needed for long term survival of a species
 These ideas w/ island biogeography model help to predict
Population Density
o Density Dependent Factors
 Larger effect w/ higher density
 Predation
 Parasitism
 Disease transmission
 Competition for food, space, mates
o Density Independent Factors
 Density doesn’t matter
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Normally abiotic factors
 Floods
 Hurricanes
 Fire
 Pollution
 Habitat Destruction
 Severe cold/warm weather
 Human Controls
o Bubonic plague (1300s)
 Bacteria from rat fleas
o Ireland (1845)
 Potato rot from oomycete
o AIDS
 Viral STD
 White-Tailed Deer
o Deer in U.S.
o 1900 – habitat destruction & uncontrolled hunting
o 1920s-30s – laws to protect deer; wolves & mountain lions nearly eliminated
o Current – 25-30 mil. deer
 Lyme disease carrier
 Deer-vehicle accidents (1.5 mil.)
 Eating garden plants & shrubs
o Hunt ‘em down
o Hunted in rural areas
 More doe tags given to lower #s
o Suburbs?
 Can’t have gun nuts running around
 Hired professional archers
 Fence in yards
 Spray predator scent
 Birth control & sterilization?
Ecological Succession
 Gradual change in community composition in a given area over a long period of time
 Just a GENERAL pathway
 Two types…
o Primary Succession
 Begins in lifeless areas w/ no soil
 Areas such as…
 Lava Flow
 Receding Glacier
 Abandoned Road/Parking Lot
 Takes a long time b/c no soil
 Rock breaks down & releases nutrients by…
o Physical weathering – water
o Chemical weathering – rain water & atmospheric compounds
o Biological weathering…
 Early Successional Plants
o Pioneer species attach to weathered rocks
 Arrive as seed/spore brought by wind or animal
 Lichens – mutualism b/w alga (photosynthesis) & fungus
(protection)
 Mosses – primitive plants
o Pioneers Create Soil
 Trap wind blown particles/detritus
 Secrete mild acids that further breakdown rocks (lichens)
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 Mosses trap water like a sponge
 Waste & dead matter from pioneers
 After 100s-1000s yrs; soil may be thick & fertile enough for…
 Midsuccessional Plants
o Herbs, grasses, & low shrubs
 Create shade; kills off lichens & mosses
o Trees adapted to area arrive
 Fast growing, shade intolerant
 Climax or Late Succession
o Shade tolerant seedlings arrive
 Tall trees w/ long life spans
o Mid-successions dieoff b/c seedlings shade intolerant
Secondary Succession
 Occurs after disturbance, removal, or destruction of ecosystem
 Still has soil left
 Beginning Anew
 Seeds germinate that remain from before disturbance, or are brought from
elsewhere
 Much faster than primary b/c soil already present
Succession Setbacks
 Fires
 Hurricanes
 Clear-cutting of forests
 Plowing of grasslands
 Invasive species
Prescribed Burning
 Natural habitat not always climax community
 Periodic fires can keep out late succession plants
 Gets rid of fast burning plants
 Small weeds & scrub brush
 Maintains high native biodiversity
 Florida Long Leaf Pine
 150 yrs to reach 100+ feet tall adult
 Live up to 500 yrs
 Very Fire Resistant
o Thick layers of bark
o Leaves occur high off ground
o Needle-like leaves
o Leaves contain tannic acid
 Red-Cockaded Woodpecker, Gopher Tortoise, Indigo Snake