Lecture 18: Introduction to Ecology & Populations PDF

Lecture 18. Introduction to Ecology & Populations Ecology – study of how organisms interact with their biotic & abiotic environments Biotic factors in environment – living thing or something that derives from a living thing (i.e., organic matter) B livingthings Bi...

Lecture 18. Introduction to Ecology & Populations Ecology – study of how organisms interact with their biotic & abiotic environments Biotic factors in environment – living thing or something that derives from a living thing (i.e., organic matter) B livingthings Biotic factors in environment – living thing or something that derives from a living thing (i.e., organic matter)  A pyecial not lung Abiotic factors in environment – things that are physical rather than biological; not living or derived from a living organism Abiotic factor – Soda Springs – Tuolumne Meadows – Yosemite Which features are abiotic & which are biotic in this landscape? Abbott’s Lagoon, Pt. Reyes Nat’l Seashore, Marin Co., CA Distinction between abiotic & biotic features of environment is not always clear – e.g., soil  Ecological systems exist in BIOSPHERE a hierarchy of organization * Ecological system – system BIOME formed by interactions between organisms & their environment ECOSYSTEM Hierarchy – systematic organization of living things into levels of complexity or COMMUNITY inclusiveness Hierarchy of organization in POPULATION living systems: individual  population  community  ecosystem  biome  biosphere INDIVIDUAL IPCEBB Biological hierarchy – Terms Individual – individual organism Population – individuals of same species that occupy the same area & have potential to interbreed Community – populations of different species living together in a particular area – have the potential to interact Ecosystem – one or more communities of organisms & the physical (abiotic) environment around them Biome – any of Earth’s major ecosystem types – contains communities of - organisms with similar adaptations Biosphere – all ecosystems on Earth Population ecology – study of how individuals in a population of a single species interact with their environment – focuses on factors that in6luence population density & population growth Community ecology – study of how interactions between multiple species affect community structure & organization - one rando/mutipic Population of gannets Community of species in tide pool Populations experience the same environmental factors, rely on the same resources, & can interact & breed together Members of this population of northern fur seals would experience more similar environmental conditions with each other than they would with members of other populations of northern fur seals Environmental conditions include abiotic & biotic factors Population distribution – geographical area occupied by a population Population distributions are determined by population density areh Geographic range Distribution of species = species’ geographic range Species’ geographic range = sum of distributions of all populations of a species Right: geographic range of Tetraphis moss (Forman 1964) hour the spaies distribute is eque to gryace large Populations are characterized by number & distribution of individuals Population density – no. of individuals of species per unit area or per unit volume – e.g., number of oak trees per square kilometer (km2) 2m 2m Area = 2m X 2m = 4m2 Density = 12 indiv/4m2 = Density = 4 indiv/4m2 = 3 indiv/m2 1 indiv/m2 poplatyarea poplason devity no is the of ranel per specie Methods for estimating population size - 100 - Mark-recapture method for estimating population size Each block represents one fish in a lake Total number of blocks = total number of fish Yellow blocks represent fish that have been caught & marked Mark-recapture method Scenario: you want to estimate the total number (N) of fish in a lake (N is unknown) You catch a sample of 16 fish & mark them Sample 1: 16 200 offspring per lifetime)  model that as its environment animited remorse of Exponential growth model assumes ideal environment with unlimited resources Idealized situations (models) help us understand: Capacity of species to increase Conditions that facilitate unlimited population growth Ideal conditions necessary for exponential growth are approximated in certain situations – rabbits in Australia had virtually unlimited resources Natural predators of European rabbits like European polecat (right), badgers, buzzards, etc. absent in Australia. Carrying capacity (K) – maximum average population size that can be sustained by - limited resources of an environment K limits growth Logistic growth in lab populations Georgii Gause – Russian ecologist – experimented with population growth in paramecia (1934) Logistic growth in paramecia Gause raised populations of two species of paramecia in Xlasks of broth Both species exhibited logistic growth – food became limited as population size increased Because they were competing for the same limited food source, one - species (P. caudatum) always went extinct More on Gause competition later…  Logistic growth in natural populations Northern fur seals on St. Paul’s Island, Alaska RUSSIA ALASKA St. Paul’s Island St. Paul’s Island, Alaska Seal populations in Pribilof Islands (Alaska) had numbered in millions before fur trade Fur trade accelerated in late 1700s (~2.5 million seals killed from 1786–1867) Sealers on St. Paul’s Island – 1890s By 1912, seal population in Pribilof Islands reached a low of 216,000 Image: MW Bruce Beginning in early 1900s, hunting was regulated – seal population on St. Paul’s Island rebounded Northern Fur Seal population experienced logistic growth Logistic growth model – limiting factors eventually slow population growth ↓ Limiting factors: limited food, limited space, etc. Populations experience logistic growth when resources are limited We saw the same pattern with Gause’s paramecia Logistic growth model Population growth = 0 when birth rate = death rate When birth rate = death rate (& population growth = 0), population has reached carrying capacity (K) - Carrying capacity (K) – maximum average population size that can be sustained by limited resources of an environment K is an average population size Populations often overshoot carrying capacity (followed by collapse) before stabilizing around mean population size - Logistic growth model – limiting factors eventually slow population growth Begins with period of rapid (exponential) growth – curve is J-shaped until ca. 1930 Seals were protected from unregulated hunting Seal population rebounded from ~1000 to ~7500 Competition is very low when period of exponential growth population size is small Logistic growth model – limiting factors eventually slow population growth Growth slowed from ca. 1930 onward – curve bends J-shaped curve changed to an S- shaped curve Population size stabilized around an average of ~9500 K ~ 9500 lopstic Some Logistic Growth (S-shaped curve) K = 9500 At K, B = D Population growth = 0 Population size = 9500 Which limiting factor(s) caused population growth to slow in this case? jet Carrying capacity can vary between different habitats & can change in the same place if biotic or abiotic factors affect the amount of available resources Drought – Uttarakhand, Northern India  - Carrying capacity can increase for a population if resources increase – may lead to range expansion Feeding & planting of flowering plants led to increase in K in areas occupied by Anna’s hummingbirds Populations in these areas eventually exceeded K Dispersal of surplus individuals away from existing populations  established new populations People began to see hummingbirds in their area & put out hummingbird feeders K increased in new area (etc.) Can you think of other organisms that might have experienced an increase in carrying capacity due to an increase in human-related resources?  1100 1000 900 POPULATION SIZE 800 700 600 - 500 400 300 200 100 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 DAY In which period was competition the lowest? 678 In which period was competition the greatest? h 1011 Between which two days do you observe the greatest change on the y-axis? Why was the change on the y-axis greatest at that point?