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NSCI 1413 (15)
Lecture 2

NSCI 1413 Lecture 2: Ecology

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Natural Science
NSCI 1413
Guy Robinson

Important Vocabulary ● Population:​ A group of individuals of one species living in one area who have the ability of interbreeding and interacting w/ each other ● Community:​ Consists of all the organisms living in one area ● Ecosystem:​ Includes all the organisms in a given area as well as the abiotic factors w/ which they interact ● Abiotic factors:​ Nonliving things that include temperature, water, sunlight, wind, rocks, and soil ● Biosphere:​ The global ecosystem Properties of Populations ● Size:​ The total number of individuals in a population; represented by N ● Density:​ The number of individuals per unit area or volume ○ Mark and Recapture:​ A sampling technique where organisms are captured, tagged, and then released; later, the same process is repeated and the following formula is used for the collected data N = ​(# of marked in first catch)(total # in second catch) # of recaptures in second catch ● 50 zebra mussels are captured, tagged, and released; one week later, 100 zebra mussels are captured and 10 have markings already; using the formula, the total population would be ~500 zebra mussels ● Dispersion:​ The spacing patterns of individuals w/i the area the population inhabits ○ Clumped:​ Mechanism used for survival under the pretence of “safety in numbers” ● Fish traveling in schools ○ Uniform:​ Evenly spread out, usually to prevent one individual from “hogging” resources ● Certain plants secrete toxins that keep away plants who would compete for limited resources ○ Random:​ Occurs in the absence of any special attractions or repulsions ● Tree placement in forests is random ● Survivorship/Mortality Curves:​ Show the size and composition of a population ○ Type 1:​ Shows organisms in low death rates in you and middle age and high mortality in old age; great deal of parenting accounts for the high survival rate of young (ex: humans) ○ Type 2:​ A species w/ a death rate that is constant over the life span (ex: hydra, reptiles, rodents) ○ Type 3:​ Shows a very high death rate among young but mortality rates decline for individuals who have survived past a certain age; characteristic of no parenting (ex: fish) ● Age Structure Diagrams:​ Shows the relative numbers of individuals at each age Population Growth ● Biotic Potential:​ The maximum rate at which a population could increase under ideal conditions; contributing factors include: ○ Age reproduction begins ○ Life span during which organisms are capable of reproducing ○ The number of reproductive periods in a life time ○ The number of offspring the organsism is capable of reproducing ● Carrying Capacity:​ The limit to the number of individuals that can occupy one area at a particular time ● Limiting Factors:​ Factors that limit population growth ○ Density-dependent:​ Factors that ↑ directly as the population density ↑; includes competition for food, buildup of wastes, predation, and disease ○ Density-independent:​ Factors whose occurrence is unrelated to population density; includes natural disasters ● Growth Patterns ○ Opportunistic:​ Species reproduce rapidly when the environment is uncrowded and resources are vast; aka r-strategists ○ K-strategists:​ Live at density near carrying capacity (K) Comparison of Two Life Strategies r-strategists K-strategists Many young Few young Little or no parenting Intensive parenting Rapid maturation Slow maturation Small young Large young Reproduce once Reproduce many times Example: Insects Example: Mammals ● Case Study of The Hare and The Lynx ● Hares eat grass, lynx eat hares; studied population fluctuation using pelt data from hunters ● Lynx population dependent on the hare population as a food source, and change accordingly Community Structure and Population Interactions ● Competition ● Competitive Exclusion Principle:​ Developed by G. F. Gause; cultured two similar species separately, and grew rapidly then leveled out at carrying capacity, but when cultured together, one had the advantage and drove the other to extinction; two species cannot coexist in a community if they share a niche and use the same resources; two outcomes: ● Resource Partitioning:​ One species evolves through natural selection to exploit different resources ● Extinction​ of one species ● Predation:​ Refers to one animal eating another or animals eating plants; defenses have been developed: ● Plants:​ Evolved spines, thorns, and chemical poisons (strychnine, mescaline, morphine, nicotine) to fend off animal attacks ● Animals:​ Evolved active defenses (hiding, fleeing, defending) that be costly in terms of energy; also evolved passive defenses such as: ● Aposematic coloration:​ Very bright coloring indicating poisonous animals as a warning that predators should avoid them ● Batesian mimicry:​ “Copycat coloration”; one harmless animal mimics the coloration of one that is poisonous ● Viceroy butterfly:​ Mimics the monarch butterfly that stores milkweed poison in its body ● Müllerian mimicry:​ Two or more poisonous species resemble each other and gain an advantage in their combined numbers; predators