Lesson 4: Population and Community Ecology

Lesson 4: Population and Community Ecology DR. MAE ANGELINE T. TAJOLOSA COURSE FACILITATOR  Humans have always been one of the greatest factors in the degradation of energy resources. The use of resources in the community is vastly affected by the growth of size of pop...

Lesson 4: Population and Community Ecology DR. MAE ANGELINE T. TAJOLOSA COURSE FACILITATOR  Humans have always been one of the greatest factors in the degradation of energy resources. The use of resources in the community is vastly affected by the growth of size of population of living things. Studying the degree of this growth may serve as a warning of what would happen in the future if living things especially humans will continue to increase their population dramatically. Lesson Outcomes At the end of the lesson, you must have: 1.defined and differentiated population and community ecology 2.identified the factors that affect the population growth 3.described interactions between and within species in a community 4.calculated the index of diversity based of species richness and relative abundance  Engage In your own understanding, What is Population? What is Community? Explore Watch the video link and answer the guide questions.  Organism, Population, Community: What is the difference? https://www.youtube.com/watch?v=ClLHcSXzRos Population Ecology  I.Population Ecology Population in human demography is a set of humans in a given area. In genetics, Population is a group of isolated interbreeding individuals. Population ecology is a group of similar species living in a certain place at the same time. Examples would be all the cats in the house, all the maya birds in the campus, all the narra tree in a province, all the tilapia in the Philippines and all the bees in the world. Levels of complexity Individual/ Organism Population – same species, same time, same area Community – all the different populations in an area Ecosystem – all the different communities plus the abiotic factors in an area Biosphere – all areas on Earth where life exists Basic population characteristics Population size = total number of individuals (N) Population density = number of individuals per unit of area Helps us understand if the species is rare or abundant Population distribution = how individuals are spaced relative to others in the population Random – no pattern of location (trees in a forest) Uniform – fairly even spacing (nesting birds) Clumped – individuals gather around each other (schooling fish) Population sex ratio = the ratio of males to females Usually 50:50 Population increase is related to the number of females Population age structure = the number of individuals in each age category Populations with large numbers of young  increasing Populations with large numbers of old  decreasing  PRIMARY FACTORS THAT DETERMINE THE POPOLATION SIZE Input Output Immigration Emigration & Population size & Births Deaths Factors that influence population size Density-dependent factors Influence an individual’s odds of survival in a manner that depends on the size of the population Example: available food These factors are also called limiting resources The population limit in an ecosystem is its carrying capacity Factors that influence population size… Density-independent factors Have the same effect on an individual’s odds of survival regardless of the size of the population Example: a tornado Population growth models Exponential growth model Growth rate = number of offspring – deaths Under ideal conditions (with unlimited resources) each species has a particular intrinsic growth rate – the max for that species This model calculates this maximum rate and displays it as a J-shaped curve (because there are no limits) Only beginning populations can actually show this type of growth Population growth models… Logistic growth model Includes environmental limits on the population growth As the population reaches the carrying capacity, the growth slows and then stops This produces an S-shaped curve Some populations cycle above and below the carrying capacity – this is overshoot followed by die-off Reproductive strategies K-selected species Low intrinsic growth rate Slowly reach the carrying capacity and then stay there Characteristics: Large Later maturing Few offspring Substantial parental care Population growth models… r-Selected Species High intrinsic growth rate Rapid population growth followed by overshoots and die-offs Characteristics: Small Early maturity Small offspring Little or no parental care Survivorship Curves Patterns of survival over time: Type I – high survival throughout most of their lifespan K-selected species: humans, elephants Type III – low survival early in life; few individuals reach adulthood r-selected species: mosquitoes, dandelions Type II – relatively constant decline in survivorship throughout their lifespan squirrels, coral Survivorship Curves… Metapopulations Smaller, fragmented parts of a larger overall population Occasionally members of one metapopulation move from one to the other This can reduce the risk of extinction: Moving individuals increase genetic diversity as well as the size of a population Human development is causing more and more metapopulations to form COMMUNITY ECOLOGY There are several populations in an area. In a grassland, one would find populations of grasshoppers, frogs, snakes, grasses, herbs and shrubs and many others. Together, all these populations would form an ecological or biotic community. In other words, Community Ecology is the study of the organization and functioning of communities, which are assemblages of interacting populations of the species living within a particular area or habitat. VI.Community Interactions Interspecific interactions affect the survival and reproduction of the species that engage in them. These interactions can be grouped into three broad categories: competition, exploitation, and positive interactions.  