Chapter 36: Population Growth. Population Concepts. Population: Carrying Capacity: Critical Number: Growth Rate: Growth rate = Birth rate - Death rate

Transcription

1 Chapter 36: Population Growth Population: Population Concepts interbreeding group of same species Carrying Capacity: maximum population size an ecosystem can sustainably support Critical Number: minimum population size required for its survival Growth Rate: change in population size per unit time e.g. 10% increase per year accounts for births and deaths Growth rate = Birth rate - Death rate e.g. 10% = 15% - 5% A population is stable, at equilibrium if: Birth rate = Death rate (immigration, emigration also affect population size) 1

2 Population Growth Patterns Unchecked population growth will be exponential population increase by the same factor over time (e.g., doubling per generation) can result in a population explosion Exponential growth will eventually resolve into one of 2 basic growth patterns J-curve Carrying Capacity S-curve (@ equilibrium) J-curve Growth Occurs when populations undergo exponential growth beyond carrying capacity followed by a crash 2

3 S-curve Growth S-curve growth (aka logistic ) population level hovers around carrying capacity due to environmental resistance typical of established species in stable ecosystems J-curve growth exponential growth beyond carrying capacity followed by crash associated w/ introduced species, loss of predator, habitats that fluctuate may be temporary & resolve to S-curve over time Environmental Resistance All factors (biotic & abiotic) that limit or resist population increase Density-dependent factors: environmental resistance factors that change in response to population density usually biotic (predators, disease, food supply) provide more resistance as population expands, less as it shrinks (keeps pop. at carrying capacity) Density-independent factors: resistance that is unrelated to population density usually abiotic (changes in weather, fire, ) 3

4 Predator/Prey Population Cycles Predators provide a form of density-dependent environmental resistance: predator numbers increase/decrease in response to prey populations 160 Snowshoe hare Hare population size (thousands) Lynx Lynx population size (thousands) keeps prey populations in check Year Key Terms for Chapter 36 population, growth rate carrying capacity, critical number J-curve, S-curve growth environmental resistance Chapter 37: Communities & Ecosystems 1. Biological Communities 2. Energy Flow in Ecosystems 3. The Cycling of Matter 4

5 1. Biological Communities Communities and Niches Community: all interacting, living organisms in a given region consists of many different & diverse species, each with a unique niche or role Niche: sum of a species use of resources food, living space, environmental requirements unique for each species, but can overlap between species How do Species Interact? 5

6 Competition Intraspecific: within same species most common type of competition members of same species share same niche important part of natural selection Interspecific: between different species less common since different species tend to have different niches occurs between species with overlapping niches e.g., plants competing for space, sunlight & water Competitive Exclusion If 2 different species occupy same niche, one will outcompete and eliminate the other evolution selects for species with unique niches Predator & Prey All species that don t produce their own food (e.g., photosynthesis) or feed on dead, waste material (detritus feeders) prey on other organisms: 3 basic Predator Preyrelationships: *Carnivore Herbivore Herbivore Producer (plant) Parasite Host 6

7 Predators have an Important Role Keep other species in balance, their removal can lead to overgrowth of prey, severely disturbing ecosystem balance. Species with essential roles for ecosystem balance are called keystone species: usually predators that prevent domination of the ecosystem by one species e.g. starfish control mussel populations otters & lobsters control urchin populations wolves control deer populations Symbiotic Relationships Symbiosis: a close, prolonged association between two species Mutualism (both species benefit) e.g., plants & insects; coral & algae many species depend on such relationships for survival Commensalism (one benefits, other unharmed) e.g., barnacles on a whale, epiphytes Parasitism (one benefits, one is harmed) e.g., mistletoe, tapeworms host usually survives 2. Energy Flow in Ecosystems 7

8 What is an Ecosystem? a distinct biological community and its abiotic environment biotic = living or derived from living things living organisms and their products, remains abiotic = unrelated to living things non-living matter (water, air, minerals ) ecosystems are functional units of sustainable life Examples of Ecosystems ecosystems are defined by their plant life biomass varies greatly among ecosystems biomass = dry weight of living material Energy and Matter in Ecosystems Energy constantly flows through ecosystems solar energy is the ultimate source (usually) converted to chemical PE via photosynthesis passes through the food web, gradually being dissipated as heat Matter is recycled within ecosystems organic material is continually built and broken down using the same elements (requires energy!) **Earth continually gains and loses energy, while matter is essentially confined to the planet** 8

9 Energy flows in/out, Matter is recycled Energy flow Chemical cycling Light energy Chemical energy Heat energy Chemical elements Energy is Transferred by Feeding There are 3 major trophic (feeding) categories: 1) Producers (autotrophs) convert energy of sunlight to food energy by photosynthesis 2) Consumers require food produced by other living organisms feed on producers, or each other herbivores, carnivores, omnivores 3) Detritus Feeders feed on nonliving organic matter dead organisms, organic waste include the decomposers (mostly bacteria & fungi) break down organic material completely very important for recycling nutrients **Without detritus feeders, ecosystems would collapse!** 9

