Ecology - Population Ecology, Community Ecology, Ecosystems and the Biosphere
General Biology BI 04 Summer School Lecture Notes



Definition - study of the interaction between organisms and their environment, environment composed of abiotic and biotic factors

Abiotic component - soil, altitude, climate (temerpature, humidity, wind, etc.), latitude, other

Biotic component - predators, prey, parasites, competitors, other

Major Areas of Ecology

Population Ecology

study of population growth and factors that affect growth

Community Ecology

study of interactions among species, ecological succession

Ecosystems and the Biosphere

study of cycling of materials and energy through ecosystems

Population Ecology

Study of distribution, density, numbers of individuals and structure (gender, age), rates of natality and mortality, factors that affect growth


group of individuals belonging to the same species that inhabit a specific geographic location at a specific point in time

Characteristics of Poplations

Density - number of individuals/per unit area (e.g., per acre or hectare) or unit volume (e.g. in a column of water)

Spacing - dispersion

Density and numbers

Counting individuals to determine density and population size

rarely able to count the entire population, instead - count all the individuals in a prescribed area

1) Simple counts (# seals/island, # burrows/area, # wildebeest/herd

2) Mark-recapture technique

capture individuals

mark individuals

recapture at a later point in time - provide estimate of population size for a given area

calculation = (total number marked)(total number recaptured)/(number of recapture that were marked)


initial capture of 50 individuals

second capture of 100 individuals, 10 of the 100 were marked from the first capture

estimated popultion size = 50(100)/10 = 500 individuals

3) Census techniques - transect methods, walk or drive a line (transect) and count the number of individuals at specific locations, evenly distributed along the line


Type of Distribution Example Possible Explanations of Distribution
Clumped patchy distribution of resources
Uniform terrritorial species
Random random distribution of resources


Demography - study characteristics of a population that affect growth


follow a cohort (group of individuals from birth to death) over time

construct a life table for the cohort - see example below

Age Class Number of Survivors Number of Deaths Mortality rate
0.000 = 0/11
10-19 10 1 0.090 = 1/11
20-29 8 2 0.200 = 2/10
30-39 7 1 0.125 = 1/8
40-49 5 2 0.286 = 2/7
50-59 3 2 0.400 = 2/5
60-69 2 1 0.330
70-79 2 0 0.000
80-89 1 1 0.500
90-99 0 1 1.000
100+ 0 0 1.00

Calculate Rates for Populations

3 rates

Survivorship - number of individuals that reach the next year of life

Birth - number of inidivuals born/designated time frame

Mortality - number of individuals that die each year

Study survivorship - number of survivors/age group, yields 3 different curves



Type I - high survivorship for most age groups except older individuals (humans, large mammals, organisms that produce few offspring but provide extensive parental care)

Type II - constant survivorship rate for most age groups (some species of birds, lizards, annual plants, invertebrates and rodents)

Type III - low survivorship early but individuals that do make it live longer (many species of fish and marine invertebrates, produce many young and no parental care)

Other factors that affect population growth - Life History Traits

Clutch size - number of young produced/reproductive event (small - large)

Number of reproductive episodes/lifetime

iterparous species - mate many times, repeated reproduction

semelparous species - mate once/lifetime, big bang reproduction

Age of reproductive maturity (see above)

some species have delayed maturity, some are born pregnant

Measure/Model Population Growth

N = population size - total number of individuals in a specific area at a given time

B = number of births, b = birth rate

N = 1000

B = 34

b = .034

D = number of deaths, d = death rate

N = 1000

D = 16

d = .016

T = time

r = b-d, rate of increase

Population growth rate under ideal and unlimited conditions, changes over time

Population growth rate that takes into account K - carrying capacity (maximum number of individuals that could occupy a given area, defined by the ability of the resources in the environment to support the population)

Two typical patterns or models

Growth curve, typical of r-selected species, high growth rate, large clutch size, no parental care



Sigmoid growth curve, typical of k-selected species, slower growth rate, small clutch size, extended period of parental care



Allee effect - problems occur in populations that become too small and have fallen below a critical population size, may need a certain number of individuals to stimulate reproduction, especially for solitary species

Population Regulation - 2 factors affect population growth

Density-dependent - depend on the number of individuals in the population

food, mates, increased rates of predation and parasitism, stress and behavioral problems due to overcrowding, available nesting habitat, water, oxygen, waste buildup

Density-independent - do not depend on the number of individuals in the population

weather and climate (drought, typhoon, hurricane, excessive rain or snow, etc...), geological disturbances (earthquake, tidal wave, volcanic eruption, etc.)

