Population Ecology Dynamics of Ecosystems

Individual Population Community Ecosystem Biome Biosphere

I.  Ecological    

Hierarchy

II. Population: same species living in an area } Species = group of similar organisms that can

interbreed } Example: all the Giant pandas in a forest

III. Community: group of different populations living in same area

} Example: All the different plants & animals in a forest with the panda

}  Definitions } Population Ecology: major sub-field of

ecology that deals with dynamics of species populations & how these pops interact with the environment

} Population Dynamics: studies short- and long-term changes in size, density & age distribution of pops, and the biological and environmental processes influencing those changes ¨ Birth and death rates ¨ Immigration and emigration ¨ Pop decline

Uniform  –  helps  reduce    intraspecific  competition  

•  Population Distribution aka Dispersion:

Clumped–  helps  w/  protection  

Random  –  seen  in  some  plants  

•  Population Size o Changes with 4 variables: 1. Births 2. Deaths 3. Immigration 4. Emigration

•  Pop change = (Birth + Immigration) – (Death + Emigration)

•  Age structure also influences pop change o  = Numbers of prereproductive, reproductive, &

postreproductive individuals

•  Biotic potential = Populations vary in their capacity for growth o  Intrinsic rate of increase (r) = rate of pop growth w/ unlimited resources

•  A pop with few resource limitations will grow exponentially (J-shaped curve): o  *Humans

} Most pops grow < intrinsic rate of increase (r) b/c of environmental resistance

}  Environmental resistance: all factors that act to limit pop growth }  Can be Abiotic or Biotic

}  Can be Density-independent or Density-dependent

https://www.youtube.com/watch?v=QI2ixJeIxEU Serious Science Biological Carrying Capacity

}  Density-independent factors

= Any factor in the environment that does not depend on the number of members in a population per unit area

Weather events

Fire

Human alterations of the landscape Air, land, and water pollution

}  Density-Dependent Factors

Any factor in the environment that depends on the number of members in a population per unit area

Predation

Disease

Competition

Parasites

•  Biotic Potential vs. Environmental Resistance o  Generally come to

some equilibrium:

•  Carrying Capacity (K)

•  = max number of individuals of a given species that can be sustained indefinitely in a given space

o = equilibrium b/w biotic potential and environmental resistance

•  Populations w/ a carrying capacity show logistic growth (S-shaped curve): o  Start off with rapid exponential growth o  Followed by a steady decrease at K

•  Logistic Population Growth:

}  Some organisms overshoot carrying capacity à results in a pop crash (dieback) }  Due to reproductive time lag (period needed for birth rate to fall & death

rate to rise in response to resource overconsumption) Tasmanian Sheep Alaskan Reindeer

•  There are 4 Types of Population Change Curves

}  4 Types of Population Change Curves 1.  Stable: stay generally around K

}  Seen in consistent environments like tropical rain forests

2.  Irruptive: stay stable except for occasional peaks & crashes

}  Seen in insects & algae (in temperate climates); raccoon & house mice

3.  Cyclic: regular fluctuations }  Seen in lemmings; lynx & hare

4.  Irregular: no pattern

•  Predator & Prey Population Cycles o  Pop cycles of predator influence pop cycles of prey & visa-versa o  Examples: Lynx & Hare; Wolf & Moose** (**worksheet)

•  Sexual Strategies & Patterns:

•  Asexual reproduction: does not require sex cells (gametes). Aka Mitosis – cloning. o Bacteria reproduce this way. Only 3% of all species use

this form

•  Sexual reproduction: requires gametes à results in genetic recombination

Disadvantages

½ pop doesn’t give birth Increased chance of genetic defect/error

Courtship and mating rituals can be complex

Advantages

Genetic variety/diversity!! Parents can divide responsibilities

•  Sexual Strategies & Patterns: o  Reproductive Patterns: 2 types

•  Classification of species’ reproductive pattern depends on their position on the population growth s-curve

o r-selected species

o K-selected species

https://www.youtube.com/watch?v=Bu6ouKt9zhs Bozeman Science

•  r- selected species/ Opportunists o  Capacity for high rate of pop increase o  Reproduce early o  Many, small offspring

