Topic 3: Species Interactions, Communities and Ecosystems

Ecological niche

• Habitat or the specific area an organism inhabits

• The role or function of an organism or species in an ecosystem

• Interrelationship of a species with all the biotic and abiotic variables affecting it

What is a niche NOT

BUT

• Definition of a niche is not a location

  • Habitat is a place

• A niche is the conditions and resources needed to survive – these exist together in some places

Niche definition

Niche of a species is a multidimensional hyperspace, containing conditions and resources that allow the species to survive

Abiotic variables for each realm

Freshwater - small stones, big stones etc,

Environmental gradients

• Elevation

• Cover

• Aspect

• Solar radiation

• Temperature

Begon et al 2006 environmental gradient example

From drier areas to wetter areas, he counted the number of stems present as a percentage of the total number of stems

What determines where a species can live?

Abiotic

• Soils

• Temperature

• Water

• Shelter

But also:

• Food

• Competitors

• Predators

• Parasites

Niches are multidimensional

Ecological niches are multidimensional

• Abiotic and biotic factors layer to present niches

• Species evolve, adapt and compete to occupy niches

• when water deeper, flamingos are evolved to take advantage of this niche whereas ducks can duck and can catch food at the bottom

Summary of what contributes to the multidimensionality of ecological niches

Fundamental niche

We think of a niche as a multidimensional space. That space contains the conditions and resources a species needs to survive

A Fundamental Niche = anywhere those conditions are available (where a species could live)

A Realised Niche

A Realised Niche is smaller (where a species actually

lives)

Why realised niches are smaller than fundamental niches

‒ Competition, predation, parasitism

• in this case, the blue one might be out competing the brown one here so the brown one’s realised niche is smaller

‒ Dispersal limitations

• maybe that brown one might only be able to disperse to those upper levels

‒ Disturbances

‒ Stochasticity

• regular wave action or storms that reduce the realised niche for that species

What is a life history?

Patterns of survival and reproductive events across an organism’s lifetime

Life history of a butterfly

Life history trade offs

Throughout their lives, these animals have to make compromises to maximise their success with reproduction and lifespan throughout their lives

• one penguin spends all its energy on one egg while the other produces two smaller eggs with smaller resources

What does r represent? (population models)

The intrinsic rate of increase in a population (growth rate)

What does K represent (think about logistic growth curves)?

The carrying capacity of a population

r and K selected species comparison (mice vs elephants)

elephants’ reproduction timing is later bc they know they have that longer life

• bigger animals tend to have lower reproductive rates

Continuum - which animals might be more K vs r selected

r selected species can ‘boom’ and ‘bust’

• African locusts – an r-selected species

• Populations boom with good environmental conditions (abundant food)

• The life history strategy booms possible

• Females mature early, can lay 100 eggs at a time, and have a short lifespan

• 2-5 generations per year

• 10 fold increase in numbers possible from one generation to the next

K species more stable but can fluctuate

Fluctuations can occur in K species for biotic and abiotic reasons

• E.g. first crash in moose population due to high predation by wolves

• Second major crash due to harsh winter and food limitation 

Survivorship Curves

• Show survival patterns across age

• Plot proportion surviving at each age

• Reveal when mortality is highest

• Three classic patterns: Type I, II and III

• Linked to species' life-history strategies

There should be a log scale though - cannot have just percentages

Survivorship table

Key aspects of life histories

Number of reproductive events

Duration of a generation

Timing of reproductive events

2 types of ‘number of reproductive events’

Semelparous

Iteroparous

Semelparous

individuals breed once in their life

• Large investment in single reproductive event

• Often followed by death

• Examples: salmon, annual plants

Why choose semelparity?

• Conditions favour one large effort

• When adult survival is low enough (relative to juvenile survival), evolution should abandon withholding resources for a future reproduction and instead favour semelparity

  • basically short life span animals potentially

Iteroparous

individuals (potentially) breed multiple times in their life

• Reproduce multiple times during lifetime

• Investment spread across reproductive events

• Survival allows future reproduction

• Examples: marine turtles, kangaroos, humans, Eucalyptus trees

Two types of ‘duration of a generation’

Annuals

Perennials

Annuals

one generation per year (all lifespan into one year)

Perennials

one generation over several years

Summary of niches, r- and K-selected species, semelparity vs iteroparity and annual vs perennial

• Fundamental and realised niches differ

• r- and K-selected species differ in life-history traits

• Semelparous species reproduce once; iteroparous species

reproduce repeatedly

• Annual species reproduce within one year; perennial species

reproduce over multiple years

What is predation

This is a form of species interaction where one species eats another species

Can also include:

• Herbivory

• Parasitism – Lecture 27

Different types of species interactions

What do predators need to do?