Interesting patterns - boom and bust cycles


Snowshoe Hare and Lynx in Canada, Snowshoe Hare populations increase followed by increase in Lynx followed by decline in Snowshoe Hare followed by decline in Lynx followed by increase in Snowshoe Hare .......

Human Populations and the effects of Population Structure

Age - number of individuals/age group

Example - human population pyramids


Undeveloped Countries

(expanding population)

Developed Countries

(restrictive population)

Sex/Gender - number of males and females (number of females tied to number of births)

Generation time - average time from birth to first reproductive event

short - faster population growth

longer - slower population growth

Community Ecology - study of species interactions and interactions with the abiotic environment

2 views of communities

1) individualistic hypothesis - chance occurrence of species with similar habitat requirements

2) interactive hypothesis or superorganism concept - all species are closely tied together and locked into associations, species that make up the community function together as a unit, dependent on each other

Niche - way of making a living

community is composed of many species occupying different niches

multidimensional niche - takes into account all dimensions of how an organism can make a living: time of day an organism is active, food types, nesting preferences, habitat preferences, altitude, etc...)

fundamental niche - all the resources an organism is capable of exploiting

realized niche - all the resources an organism is actually exploits/uses in its environment

Interspecific Interactions between species in a community

Coevolution - reciprocal interactions between species

Arms race between plant/herbivore: Passiflora flowers and Heliconius butterflies: flowers are poisonous to defend against herbivores, butterflies develop resistance .......


Interspecific competition - 2 or more species compete for the same resources

Competitive exclusion - Gause (1934) - laboratory experiment with 2 species of Paramecia (P. aurelia, P. caudatum), P. aurelia outcompeted the P. caudatum and the P. caudatum went extinct

Character or ecological release - species exhibit greater morphological variation in areas that lack competitors (especially marked on islands that lack mainland competitors, sometimes referred to as incomplete biotas)

Van Valen (1965) - measurement variation in bill length and bill width (coefficient of variation) 6 species of birds on islands was greater than variation on the mainland

Melanerpes striatus (woodpecker) in Hispainolo exhibits sexual dimorphism in beak and tongue size but other Melanerpes species on the mainland which coexist with other woodpecker species lack sexual dimorphism (Selander 1966)

Crowell (1962) found that 3 species, Northern Cardinal, Gray Catbird, White-eyed Vireo, all occupied a wider range of habitats and foraging niches than conspecifics on the mainland

Morse (1970) found that the Northern Parula Warbler and Myrtle Warbler expand their habitat utilization and plasticity in foraging in the absence of Black-throated Green Warblers on islands off the coast of Maine

Cocos Finch - on Cocos Island, eats a wider variety of foods and has greater morphological variation than other Galapagos finches on the Galapagos Islands which coexist with other species

Character displacement

Character displacement, term coined by Brown and Wilson (1956), species are different when they are sympatric to avoid competition but allopatric populations are more similar morphologically to each other


Vaurie (1951) studied 2 Old World (East Asia) species of Nuthatches (Sitta tephronota, S. nuemayer) - very similar bill measurements and face pigmentation in allopatry but strikingly divergent in sympatry

Galapagos finches - Geospiza fortis and G. fuliginosa, same beak size (depth) when they are allopatric but have different beak sizes when they are sympatric, G. fortis is larger than G fuliginosa in sympatry (Grant 1986)

Sticklebacks in the W Canada, sympatric species live in lakes and differ in several morphological measurements (gill rakers, body shape, mouth morphology, etc.), in lakes where there is only one species, the measurements are intermediate between those of sympatric species (Schluter and McPhail 1992)



Example 1 of epiphyte climbing a tree (South Portland, Maine, 6 September, 2003)

Exam ple 2 of epiphyte's spindle-like vines (South Portland, Maine, 6 September, 2003)

Example 3 of epiphyte's spindle-like vines (South Portland, Maine, 6 September, 2003)

The Parastic Plant Connection web site


Mutualism - both species benefit by each other's presence

nitrogen fixing bacteria and plants

E. coli living in the intestine of humans

Douglas (1994) - several examples of prokaryotes that invaded and live inside eukaryotes, both species derive some biochemical benefits

Nilsson et al. (1985) - hawkmoth with a long proboscis is a pollinator for a Madagascar white orchid with a long tubular flower, goes for the nectar at the base of the flower

Hummingbirds, Sunbirds, White-eyes, other avian nectarivores, insects, bats and other mammals that feed on plant nectar and spread plant pollen, most species are tropical and prefer one species of plant, prevents crosspollination

Futuyma (1998) - Pseudomyrmex ants that inhabit acacia trees, trees provide housing and food (protein food resources) for the ants while the ants protect the tree by attacking herbivores