•  Most don’t survive o  No/ little parental care o  Generalist niche o  Examples:

•  Algae •  Bacteria •  Rodents •  Insects •  Annual plants

•  K-selected species/ Competitor o  Show lower pop growth rate o  Reproduce late in life o  Few, larger offspring o  More parental care o  Specialist niche o  Do well in competitive situations, with stable

env conditions o  *Prone to extinction o  Examples:

•  Large mammals •  Birds of prey •  Large, long-lived plants

•  Different reproductive strategies have different types of survivorship: o  = percent of individuals surviving to certain ages

•  3 Types of Survivorship Curves:

•  3 Survivorship Curves:

•  Type I: Late Loss o Low infant mortality & long life spans o Tend to be K-selected species o Examples: humans (in developed countries); large mammals

(elephants, big cats, etc.)

•  Type II: Constant Loss o Death rate even among all ages o Examples: some birds, some invertebrates, rodents

•  Type III: Early Loss o High infant mortality and then constant mortality for few remaining o Seen in most r-selected species o Examples: annual plants, small fish, marine invertebrates, insects

Community Ecology How do organisms interact?

Community Ecology •  Community Structure is based on:

1.  Physical Appearance: size & distribution of its populations

2.  Species Diversity: combination of o Species richness: # of different species o Species evenness: abundance of individuals within each

species

3.  Niche structure: # of niches and species interactions

•  Species Equilibrium Model (E.O. Wilson)

•  aka Theory of Island Biogeography

o Balance b/w 2 variables determines the number of different species found on an “island”:

•  rate at which new species immigrate to the island •  rate at which existing species become extinct on the island

•  3 factors must be taken into account:

1. Immigration and extinction rates 2. Island size 3. Distance from “mainland”

Useful when protecting wildlife on “habitat Islands” a.k.a areas surrounded by development

Remember the Major Roles that Species Can Play within Ecosystems cont.:

1.  Native 2.  Nonnative (Invasive) 3.  Indicator 4.  Keystone 5.  Foundation species

SE Asia Durian Fruit & Bats (a.k.a Flying Foxes)

Endangered due to 1.  hunting for their meat 2.  Deforestation 3.  Targeted to keep them from eating commercially grown fruit

Keystone 1.  sustains tropical community 2.  pollinates many plant species 3.  disperses seeds in droppings & therefore maintains forest biodiversity

Mutualism (+, +)

https://www.youtube.com/watch?v=69IGcIp-AZg

•  Invasive Species •  1957 Brazil imported African

Bees for honey production, instead they displaced domestic bees and reduced honey supply

•  They have since moved north & reached the United States

•  They are aggressive & unpredictable, kill 1000’s of domesticated livestock and about 1000 people due to allergies

•  So far winter stops them from spreading farther north https://www.youtube.com/watch?v=y7C--Cv4gPw

Indicator Species

Species What  do  they  Indicate?

Trout Water  Quality;  require  clean  water  w/high  D.O.  

Birds  &  BuAerflies Chemicals  &  habitat  loss;  found  everywhere

Amphibians  (frogs,  salamanders,  &  toads

Pollutants  in  air,  water,  &  soil,  UV  light,  habitat  loss  (filling  in  wetlands),  drought,  overharvesting; Live  in  water  as  herbivores  &  as  adults  on  land  as  carnivores,  thin  permeable  skin,  eggs  have  no  protection,  

https://www.youtube.com/watch?v=BvidpapF1bg Sci Show https://www.youtube.com/watch?v=1q5oe33M15Q Scary Bat Die off http://www.smithsonianmag.com/videos/category/wildlife/saving-amphibians-from-deadly-fungus/ Amphibian Chytrid Fungus

Keystone & Foundation Species: American Alligator hunted for meat, skin, and/or for sport 1950-1960 90% decline in LA 1967 put on endangered species list 1977-1987 upgraded to threatened list in 8 states Keeps areas free of vegetation, digs deep depressions that fill with water & serve as refuge for aquatic life, feed on predatory gar https://www.youtube.com/watch?v=_IWw8Ruz8Uo

Keystone Species and their Role 3:59 https://www.youtube.com/watch?v=0-PE3ve3w2w Bozeman Science 7:35

Species Interactions:

Competition= occurs between two species for resources (food, space, etc.)