Interaction Description Competition (-/-) Two or more species compete for a resource that is in short supply. Example: Rice and weeds competing for light and nutrients found in soil. Exploitation (+/-) One species benefits by feeding upon the other species, which is harmed. Exploitation includes the following: One species, the predator, kills and eats the other, the prey. Predation Example: Snake(predator) eating a bird (prey). An herbivore eats part of a plant or alga. Example: Cow(herbivore) eating grass. Herbivory The parasite derives its nourishment from a second organism, its host, which is harmed. Example: A leech is found feeding on a frog's blood Parasitism Positive interactions (+/+ or 0/+) One species benefits, while the other species benefits or is not harmed. Positive interactions include the following: Both species benefit from the interaction. Example: Clownfish Mutualism (+/+) live within the protective tentacles of the sea anemone. In return, the sea anemone receives cleaning and protection. One species benefits, while the other is not affected. Example: Cattle egrets eat the insects stirred up by cattle when they are Commensalism (+/0) grazing. The cattle are unaffected, while the birds gain food. Community Interactions… Predation - the use of one species as a resource by another Four categories: 1. True predators – kill and eat their prey 2. Herbivores – consume plants as prey; typically only eat some of the plant; rarely kill the plant 3. Parasites – live on or in a host organism; rarely causes the death of their host Pathogen – disease-causing parasite 4. Parasitoids – lay eggs inside another organism  Competition  Doesn't involve always the same species, but it is more severe among the same numbers of species because they have common needs. Community Interactions Competition Individuals must ‘fight’ over the same limiting resource Competitive exclusion principal Two species competing for the same limiting resource cannot coexist Resource partitioning Two species divide the resource based on differences in behavior or morphology This can lead to natural selection which over time will increase the differences between the 2 species Three possibilities: 1. Temporal resource partitioning – use the same resource but at different times (coyotes and wolves) 2. Spatial resource partitioning – use different locations (plants with shallow roots vs. deep roots) 3. Morphological resource partitioning – evolution of different body plans to use different parts of the resource (Darwin’s finches) Resource partitioning Community Interactions… Mutualism – two species interacting in a way that increases the survivability of both Plants and the insects that pollinate them Acacia trees and ants Commensalism – one species benefits from an association with another but the other is not helped nor harmed Birds nesting in trees Keystone Species The species on which the ecosystem stability depends – removing it leads to instability:  Food supply species  Predator-mediated competition – the predator keeps the numbers of the superior competitor in check. Without the predator, the competitor over- populates the ecosystem (sea stars)  Ecosystem engineers – create habitat for other species Keystone Species… Changes in communities over time Ecological succession – predictable replacement of one group of species by another Two types: 1. Primary succession – occurs only on surfaces without any soil (new volcanic area; abandoned parking lot) 2. Secondary succession – occurs in disturbed areas that have not lost their soil – the original vegetation has been removed as in a forest fire or even abandoned farmland Pioneer species – plants that are able to colonize new areas at the early stages of succession. They grow rapidly and need lots of sunlight Climax community – the later stages of succession. Generally considered to be the ‘typical’ type of community for that biome  VII. Species Diversity Species Diversity of a community is the variety of different kinds of organisms that make up the community. It has two components: the species richness and relative abundance. Species richness is the number of different species in the community. Relative abundance of the different species is the total number of individuals of a species in relation to the total number of individuals of all species in a given area or community.  Imagine two small forest communities, each with 100 individuals distributed among four tree species (A, B, C, and D) as follows: Community 1: 25A, 25B, 25C, 25D Community 2: 80A, 5B, 5C, 10D The species richness is the same for both communities because they both contain four species of trees, but the relative abundance is very different. Relative abundance= Total # of individuals of a species Total # of individual of all species In community 1, the relative abundance of species A is 0.25 Relative abundance=25/100=0.25 In community 2, the relative abundance of species A is 0.8 Relative abundance= 80/100= 0.8  Ecologists use many tools to compare the diversity of communities across time and space. They often calculate indexes of diversity based on species richness and relative abundance. One widely used index is Shannon diversity (H): H = -(pA ln pA + pB ln pB + pC ln pC + c) where A, B, C... are the species in the community, p is the relative abundance of each species, and ln is the natural logarithm; the ln of each value of p can be determined using the “ln” key on a scientific calculator. A higher value of H indicates a more diverse community. Let’s use this equation to calculate the Shannon diversity index of the two communities  For community 1, p = 0.25 for each species, so H = - 4(0.25 ln 0.25) = 1.39. For community 2, H = -[0.8 ln 0.8 + 2(0.05 ln 0.05) + 0.1 ln 0.1] = 0.71. These calculations confirm our intuitive description of community 1 as more diverse.  Elaborate Compute the index of diversity 1. Grassland 1 has 100 individuals distributed among four species: 20A, 25B, 25C, and 30D. Grassland 2 has 100 individuals distributed among three species: 80A, 15B, and 5C. Calculate the Shannon diversity (H) for each grassland. Which is more diverse? Factors affecting species richness Latitude: equator to poles  number of species declines Time: longer areas have been around more species Habitat size: larger habitat area  more species Distance from other habitats: increase distance  fewer species THANK YOU.....