Population Distribution and Abundance

Case Study: Distribution of Kelp Forests

Areas with large numbers of urchins are called “urchin barrens” because they lack kelp forests.

Urchins feed on algae and can significantly reduce kelp populations, leading to ecological imbalances.

This was tested in the Aleutian Islands and along the Alaskan coast. It showed that urchins might determine where kelp forests are located.

Population

A group of individuals of the same species that live in a particular area and interact with one another.

Population Size

Number of individuals

Population Density

Number of individuals per unit area

Distribution

Geographic area where individuals of a species occur

Abundance

Number of individuals in a given area of a specific species or population.

Populations are _____. Distribution and abundance can change over time.

Dynamic

Aspen Groves: One Tree or Many?

Represents multiple different genetic individuals, each established from a seed. However, it is possible to be reproduced asexually from the root buds of a single genetic individual.

Genet

Reproductive units sharing a single identical genotype

Ramet

If members of a genet are independent physiologically, each member is known as a ramet

Absolute Population Size

Actual population abundance

Relative Population Size

Number of individuals in one time period or place relative the number in another

Area-Based Counts

The number of individuals in a given area or volume are counted.

This is used to estimate absolute population sizes of organisms that are sessile (plants) or can move only short distances during the time it takes to count the individuals in a quadrat.

Also for more mobile organisms, such as in aerial surveys…can help provide estimates of relative population sizes.

Mark-Recapture

Estimates the absolute population size of mobile organisms, they are also used to obtain data on the survival or movement of individuals.

Formula: Marked/ Pop = Recaptured/Captured

Distance methods: Line transects

In distance methods, an observe measures the distances of individuals seen from a line or a point; these distances are then converted into estimates of the number of individuals per unit of area

Scarce yellow sally stonefly

This image highlights a fascinating breakthrough in conservation biology: the use of environmental DNA (eDNA) to find species that experts feared were lost forever.

In this specific case, researchers used eDNA to rediscover the Scarce yellow sally stonefly (Isogenus nubecula) in Wales, a species that hadn't been seen in the UK since 1995.

Dispersion

Spatial arrangement of individuals in a population

Types of Dispersion

Regular: individuals are evenly spaced

Random: individuals are randomly spaced

Clumped: most common pattern in nature, where individuals aggregate in patches

Habitat Fragmentation

the breaking of large, continuous ecosystems into smaller, isolated patches, primarily caused by human activities like road construction, agriculture, and urban development

Ex: Heathlands in England

Species Distribution Model

computer-based tools that predict a species' spatial distribution by linking known occurrences with environmental data like temperature and land cover

Geographic range

includes all the areas a species occupies during all life stages

Case-study: Sex-based conservation plans

Many migratory land birds overwinter in separate place

(i.e., sexual segregation)

Only 8% of conservation plans for North American

landbirds account for sexual segregation, with biases

for male-dominated habitat

In Golden-winged Warblers, females lost twice

as much habitat as males from 2000

Habitat

natural environment of an organism

Habitat suitability depends on a combination of abiotic and

biotic factors

Abiotic: moisture, temperature, pH, sunlight, nutrients, etc.

Biotic: food, predation, competition, herbivory, parasites

Habitat Suitability: Cresote bush vs Saguaro cactus

The geographic distribution of creosote bush (Larrea tridentata) is much larger than that of saguaro cactus (Carnegiea gigantea).

How does food availability influence habitat suitability

Seychlls warbler

Birds with high-quality territories live longer and produce more young

High quality sites are aggregated toward one end of the island

Dispersion of individuals is clumped as a result

Some species can become invasive and affect distributions

In Australia, an introduced cactus became a pest species

A moth that feeds on cactus was then released

Distribution and abundance of the cactus was been greatly reduced

Cane beetles and invasive species

Released in Queensland to control cane beetles (did not work)

Toads spread southwards and across the northwest of Australia

Harmed Australian wildlife A

Abiotic and biotic features can help determine distribution and abundance

Semiblanus balanoides’ range is restricted by temperature

Competition from other species precludes it from some areas with suitable temperatures

Some species depend on disturbance

Fire frequency can change community composition

Human suppression of fire allows non-fire tolerant species to out compete fire adapted species

Pitch pines (Pinus rigida) in the NJ Pine Barrens:

• Serotinous cones only open and shed seeds after fire

• Fire clears undergrowth allowing for the pine saplings to dominate

Continental Drift

Alfred Russell Wallace (1860) observed very different animal species on the Philippines and New Guinea, even though they are very close

together.

Relictual distributions

Occur when the range of a formerly widespread species contracts or is fragmented

Ex: Pine Barrens Tree Frogs