Gause’s principle states that no 2 species can occupy same niche at same time à 1 species must relocate, die out or change niche Over a time scale long enough for natural selection, Resource Partitioning can occur:

Species minimize competition by filling specific niches within an ecosystem (traits allow them to utilize resources at different times, locations or ways)

Ex: North American warblers hunt for insects in same spruce trees, but at different parts & times

Symbiotic Relationships An interactive association between two or more species living together Predation (+, -) Interaction b/w organisms in which one organism (predator) captures and feeds upon another (prey)

Preys’ Defense Mechanisms: Physical adaptations: highly developed sight & smell; shells; spines; thorns; Camouflage & mimicry

Chemicals: poisons, irritants, odors, ink clouds Behaviors: puffing up, mimicking a predator, playing dead

Hognose snake

Praying mantis

Cuttlefish

Parasitism: when one organism (parasite) feeds on or otherwise harms another organism (host) in close association (+,-) Different from predation in that parasite is generally smaller than host and doesn’t kill host, but harms over time

Brood parasitism Mistletoe Tick (Ectoparasites)

Video: https://www.youtube.com/watch?v=XuKjBIBBAL8 David Attenborough Parasites

Commensalism: benefits one species but has little or no effect on other species (+, 0)

Epiphytes (Bromeliads & some Orchids)& Trees

Whales & Barnacles

Mutualism: interaction benefitting both species (+, +)

Pollination Mutualism Nutritional Mutualism: Lichen (fungi & algae)

Gut Inhabitant Mutualism

All communities change their structure & composition over time in response to each other & changing environmental conditions Disturbances: change in environmental conditions that disrupts a community or ecosystem. These disturbances can range from mild to catastrophic and can be caused by natural occurrences or human activities:

Ecological Succession = gradual change in species composition

Two Types:

•  Primary Succession

•  Secondary Succession

•  Primary Succession: the gradual establishment of biotic communities on lifeless ground (rock)

Pioneer Species (Lichens, Algae, Bacteria, Moss)

Pioneer Species start soil formation process: trap soil particles & detritus in wind, secrete acids to break down rock

Late successional species

Mid successional species

End in Mature Community (long-lived hardwoods)

•  Secondary Succession: when biotic communities are established in an area where some type of biotic community is already present

•  Occurs after disturbance (burned forest, polluted stream, abandoned farmland)

•  Intermediate Disturbance Hypothesis: communities that experience fairly frequent but moderate disturbances have the greatest species diversity

Succession Model Online •  http://www.mrphome.net/mrp/succession.swf

•  Measuring Biodiversity o Shannon’s Diversity Index (H): range from 0 to 5

(more diverse) o Simpson Diversity Index (D): range from 0 (zero

diversity) to 1 (infinite diversity)

•  Shannon’s Diversity Index

H = the Shannon Diversity index Pi = fraction of the entire population made up of species i (ni/total) S = numbers of species encountered ∑ = sum from species 1 to species S

s H = -∑ (Pi * ln Pi)

i=1

•  Simpson Diversity Index

D = the Simpson Diversity index ni = number of individual per species N = total number of individuals S = numbers of species encountered ∑ = sum from species 1 to species S

s D = 1 -∑ [(ni / N) 2]

i=1

•  Shannon’s Diversity Index

•  High values of H would be representative of more diverse communities. •  If the species are evenly distributed then the H value would also be high.

So the H value allows us to know not only the number of species but how the abundance of the species is distributed among all the species in the community.

Birds Ni Pi ln Pi - (Pi * ln Pi) Pigeon 96 .96 -.041 .039 Robin 1 .01 -4.61 .046 Starling 1 .01 -4.61 .046 Crow 1 .01 -4.61 .046 House Sparrow 1 .01 -4.61 .046 H  =  0.223