Ecology

Ecology: the scientific study of the interactions between organisms and their environment

Ecological Organization (smallest to largest)

Population; all members of a species living in a given location. Ex. Water lilies in a pond, dogwoods in Blacksburg

Community; all the interacting populations in a given area. Ex. Plants, animals, and microorganisms in a pond

Ecosystem; all the members of a community plus the physical environment in which they live. The living and nonliving parts of the ecosystem function together as an interdependent and relatively stable system

Biosphere: portion of the earth in which living things exist. The biosphere, which is composed of numerous, complex ecosystems, includes the water, soil, and air.

Characteristics of Ecosystems

Self-sustaining unit when the following conditions are met:

·        There must be a constant flow of energy into the ecosystem, and there must be organisms in the ecosystem that use the energy for the synthesis of organic compounds

·        There must be a cycle of materials between living organisms and the environment.

 

Abiotic (nonliving) factors

·        Abiotic factors of the environment are physical factors that sustain the lives and reproduction cycles of organisms. These factors are

§         Intensity of light

§         Temperature range

§         Amount of water

§         Type of soil

§         Availability of minerals and other substances

§         Supply of gases, including oxygen, carbon dioxide and nitrogen

§         pH (acidity or alkalinity)

·        Abiotic factors vary from one environmental area to another

·        Determine the type of plants and animals

·        Water and temperature are major factors

Limiting factors: the availability of resources limits the not only the types of plants and animals but also population size

Biotic (Living) FACTORS:

·         all living things that directly or indirectly effect the environment

Nutritional Relationship

Nutritional relationahips involve the transfer of nutrients from one organism to another within the ecosystem

Autotrophs: organisms that can use energy from the environment to synthesize their own food from inorganic compounds

·        Most are photosynthetic

·        Producers

Heterotrophs: cannot synthesize food, must obtain nutrients from other organisms

·        Classified according to source of food

Saprophytes (decomposers); obtain nutrients from the remains of other organisms. Plants, fungi and bacteria

·        Mushrooms obtain nourishment from dead plants

Herbivores: animals that feed on plants

Carnivores: animals that consume other animals

Predators----prey

Scavengers; feed on remains of animals they have not killed

Omnivores: animals that consume both plants and animals

Energy Flow Relationship

For an ecosystem to be self-sustaining there must be a flow of energy between organisms

Food Chains: the transfer of energy from green plants through a series of organisms with repeated stages of eating and being eaten..

·        Organisms in a food chain are described in terms of the following categories

 

Producer         à                 Primary Consumer   à               Secondary Consumer

(grass)                                 (grasshopper)                                (frog)

Trophic Level; feeding levels

Trophic Levels (Trophic Levels 2)

Producers: green plants and other autotrophs. All the energy for community is derived from the organic compounds synthesized by the producers

Consumers: all heterotrophic organisms in a community

Primary Consumer: animals that feed on green plants

Secondary Consumers: animals that feed on primary consumers (carnivores)

Omnivores may be either primary or secondary

Tertiary Consumers: Feed on everything

Includes decomposers

Food Web: most organisms eat more that one species and may be eaten, in turn, my more than one species. Food chains are interconnected forming a food web.

 

 ENERGY PYRAMID

·        The greatest amount of energy in a community is present in the organisms that make up the producer level.

·        Amount of energy passed to the next level decreases

·        A pyramid of energy can be used to illustrate the loss of usable energy at each feeding level

·        Only 10% of ingested nutrients are used to synthesize new tissues…remaining energy is used for life functions

PYRAMID OF BIOMASS

·        The decrease in available energy at each higher feeding level means less organic matter, or biomass, can be supported at each higher level.

·        Thus, the total mass of producers in an ecosystem is greater than the total mass of primary consumers. Primary consumer greater than secondary consumers

·        A pyramid of biomass illustrates the decrease in biomass at each higher feeding level.

