Predator Prey Relationships

Primary things animals care about

food, reproduction, not being eaten

Apex predator

species that occupy the top trophic position in a community

Mesopredator

encompasses any mid-ranking predator in a food web, regardless of size or taxonomy, that occupies trophic positions below apex predators

Predators are at least…

secondary consumers or above

Globally, top predators are…

declining

Botton-up control

Fewer primary consumers create a lack of food for upper trophic levels, leading to die-offs

Top-down control

Predation pressure on upper trophic levels releases mesopredators which decrease populations of lower trophic levels

Three reasons the effects of overfishing are hard to identify

1)lack of baseline data prior to disappearance of large number of predators

2)importance of top- up processes & resource limitation in many places

3)prevalence of omnivory, opportunism, that weaken interactions between trophic level

First phase of overfishing

Large species are fished and disappear

Second phase of overfishing

smaller fish that have high market and cultural value are fished and disappear

Third phase of overfishing

Small fish that are easy to catch are fished and disappear

Fourth phase of overfishing

Only undesirable fish are left

Non-consumptive effects of predation

Limiting movement, changes in phenotype, changes in offspring, changes in foraging behaviour

Consumptive effects of predation

population control

5 ways fish sense their environment

hearing, olfaction, lateral line, vision, taste

physical changes in prey when predators are present

smaller eyes, wider bodies, smaller offspring, longer fins,

Early ontogeny (early development) behaviour characteristics

pelagic dispersal behaviour, orientation & habitat detection, settlement

Recruitment behaviour characteristics

post-settlement habitat selection & ontogenetic migration, feeding, migration, homing

Juvenile phase

competition for resources, prey detection/foraging success/food selectivity, predator detection/recognition/avoidance

Adult phase

habitat use, spawning migration, timing of spawning & spawning behaviour

Between 2024 and 2025 what was the increase in ppm of CO2

2.54 ppm CO2 (428.59 in 2024 and 431.13 in 2025)

What does environmental change do to organisms

puts them in evolutionary novel conditions

Main mechanisms that impact animal behaviour

Ocean acidification and temperature rise

Ocean acidification and temperature increase impact what aspects of marine organisms

Physiology, resources, environmental cues, other species

What is the one aspect that only ocean Ph affects in marine organisms

Neurology

What happens to fish in high CO2 environments

impact olfactory system making them less able to find suitable habitat, locate food, and avoid predators

Why do acidic oceans impact behaviour of marine organisms

GABA receptors act like a brake on electrical circuits in the brain (inhibitory neurotransmitter slows the over-stimulation of neurons)

• GABA binds to a receptor, opening a channel that lets - charged chloride ions flow into the neuron

• Under acidified conditions, chloride ions flow out of the neuron instead of into it

• The neuronal brake becomes an accelerator leading to behavioural change

How does CO2 and low PH impact odour molecules and fish behaviour

CO2 changes the H bonds of the odour molecule causing odour molecules to no longer attach to olfactory receptors in the same way which causes an altered detection of odours leading to different response from neurons and different behaviour

The ability of species to cope with EC depends on…

Plasticity (Past environment, present environment, evolutionary history, individual performance, population performance, future evolution)

characteristics of acclimation

Physiological, morphological, or behavioural plasticity

Rapid phenotypic responses (individual level)

Characteristics of genetic adaptation

Phenotypic change driven by genetic selection that is inherited from one generation to the next (evolutionary level)

Main threats facing marine environments today

ocean acidification, temperature increase, pollution, overfishing