Chapter 6 Population and Community Ecology

New England Forests Come Full Circle 1620 Over next 200 years – settlers Deforestation peaked in 1800s – 80% of New England forests were cleared Bw Abandoned farmland slowly recovered – resilient area This created an ever-changing ecosystem

Nature exists at several levels of complexity

Population Ecologists Study the Factors that Regulate Population Abundance and Distribution Population ecology – the study of factors that cause populations to increase or decrease Why is this important?

Population Characteristics Population size (N)- the total number of individuals within a defined area at a given time Population density- the number of individuals per unit area at a given time Population distribution- how individuals are distributed with respect to one another

Population Characteristics Population sex ratio- the ratio of males to females Population age structure- how many individuals fit into particular age categories

Factors that Influence Population Size Density-dependent factors- the size of the population will influence an individual’s probability of survival Gause Limiting resource Carrying capacity (K) Density-independent factors- the size of the population has no effect on the individual’s probability of survival

Population Growth Rate Population growth models Growth rate - the number of offspring an individual can produce in a given time period, minus the deaths of the individual or offspring during the same period Intrinsic growth rate - under ideal conditions, with unlimited resources, the maximum potential for growth Under less ideal conditions

Exponential Growth Model Exponential growth model formula What results?  J-shaped curve However…

Logistic Growth Model Logistic growth- when a population whose growth is initially exponential, but slows as the population approaches the carrying capacity Produces - S-shaped curve Problem

Variations of the Logistic Model Populations do not always level off at carrying capacity Overshooting K – population becomes larger than the K Result? Ie. reindeer on St. Paul Island in Alaska

From Environment: Boom-Or-Bust Population Cycles Boom-or-Bust Population Cycles Not well understood Ie. Lemmings and red grouse populations

Population Oscillations Predator-Prey Relationships Lynx and Hares (R) Wolves and moose

Reproductive Strategies K-selected species- the population of a species that grows slowly until it reaches the carrying capacity. Ex. elephants, whales, and humans R-selected species- the population of a species that grows quickly and is often followed by overshoots and die-offs Ex. mosquitoes and dandelions

Survivorship Curves Species have different patterns of survival over time 3 basic curves: Type I Type II Type III

Metapopulations Metapopulations- a group of spatially distinct populations that are connected by occasional movements of individuals between them Movement via corridors Connections important

Community Ecology Factors to determine distribution of species: Species’ fundamental niche Ability to disperse to an area Interactions with other species Community ecology – study of the interactions of organisms which determine the survival of a species in a habitat

Competition Competition- the struggle of individuals to obtain a limiting resource Gause’s Competitive Exclusion Principle

From Environment: Anoles in FL Example Green Anole and Brown Anole Fundamental niches of 2 lizards initially overlapped Brown anole eventually out-competed the green anole  reduced the green anole’s realized niche

Resource Partitioning Resource partitioning – when 2 species divide a resource based on differences in the species’ behavior or morphology Species in nature reduce resource overlap via: Temporal resource partitioning Spatial resource partitioning Morphological resource partitioning

Predation Predation- the use of one species as a resource by another species Organisms of all sizes can be predators Predators can be grouped: True predators Herbivores Parasites Pathogens – parasites that cause disease Parasitoids Awesome video:

Mutualism Mutualism- A type of interspecific interaction where both species benefit Examples: Plants and pollinators Image – Acacia trees and ants Lichen Coral reefs

Commensalism Commensalism- a type of relationship in which one species benefits but the other is neither harmed nor helped Examples…

Overview of Interspecific Interactions Symbiotic relationship – relationship of 2 species that live in close association with each other Includes: commensalism, mutualism and parasitism

Keystone Species Keystone species- a species that plays a role in its community that is far more important than its relative abundance might suggest Usually not the most abundant or major energy producers Roles include: Predators Sources of food Mutualistic Providers of some other essential service

Keystone Species The Gray Wolf Where wolves were hunted to extinction  populations herbivores increased explosively Caused overgrazing  some plant species disappeared Many insects were lost Indiana and Montana- hunting of gray wolf ok…

Primary Succession Primary succession- occurs on surfaces that are initially devoid of soil Process: Bare rock is colonized by organisms  secrete acids

Secondary Succession Secondary succession- occurs in areas that have been disturbed but have not lost their soil Follows events like: forest fires, hurricanes, abandoned fields

Climax Stage Climax stage (community) – the community scientists used to believe ended succession Characteristics: Complex structures – many species interactions Narrow niches High species diversity

Aquatic Succession Lakes are filled with sediment Slowly become terrestrial habitat Explain the process

Factors that determine species richness: Latitude Time Habitat size and distance from habitat from source of colonizing species Basis for the Theory of Island Biography (next slide)

Theory of Island Biogeography Theory of island biogeography- the theory that explains that both habitat size and distance determine species richness Larger habitats contain more species Why? Further from colonizing community  the less species