·        gross primary production- total primary production…the amount of light energy that is converted to chemical energy by photosynthesis per unit of time

·        net primary production- is equal to the gross primary production minus the energy used by the primary producers for respiration

§         Represents the storage of chemical energy that will be available to consumers in an ecosystem.

§         Referred to as biomass

 

Symbiotic relationships: organisms that live together in a close association; may or may not be beneficial to the organisms involved

Commensalism; one organism benefits and the other is not adversely affected ex. Barnacles living on a whale, orchids living in a tree

Mutualism; both organisms benefit ex. Aphids and ants, protozoans living in the digestive tract of termites; Lichen; made up of algae and a fungus…fungus provides moisture, minerals and anchor…algae; photosynthetic, provides food…another example...Nitrogen-fixing bacteria living in the roots of legumes (bacteria provides nitrogen compounds and the plant provides nutrients and good environment

Parasitism; one organism (parasite) benefits and the other (host) is harmed. Examples athlete’s foot fungus…tapeworms. Heartworms

·        Parasite and host

·        endoparasitic- parasites that live within a host…tapeworm

·        ectoparasitic- parasites that feed off external tissue of the host…mosquito, warts, aphids

·        parasitoidism- lay eggs on living host…wasps

 

Predation- feeding off of other living things

§         herbivory …herbivore feeding on part of a plant

§         parasitism

·        Predator Adaptations

§         Agility, fangs, claws, heat-sensing organs as in the viper snake.

·        Plant defenses

·        Animal defenses against predators

§         Monarch and Viceroy butterflies

§         Mimicry

§         Camouflage 

Ecological formation;

 Ecological Succession: the replacement of one kind of community by another in an ecosystem

Pioneer Organisms: the first to appear

Primary Succession: when life forms appear in place where life had not existed before.

Secondary Succession: succession that occurs when a habitat has been disturbed (soil left intact).

Biome: a major terrestrial community: described in terms of the dominant kind of vegetation found there

Biome	Characteristics	Plants (flora)	Animals (fauna)
Tundra tundra pic 1 tundra pic 2	Permanently frozen subsoil	Lichens, mosses, grasses	Snowy owl, caribou, polar bear
Taiga Taiga 1 Taiga 2	Long, severe winters; summers with thawing subsoil	Conifers	Moose, black bear, Reindeer
Temperate Deciduous Forest deciduous 1	Moderate precipitation, cold winters, warm summers	Deciduous trees, grasses…go outside	Gray squirrel, fox, deer
Tropical rainforest Tropical Rainforest 1	Heavy rainfall; constant warmth	Many species of broad-leaved plants	Snake, monkey, leopard
Grassland grassland1	Considerable variability in rainfall and temperature; strong prevailing winds	Grasses	Prairie dogs, bison
Desert desert 1	Sparse rainfall; extreme daily temperature fluctuations	Drought- resistant shrubs and succulent plants	Lizard, kangaroo rat
Savanna Savanna 1	Grassland with scattered individual trees; soils low in nutrients;	Grasses, small broad leaf plants	Zebra, giraffe

 

Population ecology

Geographical Range: A population’s geographical range is the geographic limits within which it lives.

·        Within the range, local densities may vary substantially because not all areas provide equally suitable habitat, and because individuals exhibit patterns of spacing in relation to other member of the population

Patterns of Dispersion

Patterns of Dispersion 1, Patterns of Dispersion 2, Patterns of Dispersion 3

Clumped: individuals are aggregated (clumped) in patches ex. School of fish

·        Schooling increases efficiency of swimming, reduce predation risks and increase feeding efficiency

Uniform; spacing is even; ex king penguins

Random; spacing varies in an unpredictable way; trees of same species are often randomly distributed in forests (this pattern of dispersion is rare)

 

Survivorship curves

Survivorship is an important factor in the changes in population size over time

SURVIVORSHIP CURVES; a graphic way of representing some of the data in a life table… a graph showing the proportion or numbers of a cohort still alive at each age.

Cohort- a group of individuals of the same gage, from birth until all are dead.

