Species interactions in the real world (guppies!!)

Question 1

When does lotka volterra fail? Give an example using algae

Answer 1

LV is fine for genetically diverse prey eg. snowshoe hair and lynx - it predicts predators ¼ of a cycle behind prey and that is what you see.

Studies with algae (Clonal prey) don’t do what we expect – lag is ½ a cycle NOT ¼ of a cycle
o Found that algae are clonal – come in 2 types
- ‘clumpers’ - clumps of cells are too large for the predator to eat
- ‘non-clumpers’ – exist as single cells, predators can eat

In the absence of predators, single cells have an advantage over the clumped cells (more SA so can take up more nutrients)

Predator starts to eat single cells, decline in these and increase in other clone, predators start to die out, cycle repeats

The fitness of ‘clumper’ and ‘non-clumper’ prey varies with predator numbers

o Can think of this as an evolutionary response
o Prey gene frequencies fluctuate with predator numbers
o Shows how the real world is more complicated than simple LV models

Question 2

What are guppies a good example of?

Answer 2

Nice example of…

• the complexity of species interactions
• evolution as species interactions change

Question 3

What are guppies like above the waterfall

(low predation)

Answer 3

Life history differences

• Later sexual maturity
• Lower investment of resources in reproduction
• Fewer and larger offspring
• Slow life history (live slow live long)

Demography
- high density populations

Behaviour
- don’t hang around in shoals

Morphology

• less streamlined
• males are more brightly coloured

Swimming performance
- slower

Diet
- feed on algae and bacteria

Question 4

What are guppies like below the waterfall

high predation

Answer 4

Life history differences

• Earlier sexual maturity
• Greater investment of resources in reproduction
• More and smaller offspring.
• Fast life history (live fast die young)

Demography
- low density populations

Behaviour
- hang around in shoals

Morphology

• more streamlined
• more drab males

Swimming performance
- faster

Diet
- feed on invertebrates

Question 5

Why are guppies a really good (model!!) system to study eco-evolutionary dynamics?

Answer 5

• Short generation times of 3-4 months

in order to see eco-evo dynamics in a few years you need organisms that are not v old when they reproduce and don’t live for v long

• They naturally differ (life history, morphology) above and below waterfalls (diff ecological environments) - this can be experimentally manipulated!!
• you can make observations in natural streams, semi-natural systems and in the lab - one of the few ecological systems that permits use of all aspects of the scientific method

Question 6

name the things that differ between guppies

Answer 6

• size
• life history
• reproductive strategy

Question 7

what separates the high and low predation zones

Answer 7

barrier waterfall

Question 8

How can you experimentally manipulate mortality?

Answer 8

• Transplant guppies from high-predation localities into sites from which they and their predators had previously been excluded by natural waterfalls, thus lowering mortality rates
• Introducing predators into low-predation sites, thus increasing mortality rates.

Question 9

name the things that differ between guppies

Answer 9

• life history
• demography
• behaviour
• morphology
• swimming performance
• died

Question 10

Describe methods for tracking and monitoring guppies during experiments

Answer 10

Anaesthetise & put coloured dots on that allows recognise them

• Weigh them
• take one of their scales for genetic analysis

Question 11

How can you experimentally manipulate mortality rates?

Answer 11

• Take guppies from high-predation streams and place in low-predation streams thus lowering mortality rates
• Introducing predators into low-predation sites, thus increasing mortality rates.

In each case, leave to evolve for many generations

Question 12

Describe methods for tracking and monitoring guppies

How do these differ in the different experimental environments used?

Answer 12

In the natural streams of Trinidad - Mark-recapture methods!!

• Anaesthetise & put coloured dots on that allows recognise them
• Weigh them
• take one of their scales for genetic analysis

Artificial streams in the field (Mesocosm experiments)

• you can manipulate fish community structure and population sizes
• can see how fish compete with one another
• put canopy on top to mimic rainforest around

Lab experiments in Wytham

Question 13

Why does high predation alter guppies?

Answer 13

o They die from being eaten by predators
o Pop size below K
o Reduced numbers = less density dependence = less intraspecific comp
o This means they can afford to have a very high metabolic rate and grow fast
o Selection for different life histories, size, etc

Question 14

Why does low predation alter guppies?

