Population Dynamics/Density & Life Histories

Populations

groups of individuals of the same species that live in the same area & have the same potential to interbreed

Metapopulations

groups of pops connected by dispersal (immigration/emmigration)

Endemic

species restricted to only certain locations (and nowhere else on earth)

Population dynamics are controlled by

Physical environment, Biological interactions, and Dispersal

Intraspecific interactions

comp for resources by individuals of the same species

Interspecific

comp over resources, predation, herbivory, across diff species

Active dispersal

mvmt controlled by individual

Passive dispersal / Active agent

mvmt controlled by the physical environment / birds dispersing seed-laden fruits

Migrations

specific type of dispersal that occurs in response to seasonal variation in resources / involves round-trip mvmt, not necessarily by same individual / usually includes the entire pop

Full census

a count of every individual in a pop / challenging in large pops whose full ranges are not known

Population density

direct count of subset of individuals in the pop w/in a certain area —> extrapolate to estimate total pop size

Area-based survey

sample w/in defined areas (plots/blocks) / ideal for sessile organisms

Line-transect survey

sample along a defined line w/in a pop’s range / ideal for sessile

Mark-recapture

capture, mark, & release several individuals in a pop; repeat after some time w/another subset to estimate total pop size in sampling area

Exponential population growth

J-shaped curve / assuming continuous pop growth, nearly impossible in nature

Logistic population growth

S-shaped curve / assume that b & d are dependent on pop density (intraspecific comp) / As pop (N) increases, r decreases towards zero, pop levels off at carrying capacity

Carrying capacity (K)

number of individuals in a pop that can sustain a particular environment

Density-dependent factors that limit pop growth

Limiting resources (more comp as pop^), Predation (^pop attracts more preds), Pathogens (faster spread)

Allee effect

when higher densities are better / some pops grow better (up to a limit) when density is high = better survival as a group / Protection (zone of protection for prey), Dilution effect (reduces risk of disease transmission), & Predator detection (large groups=less vulnerable)

Type I survival curve

High overall survivorship through adulthood, steep decline w/age / in many large mammals

Type II survival curve

constant risk of mortality at all ages / in many birds, fish, & plants

Type III survival curve

low survivorship early in life, higher during maturity / in most insects & annual plants

Life histories

describe the lifetime pattern of growth, reproduction, & survival / each species has a life history strategy

Semelparity

reproduces only once & then dies, lots of small seeds, shorter lifespan, probability of dying remains high when adulthood is reached

Iteroparity

reproduces multiple times, fewer seeds but larger, live longer

“FAST” life history

faster growth, exponential growth periodically, earlier reproduction, greater # of offspring, smaller parental investment, low offspring survival, shorter life span, typically type III curve

Includes semelparous species / Tolerate unpredictable conditions

“SLOW” life history

slower growth, pop usually around K, later reproduction, fewer offspring, greater parental investment, high offspring survival, longer life span, typical type I curve

Includes iteroparous species / Thrive in predictable conditions

Biological controls

use natural enemies to reduce pop density of economically damaging species, can becomes pests themselves bc they have no natural preds