 

3 general types of curves

Type I; (humans) high survival rates until old age

Type II (hydra) a constant proportion of individuals die at each age

Type III; (oyster) experience very high mortality as larvae but decreased mortality later in life.

 

Age Structure: relative number of individuals of each age. Only annual plants and insects, in which adults all reproduce at about the same time and then die, do not have overlapping generations. 

·        Important in determining the rate at which a population is growing

·        Zero population growth

 

Sex ratio; proportion of individuals of each sex

·        The number of females is usually directly related to the number of births than can be expected, but the number of males may be less significant because in many species, a single male can mate with several females.

 

Population Growth

Demography- the statistical study of populations

3 Key features used to predict how a population will grow

1. Population Size- very small populations are most likely to become extinct. Inbreeding produces a more genetically uniform population in which recessive traits, many unfavorable, are more likely to be expressed.

2. population density- the number of individuals found in a given area, If the individuals of a population are widely spaced, they may rarely, if ever, encounter one another

3. Dispersion- the way in which the individuals of the population are arranged…clumped, random, or uniform

 

Exponential Growth

• Growth that occurs when a population is in an ideal environment
• Growth is unrestricted; plenty of resources, space, no disease, no predators
• Exponential increase results in a J-shaped curve
• Growth occurs very quickly ex. Insects and bacteria
• As population increase individuals compete with each other for resources
• Population reaches carrying capacity and the curve levels off

Logistic Growth

• Population size is restricted in size because of limited resources
• S-Shaped Curve

Stages of logistic growth curve

1. the initial establishment of the population with a slow growth rate
2. exponential growth curve
3. stabilization around the carrying capacity

 

Stage 1

• r (rate of growth)= birth rate – death rate
• r can be expressed as 0, +, -

 

Stage 2

• used to calculate the number of individuals that will be added to the population as it grows
• ∆ (DELTA) N=rN
  • r = rate of increase (birth rate-death rate)
  • N= the size of the current population
  • When population size is plotted against time this model produces exponential growth curve
  • Rate of increase remains constant, but the amount by which the population grows rises quickly as the size of the population increases (J-Shaped curve)
  • No population exhibits exponential growth for very long, they begin to run out of resources and accumulated waste. Eventually growth will stabilize to fit with what the environment can hold
  • Carrying Capacity- the population size that an environment can sustain
    • A single bacteria cell that dived every 30 minutes…there would be over a million bacteria after only 10 hrs….within a year a single bacterium would reproduce enough offspring to cover the Earth….1 Km thick
    • Example: Ideal conditions. all the food, water shelter is provided; no competition.
    • Biotic potential: maximum rate of increase per individuals under ideal conditions.
    • If house cats that have not been neutered or spayed live up to their BIOTIC POTENTIAL, two can be the start of many kittens.

• 12 the first year
• 72 the 2^nd
• 429 3^rd
• 2574 4^th
• 15416 5^th
• 92332 the 6^th
• 553,019 the 7^th
• 3,312,280 the 8^th
• 19,838,741 kittens the 9^th yr

Stage 3 Stabilization around the carrying capacity

• adjustments to compensate for diminishing resources
• because this stage accounts for the declining resources available to populations (as they grow) it is called LOGISTIC MODEL of a population growth
• Competition for food, shelter, mating sites and other resources as well the accumulation of toxic wastes increases as a population approached carrying capacity

 

As resources decreases

• Individuals begin to compete…not enough resources to go around
• Death rate increases
• Birth rate decreases
• Growth of population slows
• Zero population growth (death rate=birth rate)
• Human population can quickly grow past the environment’s ability to support it
• Famine and disease
• As populations grow resources become scarce (food and living space)
• Organisms produce more offspring that survive
• The carrying capacity (limited resources) prevent an explosion of a population

 

Limiting Factors: forces that slow the growth in population- elements that prevent a population from attaining its biotic potential (maximum growth rate)

Density-dependent factors- created by increase of population and limited resources

Density-Independent factors- natural disasters, earthquakes, extremes of climate

 

 

Formula for Logistic Population Growth

∆N= rN [(K-N)/K]

∆N= number of individuals added to the population

• Gains and losses in Population size
  • Gains:
    • Birth
    • Immigration: the arrival of new residents from other population of the species.