Answer 14

o There is basically nothing external killing them (apart from killifish)
o Pop size v high
o Pop density v high = high intraspecific comp for food
o Instead of being limited by predators, are instead limited by how much food there is!
o less food means they can’t have a high BMR so can’t grow fast

• This means the guppies die of starvation – this contributes to the change in reproductive strategy we see
• Also they change their diet, eating algae and bacteria. This means their microbiomes change and the ecology of the environment changes!! (eco-evo feedback)

o Selection for different life histories, size, etc

Question 15

What’s eco-evolutionary feedback? Provide an example

Answer 15

change ecology -> this will affect evolution (cause a genetic change in a species) -> see how the evolution FEEDS BACK and affects the ecology/ environment

ie. genetic change generates a change in the biotic environment an organism experiences
- results in change in selection pressure in the focal species
- that in turn alters the direction or strength of evolution

They could provide a figure that incorporates

• genes, phenotypes and populations, with a feedback from the population to genes level of the figure - KEY THAT GENES ARE CONNECTED TO ECOSYSTEMS VIA PHENOTYPES
• The figure could also include community and ecosystem boxes as these are parts of the biotic environment

EXAMPLE = guppies in Trinidad.

Question 16

How many generations does it take to see these changes in guppy populations?

Answer 16

10-30 generations (1 gen = 3-4 months)

Question 17

How do we know the changes in guppies are genetic, and not just due to phenotypic plasticity?

Common garden experiments

Answer 17

• Take fish from Low Predation stream and from High Predation stream
• Grow them in the lab in the exact same environment and leave for 2 gens (separate tanks!)
• Compare life histories of the two streams
• Find that differences between streams remain

Over 2 gens, differences persist so must be genetic differences that had been evolved, too short to evolve again!)

• We can pin down which genes change over many gens between high and low predator populations

Question 18

Which direction can you move guppies in?

Why only one direction?

Answer 18

Move high predation guppies to low predation environments

You can’t put low pred in high pred stream as they will go extinct

Question 19

Is guppy evolution repeatable?

Answer 19

There are different genetic routes to maximising fitness!

• Think of evolution as mountain range, with fittest at peak (best phenotype for that environment)
• Different streams have diff adaptive landscapes with ‘different mountain ranges’
• There may be 2 peaks – evolution may find 2 routes to top of mountain (diff genetic changes)
• The ‘route’ over the adaptive landscape differs between environments (canopy type and how much light gets to stream)

BUT low predation guppies always evolve from high predation guppies when released from predation

Question 20

Describe the eco-evolutionary feedback seen in guppies

How can you test this?

Answer 20

Genetic changes alter ecological environment

Guppies affect algal growth differently in different streams, so the streams look different!

Why?
High predation guppies
o Are more efficient at consuming invertebrate prey
o Prey selectivity on higher quality prey

Low predation guppies
o High intraspecific competition for food because of high densities of guppies
o This means they have expanded the food they eat to include algae
o Guppies scour all rocks and take algae and bacteria off

Experiments
• Can do experiments to see how different types of guppies affect stream
• . Weak electric field to scare guppies away in one stream

Question 21

Using a well-studied example, describe what happens when a prey species is released from predation.

Answer 21

When guppies are freed from predation, we see an initial increase in numbers.

Instead of being predation limited, the population now becomes limited by competition for food.

Over between 10 and 20 generations, this leads to myriad changes in the morphology, behaviour and life history of the guppies.

For example, the life history slows down, with size and age at first reproduction increasing, generation time increasing, average adult body size increasing, litter size decreasing, offspring mass decreasing, life expectancy increasing.

The diet changes too, to individuals feeding on algae and bacteria at high density compared to invertebrates at low density.

Fish swarm less at high density, and are more diurnal at high density too. These changes are evolutionary in flavour, as revealed by common garden experiments.

Question 22

Explain, with examples, how ecology can influence evolution and vice versa (combined EJMG & TC)

Answer 22

o First define ecology – the study of population or community dynamics will suffice.
o Next define evolution – change in allele frequencies would be an appropriate answer.

If ecological change alters selection pressures leading to evolution, and evolution alters the impact the ecological environment by influencing the population or community dynamics, you have eco-evolutionary dynamics.

Guppy example: Population density increases Food resources decline Population reaches carrying capacity
Diet changes, shifting from consisting nearly entirely from invertebrates to include bacteria and algae
Selection pressure changes on life history and phenotypic traits
Over thirty or so generations, life history slows, with increases in age and size at maturity, a decrease in litter size, and an increase in offspring size
Swimming speed slows
Morphology changes with fish become less streamlined
Behaviour changes, with fish schooling less Poster child example of density-dependent selection and evolution

Other lecture examples

• The change in prevalence of a dark colour morph in the peppered moth was as a result of pollution causing trees to become a darker colour. This made the moth easier to spot by predators. This ecological process then led to evolutionary change, such that the dark colour morph became more prevalent
• In the case of the saiga antelope, it is evolved to have a “boom-bust” life history that makes it well adapted to life in the harsh environment of the steppe, where adverse weather can cause mortality but them fast, intense, high cost reproduction allows them to bounce back. However, this also makes them vulnerable to disease and to poaching. Poaching reduces numbers so that when some mortality event happens they may not be able to bounce back. New diseases which strike at the time of maximum stress (birth) can cause massive population crashes. This was seen in 2015 in Kazakhstan.