Characteristics of a community

Diversity - measured by species richness

number of species

numbers of individuals/ species

Trophic Structure

producers, herbivores, carnivores, saprophytes

Examples of Terrestrial Communities

New Hampshire

Forest and freshwater communities from Mt. Kearsarge (11 May, 2003)

Spruce Forest in spring - Mt. Kearsarge (11 May, 2003)

Spruce Forest in winter - Cannon Mountain (19 March, 2003)


Tropical Fern Forest - near Kilauea Crater, Hawaii (26 May, 2003)

Grassland community - South Point, Hawaii (26 May, 2003)

Examples of Marine Communities

Intertidal Zone - Crescent Beach, Cape Elizabeth, Maine (26 June, 2003)

Least Sandpipers feeding in Intertidal Zone, Kettle Cove Beach, Maine (6 September, 2003)

Examples of Salt Marsh and mud flats in New England

Salt marsh - high tide (South Portland, Maine, 14 September, 2003)

Salt marsh - low tide with mud flats (South Portland, Maine, 14 September, 2003)

Stability of a community over time - ecological succession

succession - process of changing transitional stages that lead to a climax community, each stage contains different species that predictably follow each other

Primary succession - colonization of bare rock or soil

Grasses and Ferns on lava lake - Kilauea Crater, Volcanoes National Park, Hawaii (26 May, 2003)

Several O'hia lehua on lava lake - Kilauea Crater, Volcanoes National Park, Hawaii (26 May, 2003)

Single O'hia lehua on lava lake - Kilauea Crater, Volcanoes National Park, Hawaii (26 May, 2003)

Secondary succession - replacement of one community of species by another through gradual process of colonization


autogenic - changes caused by the organisms that make up the community

inhibition - some species inhibit the growth of others

facilitation - current species modify the landscape and stimulates growth of members of the next community

allogenic - external factors

climate, geological disturbance, fire (some plants require heat and fire for germination, other)

human disturbance - example in tropical rainforests

slash and burn agriculture

timber harvest



results - biodiversity crisis

Global trends in species diversity

Continental pattern - highest in the tropics and decreases towards the poles (birds, mammals, reptiles, insects, flowering plants)

Island patterns

affected by area of the island (larger islands have more species)

affected by the distance from the mainland (more distant islands have fewer species)

affected by speciation rate (if this is low then the number of species will be low)

affected by extinction rate (if this is high then the number of species will be low)

interspecific interactions on islands

predation - rats, cats, mongooses, snakes, Predatory snail on the island of Moorea in the South Pacific caused the extinction of other land snails (Murray et al. 1998)

interspecific competition - 12 species of white-eyes are distributed among islands off Papua New Guinea, no island has more than one species, 3 species of honeyeaters are distributed over the island of Papua New Guinea but only occur in pairs that are separated by altitude (Diamond 1975)


Ecosystems - study of biological communities and their interactions with the abiotic environment (energy and chemical cycling through the ecosystem)

Food chain - ogranized into trophic levels



Energy flow through the ecosystem (conversion of light energy - chemical energy, chemical energy flows through ecosystem)

GPP - gross primary production, total amount of energy from the sun aquired by plants

NPP - net primary production = GPP-plant respiration, incorporated into plant biomass (plant tissues)

Energy traveling through the ecosystem an be expressed in joules/kcal or biomass pyramids, usually less than 20% production efficiency

Comparison of NPP among biomes and habitats

Chemical cycling through the ecoystem and the atmosphere


evaporation from rivers, lakes, streams, ocean leads to condensation into clouds in the atmosphere

rainfall sends water back to earth, picked up by plant tissues, enters ecoystem, remaining water enters the watershed

see diagram


Terrestrial: carbon dioxide in the atmosphere is picked up by plants during photosynthesis, enters the ecoystem, released back into the atmosphere by respiration, burning, volcanic activity, artificial sources: combustion engines, can become buried when organisms die and are covered by sediments, later recovered in the form of coal, oil or natural gas

Aquatic: carbon dioxide diffuses into the water, picked up by marine algae, enters the ecoystem, carbon dioxide released back into the water through respiration, can diffuse back into the atmoshphere, also ends up in sediments due to death of organisms that float to the floor of the ocean


nitrogen is assimilated into plant tissues from nitrogen in the soild or sometimes from the atmosphere with aid of nitrogen-fixing bacteria, enters the ecosystem, leaves the ecosystem through nitrogenous wastes of organisms or death of organisms, denitrifying bacteria can release nitrogen back into the atmosphere, artificial sources - agriculture


phosphorous made available by geological uplifting, makes it into the soil, picked up by plants and enters the ecosystem, death of organisms cause release back into the environment, runoff, sedimentation back to uplifiting, artificial sources - agriculture