Predators need to:

• Detect prey

• Locate prey

• Approach prey

• Capture prey

• Handle prey

What are the adaptations predators have to do these things?

• Sharp teeth

• Claws

• Talons

• Venom

• Sticky webs

• Powerful jaws

Types of predator

Specialists or generalists

• there are always trade offs (some things are advantageous vs disadvantageous)

Specialists

• Focus on particular prey

• Highly adapted to those prey

• Efficient at exploiting them

• Often have specialised hunting adaptations

eg. anteaters

Generalists

• Eat many prey types

• Have flexible diets

• Can switch between prey

• Can exploit changing food supplies

eg. dingoes

3 different strategies used to capture prey

a. crocodile

b. blue dasher (flying insect)

c. lion

Ambush Predation

• “Sit-and-wait” predators

• Heightened visual, chemical or tactile senses to detect prey

• Rapid movement of predator is key

• Most effective with high density prey

• Where prey low density – lures can be used (eg. angler fish using glowing bacteria)

Ballistic Interception

• Initially observe prey

• AND predict future prey location

• Escape by prey depends on:

• Local habitat

• Prey behaviour

How prey can avoid ballistic interception

Prey actually waits for snake to get closer…

• Possibilities other prey will distract snake

  • “Close quarters effect” increases angle of adjustment

  • Frog often waits until after the snake initiates a strike to begin its jump

Pursuit Predation

• Predator visual and auditory camouflage favoured

• High-speed locomotion of both predator and prey favoured

• Faster speed and acceleration improve fitness

Some more details abt relative size and speed of pursuit predators

How do prey escape from pursuit predation

Pursuit predation:

• Turning Gambit (Howland 1974)

• smaller animals can turn faster?

the recent study in image found that it might be more related to neural networks rather than size

Cooperation

Predators might also pool together and cooperate in order to increase hunting success

EG

• Wolves

• African Wild Dogs

• Lions

• Dolphins

• Orcas

Cooperation Pros

• Increased hunting success

• Efficient energy expenditure

• Resource and territory protection

• Enhanced safety

• Social learning and care

Cooperation Cons

• Shared rations

• Social conflict and dominance

• Increased visibility

• Cheating and free-riding

Prey strategies

Strategies prey use to avoid predation:

• Avoiding detection

• Avoiding capture

• Physical defences

• Chemical defences

• Warning signals

• Mimicry systems

• Behavioural mechanisms

Avoiding detection

• Match the environment

• Break up body outline

• Remain motionless

• Reduce detection

Avoiding capture

• Speed

• Agility

• Erratic movement

• Flight

• Burrowing

• Swimming

Physical defences

• Spines

• Shells

• Armour

convergent evolution example here

Chemical defences

• Toxins

• Venom

• Bad taste

Warning signals - Aposematism

Defence strategy where animals use bright colours, sounds or smells to warn predators they are harmful or unpalatable

Two types of mimicry

Batesian mimicry

Müllerian mimicry

Batesian mimicry

Harmless species resembles a defended/harmful species.

Müllerian mimicry

Multiple defended species share the same warning signals.

• eg. black and yellow stripes on wasps and bees

Behavioural mechanisms

Group living

Warning signals

Group living pros

• More eyes detect predators

• Dilution of individual risk

• Confusion of predators

• Collective defence

2 theories of why animals prefer group living

Dilution effect

Selfish Herd

Dilution effect

The probability of any one individual’s dying is diluted by the presence of others

Selfish herd

Individuals in a large group attempt to adjust their position by moving to the centre of the group because predators may be more likely to attack the outside 

Cons of Group Living

• More conspicuous (easier to spot for predators)

• Higher competition

Warning signals

The deer flashes it’s tail to indicate danger is coming

The wallabies make a stomping sound

Auditory signalling - just screeching lol

Naivity and learned behaviours

• “Naïve” prey may lack experience with predators

• Predators learn which prey are vulnerable

• Successful attacks reinforce predator behaviour

• Predation can shape behaviour over time

• E.g. island species - mainland species bc they are around foxes etc. spent more time acknowledging the scent of these predators while island species ignored it

Fiddler crabs example

Fiddler Crabs shelter in burrows to avoid predators but

• Lost time foraging (might not be able to find food)

• Lost reproductive opportunities (might not be visible to females)

Parasitism

“Parasites are predators that eat prey in units of less than one”

“Tolerable parasites are those that have evolved to ensure their own survival and reproduction but at the same time with minimum pain and cost to the host.”

Edward O. Wilson

Characteristics of parasites

Approximately 40% of all animals are parasites!

