Science

1. Population Ecology

2. Ecologists often define a
population as a group of
individuals of a single species
inhabiting a specific area .
Populations are characterized by
the number of individuals and their
density, as well as additional
characteristics such as age
distributions, growth rates,
distribution, and abundance.
Population Distribution and
abudance

3. Distribution limits
The physical environment limits the geographic distribution of a
species, as organisms can only compensate so much for
environmental variation. Climate can also indirectly influence
species distributions via food production and the incidence of
parasites, pathogens, and competitors.
Examples of distribution limits include:
-Kangaroo Distributions and Climate: There is a close relationship between
climate and the distribution of the three largest kangaroo species in
Australia .
- Tiger Beetle of Cold Climates: The tiger beetle (Cicindela longilabris) lives at
higher latitudes and elevations than most other species in North America .
-Distributions of Plants Along a Moisture-Temperature Gradient: Encelia
species distributions correspond to variations in temperature and
precipitation .
-Distributions of Barnacles along an Intertidal Exposure Gradient: Barnacles
show distinctive patterns of zonation within the intertidal zone . Chthamalus
stellatus is restricted to upper levels, while Balanus balanoides are limited to
middle and lower levels .

4. Distribution patterns on
small scale
On small scales, the distribution of individuals can be random, uniform (regularly spaced), or clumped.
- Random: Equal chance of being anywhere . It assumes a uniform distribution of resources .
-Regular: Uniformly spaced, with exclusive use of areas where individuals avoid one another .
-Clumped: Unequal chance of being anywhere, due to mutual attraction between individuals or patchy
resource distribution .
Examples of distribution patterns on small scales include:
-Distributions of Tropical Bee Colonies: Aggressive bee colonies tend to show regular distributions,
while non-aggressive species show random or clumped distributions.
Distributions of Desert Shrubs: Young desert shrubs are often clumped due to seeds germinating at
safe sites, limited seed dispersal, or asexual reproduction . As the shrubs grow, competition can lead
to a reduction in clumping and the eventual creation of regular distributions.

5. Distribution of individuals on
large scale
At a continental scale, bird populations across North America
show clumped distributions. Clumped patterns occur in species
with widespread distributions . Tree species also showed a highly
clumped distribution along moisture gradients, with densities
decreasing substantially toward the edges of their distribution.

6. organism Size and population
density
Generally, population density declines with increasing organism
size . The population density of herbivorous mammals decreases
with increased body size . Aquatic invertebrates tend to have
higher population densities than terrestrial invertebrates of
similar size, and mammals tend to have higher population
densities than birds of similar size. Plant population density also
decreases with increasing plant size. Tree seedlings can live at
very high densities, but as the trees grow, density declines
progressively until mature trees are at low densities.

7. Geographic Ecology

8. Scientists seek to understand why certain species are found in specific locations and what
factors influence their survival and dispersal. Climate, landforms, and resource availability
play crucial roles in determining where species can thrive.
A well-known pattern within geographic ecology is the latitudinal biodiversity gradient, which
describes how biodiversity is typically higher in tropical regions and decreases toward the
poles.

9. area, isolation and species richness
Area: In ecology, the area refers to the physical size or extent of a habitat or ecosystem. The size of an
area can influence the number and diversity of species it supports.
Isolation: Isolation in ecological terms refers to how separated or isolated a particular habitat is from
other similar habitats.
Species Richness: Species richness refers to the number of different species present in a given area or
ecosystem.
Sampling Area: The sampling area refers to the specific portion of an ecosystem or habitat that researchers
choose to study in order to estimate or measure the characteristics of the whole environment (such as
species diversity, abundance, etc.).
Number of Species: The number of species refers to the count of different species within a given sampling
area. This is a simple measure of species diversity.
species richness, which is the total number of different species in a sampling area without accounting for
how many individuals of each species are present.
Sampling area and numbers of species

10. Island area and species richness
Island Area: Island area refers to the physical size of an island, or any isolated habitat, such as a forest
patch or a mountain.
Species Richness: Species richness refers to the number of different species present in a particular
area, such as an island.
Island Isolation: Island isolation refers to how far an island is from other land masses or nearby islands.
Species Richness: Species richness refers to the number of different species present on an island or in a
given area.
Island Isolation and species richness

11. species turnover on island
Species turnover on islands refers to the continuous process of species replacement due to
immigration, extinction, and sometimes speciation.
Experimental island biogeography involves controlled scientific studies to observe species colonization,
extinction, and turnover in island-like environments.
experimental island biogeography
colonization of new islands by plant
When a new island forms—whether through volcanic activity (e.g., Hawaii, Surtsey) or other geological
processes—plants must establish themselves from scratch.
manipulating island area
Scientists manipulate island area in experiments to study how habitat size affects species richness, colonization,
and extinction.

12. island biogeography update
These advancements underscore the dynamic nature of island biogeography, reflecting a more
comprehensive approach that integrates ecological, genetic, and anthropogenic perspectives to
inform both theoretical models and conservation efforts.
Latitudinal gradients in species richness refer to the well-documented pattern where biodiversity increases
toward the equator and decreases toward the poles.
latitudinal gradients in species richness
area and latitudinal gradients in species richness
The latitudinal diversity gradient (LDG) and the species-area relationship (SAR) are two fundamental
patterns in biogeography that help explain global biodiversity trends.
historical and regional influence exceptional pattern of diversity
Biodiversity is shaped not only by contemporary ecological factors but also by historical and regional influences
that have contributed to exceptional patterns of diversity.

13. investigating the evidence and sample size revisited
Larger sample sizes reduce random variation and improve the accuracy of biodiversity estimates.
Latitudinal gradients in species richness refer to the well-documented pattern where biodiversity increases
toward the equator and decreases toward the poles.
latitudinal gradients in species richness
area and latitudinal gradients in species richness
The latitudinal diversity gradient (LDG) and the species-area relationship (SAR) are two fundamental
patterns in biogeography that help explain global biodiversity trends.
historical and regional influence exceptional pattern of diversity
Biodiversity is shaped not only by contemporary ecological factors but also by historical and regional influences
that have contributed to exceptional patterns of diversity.