Niches and competition/Measuring Biodiversity

Conservation of species requires a

community perspective

consider interactions:

• predator and prey

• herbivory

• parasite and host

• mutualism

• competition

Why does biomass decline at higher trophic levels? 

energy loss at each transfer step going from producers to primary consumers, secondary, tertiary, and quaternary 

Chemoautotrophs 

some autotrophs don’t use sunlight 

use inorganic compounds like sulfur, Iron, or Nitrogen as energy sources 

deep sea vents

Nitrogen fixing by bacteria

iron oxidizing by bacteria occur naturally in water containing high levels of iron

Organisms use most energy in

solely staying alive rather than building biomass

Mobile links

move nutrients and biomass

move seeds and spores

EX: dung beetle, seed dispersal, whale fall, salmon migration, birds

Matter Nutrients can be

recycled through the environment but energy cannot

Epiphytes

nutrient storages in rain forest canopy

4x biomass of leaves in tress

tress access nutrients by sending roots from trunks to epiphyte areas

Measuring Biodiversity: Genetic diversity

time and resource intensive to measure accurately

focus on individual species

can’t do this for fossils

of greatest utility in conservation and management of rare species

Biodiversity refers to

how many and what kinds of species are present, usually in association with conservation biology or extinctions

Species diversity refers to

a measure that incorporates number of species and relative abundance

Species richness

the number of species in an area; often the
only information available,
depends on baseline taxonomic data

Species evenness

relative abundance of species

Community composition 

varies between location

alpha, beta, gamma diversity 

any diversity index can be used to calculate these values 

Alpha diversity

biodiversity in a single location or habitat

Beta diversity

variation in community composition between locations or habitats usually calculated as bet=gamma/mean of alpha

Gamm diversity

total biodiversity on a landscape scale (many
habitats)

Percentage cover 

the proportion of each quadrat
occupied by the species.

usually used for plants but common
for corals, sponges, barnacles etc

Population density

the number
of individuals per unit of area

Species frequency 

the proportion of quadrats with the
species in it.

Camera traps and other passive sampling methods

Presence absence of
species
Population size (if you
can tell individuals
apart)
Location and time
Activity patterns
When are animals active
and moving?
Age, sex, reproductive
status

Mark recapture works for animals that move around

Trap, mark, and release

Then wait a while and trap again

Count how many are marked

Populations size= number in 1st sample x number in 2nd sample/ number in 2nd sample previously marked

Species abundance tends to have a Lognormal Distribution

Plot log10 of species abundance (x-axis) vs. number of
species (y-axis) (Fig. 16.3 and 16.4)

In many communities, distribution is “normal” (bell-
shaped) when x-axis is plotted on log scale

How do you know when you’ve done
enough sampling?

sample size is important

as much you can for time and money

Sample size is important

The common species show up in
even small samples

Great sampling
effort to capture the
rare species

This is why new
species are still being
discovered

Speices- Area

curves tell us when you have sampled large enough area 

Rank Abundance Curves are a useful way of displaying biodiversity data 

graphically depict patterns
of species diversity, species
richness and species
evenness
• X-axis: species’ ranks
(1=most abundant)
• Y-axis: Relative abundance
(proportion of total
individuals)
• Slope of line indicates
evenness
Steep slope: Low
evenness
Shallow slope: High
evenness
Note that the abundance is on a log scale.

hen both species richness and
species evenness increase, there
is by definition an increase in

biodiversity

Simpson’s diversity index (D)

measure of biodiversity that takes into
account richness and evenness.
A high value for D is ‘good’ and means the
habitat is diverse, species rich, and able to
withstand some environmental impact.

gives more weight to common or dominant
species.

What is a problem with that?

can underestimate biodiversity in habitats where a few species are very abundant and many others are rare. This means rare species have little influence on the final value of the index, even though they may be ecologically important or at risk of extinction

Mutualism

Interactions between individuals of different species that benefit both partners

Facultative mutualism

• occurs when a species can live
  without its mutualistic partner.

• This relationship is mutually
  beneficial, but not mandatory for
  survival

Obligate mutualism

• occurs when a species is
  dependent on a mutualistic
  relationship.

• This relationship is necessary for
  the survival or reproduction one or both species

Plants and fungi often form mutualistic relationships

Mycorhizae (root-fungus)
- Fungi associated with plant
roots: Plant receives minerals and
other nutrients gathered by the
fungus
- Fungal hyphae increase
surface area of the root
system: Fungi can decompose organic
matter and extract nutrients

- Fungus receives sugars
produced by the plant: Plants can use photosynthesis
(fungi cannot)

Mutualism and the endosymbiosis hypothesis

• Eukaryotic life probably originated as a mutualism between organelles (chloroplasts and mitochondria in
  cells)

• Structure and genetics are very similar to bacteria and cyanobacteria

Infraspecific competition

occurs between members of the same species

density dependent regulator of a population

When populations get very
large, this will slow population growth, or even reduce the population

Interspecific competition 

• Competition
  between species

• Species with similar
  niches are often
  grouped into Guilds

• Guilds often have
  closely linked
  population dynamics

Competition is also categorized

according to the mechanism by which it occurs

Interference competition

occurs when an individual directly prevents
another from obtaining resources.
- For example: a fish that aggressively
chases away other fish to monopolize
a nesting site

Exploitative competition

occurs when individuals deplete resources
that would otherwise be available to
others; in this case there is no direct
agonistic interaction.
- For example: the depletion of nutrients
by an individual algal cell reduces
nutrient availability to others algal cells

Competition can limit an

animals niche

Niche partitioning

• Two niches could theoretically be adjacent, and
  there would be no competition between the species
  • Niche overlap – when two niches overlap there will
  be intense competition
  • There will be Niche partitioning– the superior competitor will eliminate its competition in the overlapping zone, and the niche overlap will be
  divided between the two species

• but the two species may still coexist side by side if
  they have enough non-overlapping niche

There are tradeoffs between being a

generalist or a specialist

Generalists

sacrifice efficiency for the ability to use a wide range of resources.
superior to specialists if resources are
somewhat undependable

Specialists

can often occupy difficult or harsh
environments that generalists cannot. They take advantage of open niches and are superior to generalists if resources are dependent

Competitive exclusion and the niche

• If there is too much
  niche overlap, one
  species will. Drive the
  other out

• It may not go
  completely extinct,
  but it will be pushed
  to the edge, where it
  may have a specialist
  advantage

Habitat

The characteristics of the type of environment where an organism normally lives, including climate and biotic community

describes an anima’s env

Niche of a species consists of

Its role in the ecosystem
(herbivore, carnivore,
producer etc)
- Its tolerance limits (e.g. soil
pH, humidity)

- Its requirements for
shelter, nesting sites etc
etc, all varying through it’s
life cycle

describes the animal evolutionary strategy for survival in that env

Shannon’s diversity index 

Higher is better.
-  assumes all species are represented in a
sample and that they are randomly
sampled.
- Can you point out any problems in
these assumptions?

it’s unlikely that all species in a community are represented in a sample — some may be too rare or difficult to detect. This means the Shannon Index can underestimate true diversity if sampling is incomplete. Additionally, the assumption that species are randomly sampled is often unrealistic, since sampling methods, habitat accessibility, or observer bias can cause non-random sampling, leading to skewed results.