Ecology: Part III Populations - Species Interactions and Growth

Ecology Part III: Populations Learning objectives Explore some more ecology basics with regard to species Delve into populations of species and what affects population growth Ecology: Part I, Species Ecology: Part I, Species Species - organisms of the same kind that are genetically si...

Ecology Part III: Populations Learning objectives Explore some more ecology basics with regard to species Delve into populations of species and what affects population growth Ecology: Part I, Species Ecology: Part I, Species Species - organisms of the same kind that are genetically similar enough to breed in nature and produce live, fertile offspring Species interactions Population - all the members of a species living in a given area at the same time Biological Community - all of the populations living and interacting in a particular area Ecosystem - biological community and its physical environment Ecology: Part I, Species What is a species? Species - organisms of the same kind that are genetically similar enough to breed in nature and produce live, fertile offspring Ecology: Part I, Species What makes a species? What makes a species? Adaptation Evolution Why do some species live in one place but not another? Adaptation - the acquisition of traits that allow a species to survive in its environment Adaptation can occur at the individual level and the population level. When it occurs at the population level this can lead to evolution of a species https://www.youtube.com/watch?v=mZt1Gn0R22Q What makes a species: Evolution Individuals with inherited (genetic) traits that make them suited to a particular environment survive and reproduce at a greater rate in that environment than individuals with less suitable traits. Evolution can occur via multiple mechanisms. Natural selection is on of those mechanisms. Others include mutation, gene flow, genetic drift  What makes a species: Evolution through Natural Selection The process of better-selected individuals passing their traits to the next generation is called natural selection. Where do the differences in the genes within individuals come from? Mutations - changes in DNA coding sequence that occur by chance (e.g., random mistakes in DNA replication, exposure to radiation, toxins...) How do new species occur? Speciation Speciation - the development of a new species. This can occur due to geographic isolation or other means (e.g. behavioral isolation) whereby a sub-population becomes separated from the main population and can no longer share genes with it. Speciation The new population evolves independently of the first, creating a new species. This is termed allopatric speciation. Speciation In sympatric speciation, organisms continue to live in the same place but become isolated by some other means. https://www.youtube.com/watch?v=udZUaNKX bJA *Stop at 3:20 BOB Activity with sticky notes Ecology: Part I, Species Species interactions.  The Forms of Species Interactions A. No effect of interaction (0/0) B. Consumer / Prey (host) (+/-) + B E D species 1 Effect on C. Interspecific competition (-/-) F A E 0 D. Mutualism (+/+) - C F B E. Commensalism (+/0) - 0 + Effect on F. Amensalism (-/0) species 2 Slide courtesy of Dr. Rebecca Irwin Species Interactions: When one limiting resource is involved Competition Intraspecific competition (-/-) - competition among members of the same species How might humans participate in this? Interspecific competition (-/-) - competition between members of different species Interspecific competition can lead to competitive exclusion….  Competition Ecological Niche Ecological niche- the total set of environmental factors that determine a species distribution in space and time INVASIVE SPECIES Competitive exclusion (competition)- no two species can occupy the same ecological niche (MacArthur); if two species compete for the same resource (interspecific competition); it is possible that one species will be more efficient in using the resource and outcompete the other Resource https://www.youtube.com/watch?v=QnYaoKamXQw partitioning - species co-exist in a habitat by utilizing different parts of a single resource. Ecology: Part II, Populations Ecology: Part I, Species Species - organisms of the same kind that are genetically similar enough to breed in nature and produce live, fertile offspring Species interactions Population - all the members of a species living in a given area at the same time Biological Community - all of the populations living and interacting in a particular area Ecosystem - biological community and its physical environment Ecology: Part II, Populations How do populations of species grow? Describing Population Growth Mathematically (N) Population – total number of all the members of a single species living in a specific area at