Chapter 6 Populations Population Properties The numbers or

Chapter 6 Populations

Population Properties The numbers or population of an organism is limited by their environment Population- all the members of a species living in the same area at the same time Ex: all the oak trees in Houston County

Properties Can be described by: Population size Population Density Patterns of dispersion Demographics Population growth Limits on population growth

Terms to Know Population size- number of individuals present living in a defined area Population Density- number of individuals in a population per unit area Population dispersion or distribution- the spatial arrangement of organisms within a particular area Sex ratio- proportion of males to females

Distribution Patterns Populations may be distributed in different ways: 1. Random- individuals located haphazardly in no particular pattern (minimal interaction) Individuals are independent of others Can occur when resources are found throughout an area

Distributions 2. UNIFORM DISTRIBUTION Individuals are evenly spaced, same distance apart Can occur when individuals hold territories or compete for space Ex: plants in the desert need certain amount of “root” space to get water they need

Distributions 3. CLUMPED DISTRIBUTION Most common in nature Organisms arrange themselves according to the availability of resources Organisms interact and are attracted to certain areas Ex: Bees and flowering plants, breeding pools, humans to urban areas

Distribution Patterns

Age Distribution/Structure Describes the relative numbers of organisms of each age within a population Can make predictions based on age structure Ex: Population past reproductive age will decline over time Population pre-age or at age of reproductionwill likely increase Even age distribution – remain stable

Age Structure Diagrams Survivorship: percent of members likely to survive Growth rate: birth & death rates, change in size Growth rate= birth rate – death rate Rate can be zero (no increase); negative (decrease); or positive (exceeds death rate)

Age Structure Diagram

Graphs

Survivorship Factors Determined by 4 factors: 1. ) Births (natality) 2. ) Deaths (mortality) 3. ) Immigration – arrival on individuals outside the population 4. ) Emigration – departure of individual from the population

Survivorship Types K-selected Devote large amounts of energy and resources to caring for a few offspring Tend to stabilize over time at or near their Carrying Capacity K is abbreviation for Carrying Capacity r-selected Devote their energy and resources to producing as many offspring as possible in a short time Survivorship is left to chance Exponential Growth

Exponential Growth Occurs when a population or anything else, increases by a fixed percentage each year Occurs when pop. has plenty of food, space and limited competition or predators

Limiting Factors Restrain population growth Are: physical, chemical and biological characteristics Carrying Capacity- the maximum pop. size of a species that a given environment can sustain

Carrying Capacity Graph

r-selected vs K-selected

Exponential vs Logistic

Logistic Growth (Curve) (Carrying Capicity) limiting factors = environmental resistance Space, food, water, shelter, disease, predators, temp. mates/breeding sites Plants: sunlight, moisture, soil Aquatic: salinity, sunlight, temp, dissolved oxygen, and pollutants

Limits to Pop. Growth Density Dependent: depends on size of the population Can help find mates, but increases: Factors that occur with the size of the population Competition Increases and decreases with population density Disease and Parasitism Predation

Limits to Pop. Growth Density Independent Limiting factors that affect the population regardless of size (density) Can eliminate large #’s of individuals without regard to their density Examples: Climate/Temperatu re extremes Natural/Catastrophi c events or disasters Human Activity

Chapter 6: Communities Species Interactions and Community Ecology

Organisms Niche § Includes species habitat use, its role in the community, consumption of foods, use of resources, role in food chain/food web, and it’s interactions with other organisms § Summary of everything an organism does in its environment

Types of Niches u Fundamental Niche u Realized Niche u The full niche of a species u Plays only a part of its (species) role u No competitors u Forced to use fewer resources due to competition or other species interactions u Fulfills all its roles or uses all resources it can and capable of using u Competitors restrict what an organism can do or what resources it can use u Chart – Fig. 6. 2, pg. 143

Species Relationships v When 2 organisms living in close association with each other interact = Symbiotic relationship v In symbiosis, at least one of the organisms usually benefits from the relationship

Species Interactions Ø Types: Ø Competition Ø Predation Ø Parasitism Ø Herbivory Ø Mutualism Ø Commensalism/Amensalism

Competition v Occurs when more than one species is seeking or attempting to use the same limited resource v Can take place in 2 ways: v Intraspecific Competition – competition among members of the same species v Interspecific Competition – competition among members of two or more different species

Consequences of Competition Exclusion – when one species excludes another species from resource use entirely Species Coexistence – when neither species fully excludes the other, live in equilibrium; *use resources at different times of the day or different levels Resource Partitioning – the species partition or divide the resources they use in common Character displacement – evolve physical characteristics that reflect their portion of resource use, natural selection; *Ex: birds eat same type of seed – one eats the smaller, the other the larger seeds Larger seeds = bigger beak; Smaller seeds = smaller beak (Darwin’s Finches)

Predation v Process in which a (predator) hunts, captures, kills, and eats another organism(prey); *one benefits/one harmed v The primary organization forces and influence in community ecology v These interactions structure/influence food chains/webs, community make up, numbers and abundance of the predator and prey; creates cycles in populations

Predation

Adaptations of Predation v Camouflage: blending in with environment v Warning coloration: black stripes or red, orange and yellow v Mimicry: imitates another organisms warning coloration v Protective covering: quills, shells, exoskeleton v Odors/Poisons/Inks: skunks, snakes, octopus v Flying

Parasitism v Relationship in which one organism (parasite) depends on another (host) for nourishment, while doing the host harm v Some parasites cause little harm, while others kill v Some parasites live in close contact with the host; ticks, tapeworm, and lampreys v Others are free-living and come into contact with the host infrequently

Herbivory * When animals feed on the tissues of plants v Insects that feed on plants are the most widespread type v Some plants recruit animals as allies to help in defense

Mutualism v. Relationship in which 2 or more species benefits from the interaction with each other v. Bacteria in our intestines v. Acacia trees and ants – trees provide shelter, the ants defend and protect the trees

Commensalism and Amensalism v Commensalism: one species benefits, the other is neither harmed or helped (unaffected); *Sharks and remora’s: remora’s attach to sharks and feed on scraps of food; clown fish/sea anemome v Amensalism: one species is harmed and the other is neither harmed or helped (unaffected); *Ex: black walnut tree that secretes chemical that kills neighboring plants, penicillin/bacteria

Ecological Communities v Energy passes through Trophic Levels v As organisms feed on one another, energy moves through the community v Producers = 1 st level v Primary consumers = 2 nd level; herbivores v Secondary consumers = 3 rd level; eat primary consumers v Tertiary consumers = 4 th and up; eat 2 nd and 3 rd

Energy/Biomass v Food webs: show relationships and energy flow v Keystone species: strong impact on community; secondary and tertiary consumers v Community that resists change and remains stable; shows resistance v A community that changes in response to disturbance then returns to original state; shows resilience