Problems with human disturbance

combustion engines - create excess sources of carbon dioxide - results in production of greenhouse gases, greenhouse effect

agriculture - can cause eutrophication of freshwater ecoystems, algal blooms use up all the oxygen and causes death of the ecosystem

other contributions

pesticides - DDT and biological magnification of poisons in the food web

chloro-fluro-hydrocarbons released into the atmosphere cause destruction of the protective ozone layer

thermal pollution - artificial heating of ecosystems


Factors affecting distribution of biomes

temperature and sunlight (angle of the sun and how the sun's rays hit the earth affect heating of the planet)

water and precipitation - ranges from dry to wet areas

wind patterns - affects temperature and water loss

rocks and soil (pH, mineral content, salinity, etc.)


Biomes Physical


Plants Animals
Tundra 2 seasons, dry, frozen deserts, winter:

extreme cold and snow, summer: flooding caused

by snow melt, permafrost layer (permanently

frozen, about 3 m below ground), location: far

north and far south - towards the polar ice caps,

average temperature: 10 degrees celsius

rainfall: 25 cm/yr

snow: 10 - 20 cm/yr

no trees, dominated by mosses and

lichens and grasses, some small


insect blooms, large hooved mammals

(Caribou, Musk Ox), Bears,

wolves, small rodents (lemmings),

migrants during the breeding


Taiga/Boreal Forest long winter, short fall and spring,

2-3 months of summer, wetter seasons,

heavy rain and snow

location: coniferous forest, far nothern and far

southern latitudes

trees 5 - 10 m high,

boreal forest, conifers - pine,

spruce, bog plants (ferns and mosses)

diverse array of migrants from

the tropics with few resident species

(Moose, Bear, Lynx, fox, voles),

large insect blooms

Temperate Deciduous Forest 4 seasons, rainfall: 80-140 cm/yr complex levels of vegetation

deciduous trees, loose leaves

in fall

diverse array of migrants from

the tropics and resident species

Savanna dry, rainfall: 90 - 150 cm/yr

location: tropical to subtropical,

3 seasons

grasses, forbs, trees short and (2m tall)

clumped together (10 m tall)

large ungulates, large predators
Temperate Grassland temperate and some subartic grassland

(extreme northern prairies - steppes and

some extreme southern grasslands -

pampas of Argentina)

rainfall: 25-70 cm/yr

grasses large ungulates
Chaparral mild wet winter followed by hot, dry, summer

many plants dependent on regular fires

associated with Chaparral

location: near coastlines (California, Chile,


short trees and shrubs diversity of mammals, birds,

insects, etc. that like dry


Desert very dry, rainfall: less than 25 cm/yr

location: primarily equatorial but some reach

into temperate regions

cactus, sagebrush, creosote

and shrubs

small rodents, reptiles
Tropical rainforest very wet - heavy rainfall, soil - poor in nutrients,

temperature constant throughouth the year

wet and dry seasons

location: equatorial, 23.5 degree N latitude -

23.5 degree S latitude

large trees- broad-leaved evergreens,

epiphytes, not much forest

floor vegetation (little sunlight).

canopy 30 - 40 m above ground

highest diversity of animals
Aquatic Biome freshwater and marine    
Marine - Pelagic Zone deep ocean, dependent on upwellings algae various birds, large mammals


Marine - Benthic ocean floor, no light none detritus feeders, predatory fish
Marine - Estuaries where rivers flow into the ocean, mix of saltwater

and freshwater, marshes rich in plants and


aquatic vegetation, marsh plants rich variety
Marine - Intertidal zone shoreline to shallow waters algae marine worms, clams, oysters,


Coral reefs tropical oceans algae coral, fish



Conservation Biology
Definition - identification of endangered populations and study of methods/solutions to protect them

Pollution, Development, Harvesting (hunting, commercial exploitation, poaching), Introductions


In situ - conserve land/habitat/ecosystems, legislation and protection (Endangered Species Act, CITES Treaty)

Reserves in Costa Rica

Protected beaches in Pine Point, Maine (4 June, 2003)

Nest enclosure for Piping Plover in Pine Point, Maine (4 June, 2003)

Ex situ - zoo propagation of endangered species, captive breeding programs


Loss of biodiversity - endangered and threatened species

Loss of genetic diversity - losing uniques genes and gene products from these organisms

Examples of human/artificial disturbance to natural populations

Deforestation - practice of clearcutting

Olson (1970s - 1980s) - Polynesians in the southwest PacificEuropean exploitation of North America

Great Auk off the coast of Newfoundland

Dodo of Madagascar

Carolina Parakeet

Passenger Pigeon

Heath Hen


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