the same time. (r) Rate - This is the rate of growth; the number of individuals which can be produced per unit of time under ideal conditions (with no limits to the population’s growth). (t) Time - This is the unit of time upon which the rate is based. Geometric Rate of Increase--The population size that would occur after a certain amount of time under ideal conditions is described by the formula: Nt = N0rt Exponential Growth - growth at a constant rate of increase per unit time (geometric) ; has no limit Geometric Rate of Increase: Exponential Growth If 2 adult cockroaches (N) produce 10 offspring each (r) per 3 month period of time (t), the geometric rate of increase can be calculated as follows: time N rate (r) No x r t t1 2 10 2 x 101 (10) = 20 t2 20 10 2 x 102 (100) = 200 t3 200 10 2 x 103 (1000) = 2000 t4 2000 10 2 x 104 (10000) = 20,000 Geometric growth: Nt = N0rt Conclusion: 1 pair of roaches can produce a population of 20,000 roaches in 1 year! ACTIVITY Exponential Growth Activity Linear growth vs. Exponential Growth ACTIVITY Exponential Growth Has Limits because resources are limiting.. So let’s talk about logistic growth & bottom-up regulation Carrying capacity (K) – the population of a species that can be supported in a specific area without depleting the available resources. As resources become scarce and a population nears its carrying capacity, population growth can slow down. Such growth is also referred to as logistic growth and can be represented mathematically as: dN/dt = r N (1 - N/K)  Exponential Growth Always Has Limits: Bottom Up Regulation Carrying capacity (K) – the population of a species that can be supported in a specific area without depleting the available resources. Overshoot – when a population exceeds the carrying capacity of the environment and deaths result from a scarcity of resources. Population crash – a rapid dieback in the population to a level below the carrying capacity. Boom and bust – when a population undergoes repeated cycles of overshoots followed by crashes. Four factors affect growth rate: r = (B + I) – (D +E) Births - the number of births that occur in the population at any give time; rate of births vary by species and also with stress and food availability. Immigration - the number of organisms that move into the population from another population. Deaths - mortality, or the number of deaths that occur in the population at any given time, vary by species and with environmental factors. Emigration - the number of organisms that move out of the population to another population. Factors Affecting Population Growth Density-dependent factors (depends on population density): disease, physiological stress and predation, interspecific competition, intraspecific competition, predator- prey oscillations. Density independent factors (do not depend on population density; often external factors affecting populations): drought, fire, or other habitat destruction that affects an ecosystem. Predator-Prey Oscillations: Density Dependent Factors & Top- Down Regulation Reduce population size by decreasing births or increasing mortality. Interspecific Interactions (between species) Predator-Prey oscillations Is it density-dependent or density- independent? Activity with stress ball Why size matters for populations What is the minimum population size of a rare species required for long term viability? Preserving Populations: Conservation Genetics In a large population, genetic diversity tends to be preserved. A loss/gain of a few individuals has little effect on the total gene pool. However, in small populations small events can have large effects on the gene pool. This is evidenced by genetic drift which is a change in gene frequency due to a random event. Unlike natural selection, genetic drift is random. Genetic Drift in Populations: Two factors that cause it Founder effect occurs when a few individuals start a new population. Demographic bottleneck occurs when just a few members of a species survive a catastrophic event such as a natural disaster Inbreeding may lead to the expression of recessive genes that may have a deleterious effect on the population. Population Viability Analysis Minimum Viable Population - the minimum population size required for long-term survival of a species. The number of grizzly bears in North America dropped from 100,000 in 1800 to 1,200 today. This species range is just 1% of what is once was. It is fragmented into 6 separate populations. Biologists need to know how small the bear populations can be and still be viable in order to save the grizzly. 2016 - USFWS proposed delisting the grizzly from the ESA. Conversations are still going on Grizzly bear distribution in the GYE https://www.cbsnews.com/video/judge-halts-decision-to-allow-grizzly-bear-hunting-in-wyoming-idaho/ from the 1980s through 2014.