 

• Losses
  • Death
  • Emigration: individuals move out of a population.

 

r= rate of growth

N= the size of the current population

K=carrying capacity (the maximum stable population size that a particular environment can support over a relatively long period of time)

Carrying Capacity of a cockroach

Exponential Growth vs Logistic growth

 

 

2 Strategies of Population Growth

r-strategists

• Characterized by exponential growth which results in temporarily large populations followed by sudden crashes in population size
• Species tend to live in unpredictable and rapidly changing environments... places where it pays to be able to reproduce quickly when conditions are favorable
• Main purpose is to reproduce quickly, in high numbers and reproduce early in life
• Ex. Weeds, dandelions, bacteria and insects

K-strategists

• Characterized by a high degree of specialization
• Tend to live in environments that are stable and predictable…where it pays to be able to compete effectively
• Tend to reproduce late in life and have few offspring
• Offspring are large
• Tend to become large animals
• Long life span
• Fewer competitors
• Smaller populations
• Young receive parental care

	R-strategists	K-strategists
Growth Pattern	Exponential	Slow
Population Size	Temporarily large	Small
Environment	Unpredictable	Stable
Reproductive Strategy	Early in life, when conditions are favorable	Late in life, under most conditions
Characteristics of offspring	Many in number, small in size, mature rapidly, little or no parental care	Few in number, large in size, mature slowly, receive parental care

 

Niche- the role an organisms plays in the environment

Ecological Niche; the sum total of the organism’s use of the biotic and abiotic resources in its environment

Fundamental niche; refers to the set of resources a population is theoretically capable of using under ideal circumstances

Realized niche; the resources a population actually uses

Fundamental vs realized niche

Species richness; the number of species within a community

Relative abundance; the population size of each species in a community. Ecologist recognize that some communities consist of a few common species and many rare ones, whereas others contains an equivalent number of species that are all about equally common

Species Diversity; considers both components of diversity: species richness and relative abundance

Stability is the tendency of a community to reach and maintain an equilibrium or relatively constant condition

 

Chemical Cycles: Death and recycling

Biogeochemical cycles are closed cycles…nonliving enters living…then back to environment

Water Cycle

 

 

Carbon Cycle

3 ways carbon is cycled

1. Cellular respiration

2. combustion

3. erosion

 

Nitrogen Cycle  (Nitrogen Cycle 2)

4 important states

1. Assimilation

• Absorption and incorporation of nitrogen into plants and animal compounds
• Ammonia spreads through the soil, picked up by plants to build proteins, nucleic acids and other nitrogen containing molecules. Animals eat plants

2. Ammonification

• Production of ammonia by bacteria during the decay of nitrogen containing organic matter
• Animals excrete nitrogen in urine as urea or uric acid

3. Nitrification

• The production of nitrate from ammonia
• Some of the ammonia in the soil is converted by several kinds of bacteria to nitrate (NO₃)

4. Denitrification

·        Another kind of bacterium acts on the remaining nitrate, converting it back into nitrogen gas. The gas is released into atmosphere completing the cycle

Phosphorus Cycle

Essential element for all living organisms: key part of DNA and ATP

·        Present in soil and rocks (calcium phosphate) which dissolves in water to form phosphate ions

·        Absorbed by plants

·        Animals eat plants

·        When they doe, bacteria in soil convert the phosphorus in organic molecule back into phosphate ions

·        Phosphorus levels in freshwater lake ecosystem in often low, which prevents growth of photosynthetic algae. Added phosphorus (detergents and fertilizers) cause an increase algal growth or bloom. Bacteria feed on dead algae using dissolved oxygen. This decrease in oxygen levels kills fish and other invertebrate animals (suffocate/drown)