Parasites are:

• Smaller than their host

• Live on or in the host

• Usually don’t kill the host (but can)

• Hosts can recover from parasites

• Parasites habitats are alive, and can

• Grow

• Mount defences against parasites

• Evolve

• Move

Organisms that can be parasites

Can be:

• Protozoans

• Bacteria

• Animals

• Fungi

• Plants

Parasites - diversity

Super divers

• Important part of global biodiversity

• Parasitism is the most common consumer strategy among organisms

Trends across parasite diversity

Parasite diversity also:

◦ Poorly studied, grossly underestimated (Linnean shortfall)

◦ Newer species have fewer hosts

◦ Newer species have smaller distributions

Orange is what we currently know abt and blue is the ones that probs exist that we don’t know abt

Parasitism is costly as well

Types of parasites

microparasites

macroparasites

Microparasites

• Usually microscopic

• Multiply within host

• Often reproduce rapidly

• Individual parasites difficult to count

• Often cause infections rather than infestations

• e.g. bacteria, protozoa

Macroparasites

• Relatively large parasites

• Usually do not multiply rapidly within host

• Often present as individual parasites

• May live on or inside hosts

• Often have complex life cycles

• e.g. helminths, nematodes, tapeworms

Different techniques of transmission

How does a parasite (or the next generation) reach the next host?

• Direct contact

• Food

• Water

• Vectors

• Predation

• Sexual transmission

• Environmental stages

Parasite Manipulation

Ophiocordyceps unilateralis:

• Locally specialised parasite of arboreal Carpenter ants.

• Ant infecting Ophiocordyceps are known to make hosts climb down to a height of 25cm and bite onto vegetation before killing them.

Toxoplasmosis (example of parasite manipulation)

Toxoplasmosis in mice causes a characteristic "fatal attraction" phenomenon, removing their innate fear of cat odours and drawing them closer to predators

2 types of transmission

Definitive host (in Toxoplasmosis this is the cat)

Intermediate host

Definitive host

is an animal where a parasite grows into an adult and reproduces sexually (cat in toxoplasmosis)

Intermediate host

is an animal where the parasite lives as an immature larva and grows or reproduces asexually (mice, birds in toxoplasmosis)

3 types of life cycles for transmission

Direct or Monoxenic

Indirect of Heteroxenic

Direct or Monoxenic Life Cycles

feature one host

Indirect or Heteroxenic

life cycles involve multiple (often completely unrelated) organisms as hosts

• seems risky - trying to find a cow, ant and snail

What are the advantages of heteroxenic life cycles

• Parasites can safely grow, multiply, and store energy without killing the definitive host

• A single parasite can replicate into thousands or millions in intermediate host

• By splitting their life cycle adults and larvae do not compete for resources

• Using mobile hosts allows sedentary or aquatic parasites to cross geographic barriers and spread

• Many heteroxenic parasites align their life cycles perfectly with existing food chains

Parasites connect us to the world

What ‘One Health’ means

Why does ecology matter to human health?

• We can’t remove ourselves from ecological systems

We are linked by:

• Habitat change

• Wildlife contact

• Livestock production

• Vectors

• Water

• Food

Hendra Virus

• First detected in the Brisbane (Hendra) in 1994

  • 20 horses affected, 13 died

  • 2 people affected, 1 died

• Sporadic spill-overs from 1995 – 2005

• More frequent events since 2005

• Up to April 2026:

  • 90 outbreaks (63 QLD, 27 NSW)

  • 110 dead horses (incl. suspect cases)

• Seven affected people, four have died

• Fewer outbreaks since introduction of vaccine in 2012

Transmission pathway of Hendra Virus

Spillover events of Hendra Virus

Spillover events associated with food shortages and splintering of roosts into urban and agricultural areas

• Following El Nino peaks (green), we’ve had increase of spillover events bc drier conditions mean food shortages for flying foxes - this makes them stressed so they come closer in contact with humans to get food and then it spillovers into horses and then us humans

Nipah Virus

Malaria in the Amazon

• A 10% increase in deforestation leads to a 3.3% increase in malaria incidence

• The effect is larger in the interior and absent in outer states where little forest remains.

• This strong effect is only detectable after controlling for a feedback of malaria burden on forest loss

The influence of changes in environment on the risk

Climate change → vector distribution

Habitat change → wildlife contact

Urbanisation → new host interactions

Biodiversity change → alters disease transmission

Competition

Most typically considered the interaction of individuals that vie for a common resource that is in limited supply

• Organisms need resources in their daily life

• Resources are not unlimited

• Individuals may need the same resources

• Competition occurs when needs overlap

What do organisms compete for?

• Food

• Water

• Space

• Light

• Shelter

• Mates

2 types of competition

Intraspecific Competition

Interspecific Competition

Intraspecific Competition

• Between individuals of same species

• Same ecological requirements

• Particularly strong at high density

• Can reduce growth or reproduction

Interspecific Competition

• Between different species

• Resource requirements overlap

• Can affect population growth

• Can influence where species occur

Forms of competition