Chapter 9 Population Dynamics, Carrying Capacity, and Conservation Biology
9-1 Population Dynamics & Carrying Capacity Populations change in response to enviromental stress or changes in evironmental conditions These changes are called population dynamics
Biotic potential is maximum rate of growth for a population without any resistance Intrinsic rate of increase (r): rate at which a population would grow if it had unlimited resources Depends on having a certain minimum viable population size (MVP) If a pop. declines below the MVP then the intrinsic rate of increase falls and extinction is likely. No population can grow indefinitely always limits to pop. growth
Factors Affecting Population size Density- Dependent (biotic factors; have to do with other living things) Interspecific factors: in symbiotic relationships population size and growth curves related Intraspecific factors: overcrowding, stress Density-Independent (abiotic factors; no regard to population size) Immigration, emigration, pronatalist pressures
Environmental resistance All of the factors that act jointly to limit population growth is environmental resistance. Together biotic potential and environmental resistance determine the carrying capacity (K) K: the number of individuals of a given species that can be sustained in a given space
Exponential vs. Logistic A population with few resource limitations grows exponentially Gives J-shaped growth curve
Logistic growth Involves exponential growth when there is a steady decrease in pop. growth as the pop. encounters environmental resistance and approaches carrying capacity and levels off. S-shaped curve
Arithmetic Growth Population growth that increases by a constant amount over time. Same number is added to the previous (ex: 0,2.4,8,12) A town would experience this type of growth if it increased by 100 people every year regardless of size. Not common unless birth rate and death rates are balanced
What kind of curves do we find in nature? 4 general types of population fluctuations: 1) stable: species pop. fluctuates slightly above and below its average K 2) irrupt: may occasionally explode to a high peak and then crash to a more stable level or very low level 3) chaotic behavior: no recurring pattern; irregular 4) cyclic fluctuations: pop. rise and fall on 10 yr. cycle
Role of Predation in Pop.Size Predator-prey interactions generally follow a cyclic population cycle Leading explanation for the 10-year population cycle of the snowshoe hare and its predator Canadian lynx.
Control of lynx and hare 1) Top-down control Lynx preying on hares periodically reduce their population Shortage of hares reduces lynx population Allows hare population to build up again 2) Bottom-up control Large # of hares die when they consume plants faster than can be replenished Hare pop. crashes, plants recover, hare pop. rises again in a hare-plant cycle. So instead of lynx controlling hare, the changing hare pop. cause fluctuations in the lynx.
9-3 Reproductive Patterns and survival Species reproduce one of two ways: 1) Asexual offspring exact genetic copies of a single parent common in single-celled species 2) Sexual produce offspring by combining gametes from two parents
What types of patterns do species have? 2 reproductive patterns: r-selected K-selected Based on 1) their position on the S-curve 2) the characteristics of their reproductive patterns
r-selected species Species with a capacity for a high intrinsic rate of increase (r) Bacteria, algae, rodents, annual plants and insects Spend most of their energy on reproduction Have many offspring each time Reach reproductive age rapidly Have short generation times Give little or no parental care or protection Short lived (life span less than 1 yr) Also known as Opportunists species
r-selected cont.. Once established, their populations may crash b/c 1) Changing or unfavorable conditions 2) Invasion by a competitive species For these reasons, most r-selected species go through irregular and unstable cycles To survive, must continually invade new areas to compensate for being displaced
These species K-selected species 1) Put little energy into reproduction 2) Reproduce later in life 3) Have few offspring with long generation times 4) Most of their energy goes to nurturing and protecting their young Offspring of these species 1) develop inside their mothers 2) are large and mature slowly 3) are cared for and protected by parents
K-selected species cont.. Also known as competitor species b/c do well in competitive conditions when their pop. size is near (K) carrying capacity Ex: large animals, birds of prey, large and long lived plants Many are prone to extinction Follow logistic growth curve Thrive in stable conditions
Survivorship curves Represents the age structure of a population and shows the number of survivors of each age group 3 types Late loss curves: K-selected species Early loss curves: r-selected species Constant loss curves: species with intermediate reproductive patterns (constant threat from starvation, predation, disease) Ex: songbirds, lizards, small mammals
9-4 Conservation Biology Developed in 1970 s Uses the best available science to take action to preserve species and ecosystems Seeks to answer 3 questions: 1) Which species are in danger of extinction 2) What is the status of the functioning of ecosystems and what ecosystem services are we in danger of losing 3) What measures can we take to help sustain ecosystem functions and viable populations
Conservation biology has 3 underlying principles: Biodiversity is necessary to all life on earth Humans should not cause or hasten extinction or disrupt vital ecological processes Best way to preserve is to protect intact ecosystems Conservation biology is based on Aldo Leopold s ethical principle
Bioinformatics Efforts of conservation biologists focused on building computer databases about biodiversity Bioinformatics provides tools for storage and access to key biological info and builds databases that contain needed biological info