10 Trophic Relationships Trophic levels of the Food Chain : 1 st trophic level = producers photosynthesizers (plants, phytoplankton) 2 nd trophic level = herbivores primary eat producers 3 rd trophic level = carnivores secondary eat herbivores 4 th trophic level = bigger carnivores tertiary eat carnivores **There is also a detritus food chain ** Trophic level Quaternary conusumers Hawk Killer whale Terrestrial food chain Snake Mouse Grasshopper Tertiary Secondary Primary Tuna Herring Zooplankton Aquatic food chain Producers Plant Phytoplankton Energy Transfer is Inefficient Tertiary Secondary Primary 1,000 kcal 10 kcal 100 kcal ~10% of food energy is transferred to each successive trophic level! Producers 10,000 kcal 1,000,000 kcal of sunlight 10

11 Where does this Food Energy go? Most is lost as heat due to respiration used to meet the energy needs of the organism Some is not consumed not all potential food is eaten Not everything is digested digestion is usually incomplete, and some material is indigestible (fiber, etc) Only ~10% is incorporated into organic molecules i.e., potential food for other organisms thus biomass decreases by ~90% at each trophic level Trophic level Energy & Human Food Production Secondary Human meat-eaters Primary Human vegetarians Cattle Producers Corn Corn Due to inefficient food energy transfer, animal-based food production is much less efficient and more expensive than plant-based food production. 3. The Cycling of Matter 11

12 All matter in Ecosystems is Recycled We will focus on the cycling of 3 key elemental nutrients between abiotic reservoirs and organic material: Carbon Nitrogen Phosphorus The Carbon Cycle CO 2 in atmosphere Photosynthesis Cellular respiration the cycling of carbon between CO 2 & organic molecules Burning of fossil fuels and wood Carbon compounds in water Higher-level Primary Detritus Decomposition Summary of the Carbon Cycle Carbon from CO 2 in the atmosphere or water is fixed into organic molecules by photosynthesis. this is how carbon enters the food web Carbon in organic molecules eventually returns to atmosphere (or water) in molecules of CO 2 due to: respiration fires volcanic activity burning of fossil fuels* ***Increased CO 2 due to fossil fuel burning results in global warming and lowering of ocean ph*** 12

13 Nitrogen in atmosphere (N 2 ) The Nitrogen Cycle Nitrogen Assimilation fixation by plants Denitrifying Nitrates bacteria Nitrogen-fixing (NO bacteria in root 3 ) Detritivores nodules of legumes Decomposition Nitrifying bacteria Ammonium (NH 4+ ) Nitrogen-fixing soil bacteria the cycling of nitrogen between N 2, inorganic ammonium & nitrate ions & organic molecules Summary of the Nitrogen Cycle Nitrogen fixation is one of the most important processes on earth! converts nitrogen compounds in the atmosphere (mainly N 2 ) to ammonium ions (NH 4+ ) nitrifying bacteria convert NH 4+ to nitrate (NO 3- ), the most easily assimilated form of nitrogen for plants plants cannot use atmospheric nitrogen (N 2 ) directly nitrogen thus enters the food web through plants Atmospheric nitrogen is fixed by: cyanobacteria (blue-green algae) in water various soil bacteria and fungi on land more on the Nitrogen Cycle Denitrification is a microbial process that produces N 2 from nitrates returns nitrogen to the atmosphere, completes the cycle Most nitrogen actually cycles between plants,, & detritus feeders which metabolize organic nitrogen compounds back to NH 4 + **Human activity (synthetic fertilizers, fuel burning) results in excess fixed nitrogen entering ecosystems** 13

14 The Phosphorus Cycle the cycling of phosphorus between inorganic phosphate & organic molecules Weathering of rocks Geologic uplift of rocks Sedimentation Runoff Soil Rain Plant uptake of PO 4 3 Plants Consumption Leaching Decomposition Summary of the Phosphorus Cycle Phosphorus originates as inorganic phosphate (PO 4 3- ) in rocks, leaches into soil & water, and is incorporated into organic compounds by plants Decomposition of dead tissue & animal wastes release inorganic phosphate back into soil to re-enter the food web via plants. **Agricultural runoff (synthetic fertilizer, animal waste), untreated sewage release an excess of phosphorus (& nitrogen) into ecosystems, causing imbalance** due to overgrowth of algae, bacteria & certain plants Key Terms for Chapter 37 ecosystem, community, niche competition, predation, keystone species symbiosis: mutualism, commensalism, parasitism producer, consumer, autotroph, heterotroph herbivore, carnivore, omnivore, detritus feeder trophic levels, food web, biomass Relevant Review Questions: 1-3, 5, 7, 8, 10, 11, 13 14