Week 3: Population Biology: Understanding Populations as the Unit of Evolution; How to Study Populations

early reproduction

Organisms that reproduce early in their lifetimes likely produce more offspring, but it is often at the expense of the parent. Advantages: • More reproductive events over a lifetime • Higher number of offspring overall Disadvantages: • Energy diverted from growth and survival • Parent may have shorter lifespan or reduced health

pros and cons of Iteroparity

Spreads reproductive risk over multiple years, ensuring survival in fluctuating environments. • Allows for parental care, improving offspring survival. • Flexibility to reproduce more or fewer times depending on conditions.

Disadvantages of Iteroparity: • Requires sustained energy investment over a longer lifespan, potentially reducing lifespan or health. • Lower reproductive output in any single reproductive event compared to semelparous organisms.

Population Ecology

•The study of population ecology focuses on the number of individuals in an area and how and why population size changes over time.

•We study these changes in #'s of individuals in a population by understanding population characteristics.

We can characterize individual populations in terms of their

•Size

•Density

•Factors Affecting Density

•Patterns of Dispersion

•Rates of growth (or decline)

•Limits on growth

Population Fluctuations

Populations fluctuate based on several factors: Seasonal changes + Natural disasters - volcanoes, fires, hurricanes, etc. + Competition for resources

Demography

-uses a series of mathematical tools to investigate how populations respond to changes in their biotic and abiotic environments

-Demography is the statistical study of population changes over time: birth rates, death rates, and life expectancies.

Quadrat Method

when you calculate the # of plants in specific area and multiply it by the total area

Mark and Recapture

1. Individuals are is captured, counted, and marked.
2. Then they are released back into the population
3. Another group is captured later.
4. Ratio of marked to unmarked individuals helps estimate the total population size.

Organismal Ecology

Study of the adaptations that enable individuals to live in specific habitats (can be morphological, physiological, and/or behavioral)

Population Ecology

Study of a group of interbreeding organisms that are members of the same species (conspecifics) living in the same area at the same time

Community Ecology

Study of the processes driving interactions and their consequences amongst different species within an area (typically a 3-D space)

Ecosystems Ecology

Study of all of the biotic components (living things) in an area along with the abiotic components (nonliving things) of that area, and how nutrients and energy are stored and moved among organisms and through the surrounding atmosphere, soil, and water

Transect Method

This can be used when the study site has sloping topography. This is used to study the zonation pattern of vegetation in sloping study sites. This method could be used also in aquatic ecosystem.

A higher population density or a clumped dispersion pattern

Results in more potential reproductive encounters between individuals, which can increase birth rate

A female-biased sex ratio (the ratio of males to females) or age structure (the proportion of population members at specific age ranges) composed of many individuals of reproductive age...

Increased birth rates

Life Tables

Life tables divide the population into age groups and show how long members of that group are likely to live.

Survivorship curves

graphs of distinct patterns of survival over time

Survivorship curves Type 1:

Type I:

Characteristics: High survival rates during early and middle years, with most deaths occurring in older age.

Example: Humans and most primates.

Reproductive Strategy: Usually have few offspring and provide extensive parental care to ensure survival.

Survivorship curves Type 2:

Type II:
Characteristics: Constant mortality rate throughout life; individuals die at a relatively uniform rate across all age intervals.
Example: Birds.
Reproductive Strategy: Generally have few offspring and offer significant parental care.

Survivorship curves Type 3:

Characteristics: Very high mortality rates in early life stages, with those surviving to old age having a higher chance of living a longer life.
Example: Trees, marine invertebrates, most fishes.
Reproductive Strategy: Produce a large number of offspring but provide minimal parental care. The high number of offspring ensures that enough survive to maintain the population.

Life Histories

A species' life history describes the series of events over its lifetime, such as how resources are allocated for growth, maintenance, and reproduction.

Late Reproduction

Organisms that reproduce late in life may be able to better provide for themselves and their offspring, but they risk not surviving to reproductive age.. Advantages: • More energy invested in growth and survival. • Once they are mature, they can reproduce as much as it is possible for the species • Better care for offspring (but not all provide parental care) Disadvantages: • Risk of not surviving to reproductive age. • Fewer offspring overall.

Semelparity

occurs when a species reproduces only once during its lifetime and then dies.

Iteroparity

describes species that reproduce repeatedly during their lives.

pros and cons of semelparity

Advantages of Semelparity: • Maximizes reproductive effort: All available energy and resources are directed toward a single, massive reproductive event, leading to a large number of offspring. • High offspring production: Producing many offspring at once increases the chance that at least some will survive, especially in unpredictable environments. • Overwhelms predators: By producing offspring in large numbers (e.g., periodical cicadas), predators cannot consume them all, ensuring the survival of many.

Disadvantages of Semelparity: • No second chances: If the single reproductive event fails due to poor conditions or predation, the organism does not have another opportunity to reproduce. • High risk of reproductive failure: Semelparous species are more vulnerable to sudden environmental changes, as they rely on one successful event for reproductive success. • High energy investment leads to death: The massive energy expenditure for one reproductive event usually leads to the death of the organism, limiting its potential longterm reproductive success.

Populations

consist all individuals of the species living within a specific area

A community

is the sum of populations inhabiting an area

An Ecosystem

consists of all the living things in a particular area together with the abiotic, nonliving parts of the environment (nitrogen in soil, rainwater, rocks, etc.)

The Biosphere

is the collection of all ecosystems, and it represents all zones of earth

Population size (N):

the total number of individuals

Population density

the number of individuals within a specific area.

Direct Counting

is a population Research Methods

Species Distribution

Species dispersion patterns (or distribution patterns) show the spatial relationship between members of a population within a habitat at a particular point in time.

Demography: Population Dynamics

Stable Population: When the birth rate and death rate are equal, the population size remains constant over time.

Increasing Population: When the birth rate exceeds the death rate, leading to a rise in the number of individuals in the population.

Decreasing Population: When the death rate exceeds the birth rate, resulting in a decline in the number of individuals in the population.

Life Histories: Energy Budgets

Energy is required by all living organisms for their growth, maintenance, and reproduction.

Energy is often a major limiting factor in determining an organism's survival.

All species have an energy budget: they must balance energy intake with their use of energy for metabolism, reproduction, parental care, and energy storage.

Life History: Fecundity

Fecundity is the potential reproductive capacity of an individual within a population.

Fecundity describes how many offspring could ideally be produced if an individual has as many offspring as possible, repeating the reproductive cycle as soon as possible after the birth of the offspring.

In animals, fecundity is inversely related to the amount of parental care given to an individual offspring

High Fecundity

Animals with high fecundity are often self-sufficient at a very early age. • Their energy is used for producing offspring instead of parental care. • Offspring have some ability to be able to move within their environment and find food and perhaps shelter

Low Fecundity

Animal species that have few offspring (low fecundity) during a reproductive event usually give extensive parental care. • Devote much of their energy budget to these activities, sometimes at the expense of their own health. • Humans, chimps, kangaroos, pandas, etc. • The offspring of these species are relatively helpless at birth and need to develop before they mature

Low Fecundity (plants)

Plants with low fecundity produce few energy-rich seeds (such as coconuts and chestnuts) with each having a good chance to germinate into a new organism.

High Fecundity (plants)

Plants with high fecundity usually have many small, energy-poor seeds (like orchids) that have a relatively poor chance of surviving