population dynamics chapter 8. sea otter – the other, other white meat why are sea otters...

Population Dynamics

Chapter 8

Sea Otter – the other, other white meat

Why are sea otters considered keystone species?They control urchin populations which feed on kelp, hence they keep the kelp forests healthyWhy did their populations decline?Originally due to hunting, now chemical pollution is suspected

Characteristics of a populationSize – number of organismsDensity – number /spaceDispersion – spatial distributionAge distribution – pre-breeding, breeding, or post breeding age

Population dynamics – how these factors change due to environmental stresses

Population growthPopulation change (growth) = (births + immigration) – (deaths + emigration)

ZPG – zero population growth is when incoming equals outgoing

Biotic potential – max growth for that particular populationIntrinsic rate of increase – rate of growth with unlimited resources

High intrinsic growth ratesReproduce early in lifeHave short time between generationsReproduce many timesHave many offspring each time

Roaches, mice, fish, flies

Environmental ResistanceThese are the vast assortment of environmental factors which help keep populations from growing out of control

This is a way a population finds an equilibrium point

Fig. 9.3, p. 200

POPULATION SIZE

Growth factors(biotic potential)

Favorable lightFavorable temperatureFavorable chemical environment(optimal level of critical nutrients)

Abiotic

BioticHigh reproductive rate

Generalized niche

Adequate food supply

Suitable habitat

Ability to compete for resources

Ability to hide from or defendagainst predatorsAbility to resist diseases and parasitesAbility to migrate and live in other habitatsAbility to adapt to environmentalchange

Decrease factors(environmental resistance)

Too much or too little lightTemperature too high or too lowUnfavorable chemical environment(too much or too little of critical nutrients)

Abiotic

BioticLow reproductive rate

Specialized niche

Inadequate food supply

Unsuitable or destroyed habitat

Too many competitorsInsufficient ability to hide from or defendagainst predatorsInability to resist diseases and parasitesInability to migrate and live in other habitatsInability to adapt to environmentalchange

Carrying capacityBiotic potential and environmental resistance will determine the population a given area can hold and sustain indefinitely

A population must not drop below the minimum viable population or lowest number needed to keep population from disappearing due to environmental resistance

Fig. 9.5, p. 201

2.0

1.5

1.0

.5

Nu

mb

er o

f sh

eep

(m

illio

ns)

1800 1825 1850 1875 1900 1925

Year

Logistic growthExponential growth (J curve) is not possible forever because resources and space eventually run out. When a population reaches a certain point, environmental resistance increases causing the population size to stabilize. This is known as logistic growth (s curve) and this generally happens to all populations

Fig. 9.4, p. 201

Time (t) Time (t)

Po

pu

lati

on

siz

e (N

)

Po

pu

lati

on

siz

e (N

)

K

Exponential Growth Logistic Growth

Can you overshoot your carrying capacity?

Absolutely, it happens all the time

When you have too many individuals for the area to support you will have a population crash

If the overshoot was not too drastic, and the crash was small the population re-stabilizes

Types of population curvesStable – nearly flat lineIrregular – widely fluctuating pattern with no periodicity Cyclic – regular growth and crash at set intervals, usually seasonalIrruptive – normally stable, but with a random spike or crash

Fig. 9.7, p. 202

Nu

mb

er o

f in

div

idu

als

Time

Irruptive

Stable

Cyclic

Irregular

Top-down or bottom-up?Evidence seem to show both happening

Top-down – predators hunt and kill prey keeping their population stable

Bottom-up – prey are the food source that allow predators to keep the populations up

Types of reproductionAsexual – cloning, single parent donates both parts of DNA (bacteria)

Sexual – two parents donate DNAFemales have to give birth more (males do not as in asexual)More genetic errors from combiningMating is more damaging, and energy intensiveDoes provide more genetic diversity, hence a stronger species

R-selected speciesAlso known as r-strategists and fill generalist nicheHave many offspringReach reproductive age earlyShort time between generationsLittle to no parental care and adapted to unstable climate (low survivorship)Short life span (usually under a year)Algae, rodents, bacteria, annual plants and insects

Fig. 9.10a, p. 205

r-Selected Species

cockroach dandelion

Many small offspringLittle or no parental care and protection of offspringEarly reproductive ageMost offspring die before reaching reproductive ageSmall adultsAdapted to unstable climate and environmental conditionsHigh population growth rate (r)Population size fluctuates wildly above and below carrying capacity (K)Generalist nicheLow ability to competeEarly successional species

K-selected speciesK-strategists or competitors, specialist nicheFewer, larger offspring (usually develop inside)Mature slowly (often protected while vulnerable)Lower population growth rateLong lived with stable population near carrying capacityDepend heavily upon suitable habitatLarge mammals, birds of prey, long lived plants such as oaks, redwoods, some cacti

Fig. 9.10b, p. 205

Fewer, larger offspringHigh parental care and protection of offspringLater reproductive ageMost offspring survive to reproductive ageLarger adultsAdapted to stable climate and environmental conditionsLower population growth rate (r)Population size fairly stable and usually close to carrying capacity (K)Specialist nicheHigh ability to competeLate successional species

elephant saguaro

K-Selected Species

Survivorship curveLate loss - typical for k-strategistsEarly loss – typical for r-strategistsConstant loss – for species in the gray area in-between k and r strategists with intermediate reproductive patterns

Song birds, lizards, and small mammals

Fig. 9.11, p. 206

Per

cen

tag

e su

rviv

ing

(lo

g s

cale

)

100

10

1

0

Age

Conservation biologySensible use of natural resourcesOriginated in 1970’s – uses current scienceInvestigate human impact on the biodiversityDevelop practical approaches to maintain biodiversityMaintain – endangered species, wildlife reserves, ecological restoration, ecological economics, environmental ethics

Assumptions of conservation bioBiodiversity is necessaryHumans should not affect extinction or vital environmental processesProtecting ecosystems is the best way to protect

Based on Aldo Leopold’s ethical principle, that if we maintain the earth’s life-support system it is appropriate

Human impact on ecosystemsFragmentation – breaking up large tracts with roads, fences, towns, etc.Habitat loss/degradation – pollution, lumber, mining, etc.Simplifying ecosystems – lower biodiversity through habitat change (monocultures)Strengthening species – pesticide use, antibiotics

Human impact continuedPredator elimination – wolves, coyotes, bear, etc.Introduce alien speciesOverharvest potentially renewable resources – trees, soil, other biomass (grasses, nuts, etc)Interfere with natural chemical cycling – clear cutting, monocultures, pesticides (we kill and simplify a system)

Way to go humans!! You’re the best!Goals for the future (if we want to be a part of it)

Maintain balance between human impacted simple ecosystems and natural rich ecosystemsSlow down rates at which we alter nature for our own purposeRealize that we never do merely one thing, everything is interdependent and unpredictable

How can you helpUse consumer power – buy products that are friendly to the environmentUse voting power – elect officials that will strive to protect the environmentEducate – most people have no idea about the consequences of their actionsIdentify “mother culture” that says spend, buy, consume and learn to tune it outExploit nature for its aesthetics and renewable resources

That’s all folks

Have a nice day