Ch18,19_Ecology, populations & human

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1 Basic Ecological Concepts What is ecology? A branch of biology that involves The study of the relationships between organisms and their environment Biotic factors: living part of the ecosystem, all the organisms living there Abiotic factors: non-living part of the ecosystem, all the physical and chemical factors like temperature, ph, light, etc. 1

2 Population Ecology Deals with populations, which are groups of individuals of the same species living in the same area Concentrates mainly on factors that affect a population s Size Population density Growth Structure Examples of population ecology How to develop sustainable fisheries Increase populations of organisms we wish to harvest How to control pests and pathogens Save populations of organisms threatened with extinction Human population growth Review: How populations grow: Modes of reproduction Only 1 parent Individual can grow isolated and still reproduce No genetic variability New individuals are clones of the parent Good mutations are passed more efficiently in clones No energy is used in finding a mate boring! Useful when the individual is well adapted to the environment Asexual Gen.1 Gen.2 Gen.3 Gen.4 Asexual Sexual Sexual 2 parents needed Genetic variability ensured by meiosis & sexual reproduction New individuals are not equal to parents Less offspring in the same time 2

3 Example: Dinoflagellates Occasionally they undergo dramatic population explosions by asexual reproduction Blooms Some of them related to red tides Red tide But the population does not grow forever why? Many factors affect the way populations growth Reproductive capacity or Biotic potential Theoretical maximum rate of reproduction Generally, several times larger than the number of offspring needed to maintain the population I) High reproductive capacity without caring for the young Low survival rate of young 2 possible strategies II) Low reproductive capacity with parental care and protection of the young High survival rate of young Energy is used more in reproduction Energy is used more in parental care Invertebrates Amphibians, Fish, Reptiles Birds Mammals Some Fish 3

4 Population size Population size limitations : Limiting factors Any factor that prevents a population from growing any larger Carrying capacity Maximum number of individuals that the environment can sustain in a given area is reached when birth rate balances with death rate Availability of raw materials and energy Production and disposal of waste Interactions with other organisms Competition Predators Diseases Limited space Time Density Dependent limiting factors As population size increases Competition increases The growth rate declines in proportion to the intensity of competition A density-dependent factor is a population-limiting factor whose effects intensify as the population increases in density. Decreasing birth rate Density Independent limiting factors Are limiting factors whose intensity is unrelated to population density Include abiotic factors such as Fires Floods Storms Chance events limiting factors! Decreasing survival rate 4

5 The population growth curve Describes the change in population size over time considering both reproductive capacity and environmental pressure (limiting factors) Stable Phase IN factors are in a sort of equilibrium with OUT factors IN OUT Natality: N/1000 Mortality: N/1000 Emigration Immigration Predation Competition Parasitism Diseases Exponential Phase IN factors always exceeds OUT Lag Phase High natality and high mortality Plenty of resources Age distribution Distribution of individuals among age groups. Allows to see The history of a population s survival Reproductive success How the population relates to environmental factors Natural populations Postreproductive Reproductive Prereproductive 5

6 Life Tables Track survivorship: chances of survival in an individual to various ages Help to determine the most vulnerable stages of the life cycle In humans, the most vulnerable stages are above 80 years old Sex ratio Pair-bonding species Number of males compared to females 1 : 1 1 : N Elks Lions with 1 < N Less males does not necessarily mean decline in the population! Population density Number of individuals per unit of area Density-dependent factors may include Accumulation of toxic wastes Limited food supply Limited territory Competition Parasites 6

7 Billions of people Human Population growth Is still considered to be in the exponential phase! Why? 1) Agricultural and Industrial Revolutions (19 th centuries) 2) Introduction of compulsory vaccination and improvements in medicine and sanitation (19th century) 3) Scientific and Technological advances (20th century) Old stone age Beginning of agriculture, domesticatio n of animals and plants New stone age Bronze age Iron age Almost 5 billion in a lifetime! Middle ages ,000,000, ,000,000, Modern times B.C. A.D. Health & Disease Control Farming Practices Genetically Modified Organisms Pests control Global scale fisheries Food transportation Mortality rates have dropped considerably. More people survive now then ever before! Human Population: Related questions 1) How much population can the Earth sustain? 2) How much are we affecting the ecosystem? 3) Do biological and technological advances influence populations of the world at the same level? 4) Do we count with the necessary technology as to understand how things work in our planet and control the human population growth? 300 THOMAS MALTHUS 1798 An Essay on the Principle of Population Human growth: geometric: 2,4,8,16,32 Supply of food: arithmetically: 1,2,3,4,5 population must inevitably outgrow the available supply of food Food Humans Time 7

8 Main impacts of humans on the environment Habitat Destruction or Fragmentation (Deforestation, Farming practices, Agriculture) Overfishing (Overexploitation) Pollution Usually better competitors, they do well in disturbed Invasive Species environments, and displace native species (Also called Introduced, Exotic, or Non-native) Global warming and climate change Decrease of the ozone layer Chemical cocktails effects on organisms 8

9 Pesticides & other Persistent Organic Pollutants (POPs) Substances that circulate in the environment for years Chlorinated hydrocarbon pesticides DDT Biomagnification Increase in a concentration of a substance as it moves up in a food chain Pesticides accumulate at higher trophic levels Marine birds (brown pelican) DDT interfieres with calcium deposition Eggshells become thin They brake during incubation The Loss of Biological Diversity (Biodiversity) Does it really matter? It is estimated that the average annual value of ecosystem services each year in the United States is more than $33 trillion! Biodiversity loss means losing Genetic diversity Species diversity Ecosystem diversity Healthy ecosystems do a lot of beneficial things! Purify air and water Decompose wastes Recycle nutrients 9