learn quickly to avoid any prey w/ that appearance ● Wasps and Bees ● Mutualism:​ A symbiotic relationship where both organisms benefit (+/+) ● Bacteria in the human intestine that produce vitamins ● Commensalism:​ A symbiotic relationship where one organism benefits while the other is unaware of the other organism or the other is not harmed by the one organism, (+/o) ● Barnacles attach to the underside of whale, gaining access to a variety of food source; doesn’t help or harm the whale ● Parasitism:​ A symbiotic relationship where one organism, the parasite, benefits while the host Is harmed (+/-) ● Tapeworm inside a human Energy Flow and Primary Production ● The sun provides all the sunlight energy to the supply the needs of all living organisms, despite the fact that only less than 1% is actually converted into useable energy via photosynthesis, while the rest is reflected, absorbed as heat, or radiated ● Gross Primary Productivity:​ The amount of light energy that is converted to chemical energy by photosynthesis per unit of time ● Net Primary Productivity:​ Number equal to the GPP minus the energy used by producers for their own cellular respiration ● Tropical rain forests are among the most productive terrestrial ecosystems, providing a large portion of Earth’s overall NPP ● Coral reefs have a very high NPP, but since they occupy a small fraction of the planet, they provide very little to the global NPP Energy Flow and the Food Chain ● Food Chain:​ Pathway along which food is transferred from one trophic level to another ● Biomass:​ Organic material from living, or recently living organisms that serve as fuel ● Only ~10% of the energy stored in any trophic level is converted to organic matter at the next trophic level​ (why trophic levels are so short, only containing a handful of organisms at most) ● Start w/ 1,000g of plant matter, the food chain can only support 100g of herbivores, 10g of secondary consumers, and 1g of tertiary consumers (reduced by factors of 10) ● Population fluctuations at lover trophic levels are magnified at higher levels​ (why short food chains are more stable—endangerment or extinction of lower organisms can lead to the same in higher level consumers) ● Food chains are not isolated​; they are interwoven w/ other food chains into a ​food web​, meaning one organism can occupy a high trophic level in one food chain and a low trophic level in another ○ Producer:​ Convert light energy to chemical bond energy; greatest biomass of any trophic level; autotrophs; bottom of the food chain; most stable trophic level; population fluctuations have no significant effect ● Grass ○ Primary Consumer:​ Heterotrophs; herbivores (eat producers) ● Grasshopper ○ Secondary Consumer:​ Heterotrophs; carnivores (eat primary consumers) ● Mouse ○ Tertiary Consumer:​ Heterotrophs; carnivores (eat secondary consumers); top of the food chain; have the least biomass; least stable trophic level; very sensitive to population fluctuation ● Hawk ● Biological Magnification:​ A phenomenon where organisms at higher trophic levels have greater concentrations of accumulated toxins stored in their bodies than those at lower trophic levels ● Bald Eagle:​ Nearly became extinct in the 1950s due to the pesticide DDT that entered the food chain at the primary consumer level, accumulating at the top in eagles (DDT interferes w/ deposition of calcium in eggshells, so eagle eggs broke easily and few eaglets hatched) ● Decomposers:​ Bacteria and fungi; recycle nutrients back to the soil; critical to the food chain (or else it would collapse) Ecological Succession ● Rebuilding of an ecosystem; the order in which mature ecosystems come to be after major disasters or new colonization of species ● Primary ecological succession:​ When rebuilding begins in a lifeless area where even soil has been removed; characterized by soil building; drived by weathering and organic matter accumulation; very slow and gradual ○ Pioneer organisms:​ The first organism to inhabit a barren area (ex: mosses and lichens); introduced with wind as a vector in spore form ● Once soil is present, pioneer organisms are overrun by larger ​organisms (grasses, bushes, then trees) ● Climax community:​ The final, stable community left as a result of complete ecological succession ● Secondary ecological succession:​ When an existing community has been cleared by some disturbance that leaves soil intact (ex: fires in Yellow Stone Nation Park, 1988) Biomes ● A major biotic community characterized by the dominant forms of plant life and the prevailing climate ● Trend in northerly climates:​ tropical rainforest → desert → grass land → deciduous forest → taiga → tundra ● Trend in mountain ranges (as elevation ↑, and humidity/temp ↓):​ temperate deciduous forest → taiga → tundra ● Marine: ○ Largest biome, covering ¾ of the earth’s surface ○ The most stable biome w/ temperatures that vary little b/c water has a high heat capacity and since volume of water is enormous ○ Provides most of the earth’s food and oxygen ○ Divided into regions classified by the amount of sunlight they receive, distance from the shore, water depth, and whether it is open water or ocean
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