Ben's lectures

Question 1

Hutchinson 1957

Answer 1

How tolerances and requirements interact to determine conditions and resources needed by an organism to practice its way of life. An n-dimensional hypervolume can be mathematically represented on a graph, thinking of many dimensions affecting where an organism can live. An organism will inhabit areas within hypervolume providing accessibility and that there is no preclusion of other organisms (competition, predation).

Question 2

Fundamental + realised niches

Answer 2

Fundamental niche is where it could live based on the environmental conditions, a realised niche is where it does live given all other factors.

Question 3

Competition

Answer 3

An interaction between species, brought about by a shared requirement for a resource, leading to a reduction in the survivorship, growth and/or reproduction of a least some of the competing individuals concerned.

Question 4

Interference competition

Answer 4

Where species interact directly to prevent the other from accessing resources.

Question 5

Lokta-Volterra models

Answer 5

Dominance controlled communities- one is a stronger interspecific competitor than the other, so the other species is driven to extinction

Founder controlled communities- both are strong interspecific competitors, and weak intraspecific competitors. One species dominates, depends on the initial density.

Coexistence- if they are both weak interspecific, and strong intraspecific competitors.

Question 6

Principle of allocation

Answer 6

Limitations to resources define trade-offs; reproductive episodes vs fecundity per episode, gametes vs energy reserves, no- of young vs energy spent protecting them. Can be separated into k and r selected species.

Question 7

Recruitment and settlement

Answer 7

Recruitment- the survival of offspring to a defined stage, like the exploited stock (of fisheries) or the no. of individuals entering adult population (ecology/fisheries). Basically, the number of individuals joining a population. It’s important to know what drives recruitment and any variation before since recruitment variability can be high.

Settlement- the point at which the organism takes up a benthic or demersal existence.

Question 8

Larval strategies

Answer 8

Planktonic- depend on plankton food, longer pelagic duration (PLD). PLD influences dispersal of individuals.
Lecithotrophic- have they own food from their yolk, shorter PLD.

Non-planktonic- direct development, no larval stage.

Question 9

Larval mortality

Answer 9

Mortality through the egg, larval and juvenile stages is huge
-Transport processes
-Environmental stress (temp, salinity)
-Starvation (not much energy)
-Predation (very underdeveloped, small and vulnerable)

Question 10

Types of mortality

Answer 10

Humans are a type 1 mortality where we tend to die at the end of our lives, turtles and amphibians are more type 2 where they die throughout the life history, and fish are mostly type 3 where not many survive past the larval and juvenile stages.

Question 11

Cushing 1975

Answer 11

Match-mismatch hypothesis. Where the recruitment is determined by the seasonal overlap between the production of larvae and prey resources. Its suggests the timing of larval production in relation to the timing of the production cycle will determine larval survival. This is just one of the possibilities given.

Question 12

Larval crab transport (Mid-Atlantic bight to South-Atlantic Bight).

Answer 12

-Wind-surface currents directly depend on season, buoyancy driven currents depend on estuarine outflow, and tidal currents depend on local influence.
-Winter has an onshore Ekman transport and a strong southward coastal current, summer has an offshore Ekman transport and a weaker southward coastal current.

-Crabs mate in the estuaries in the summer, inseminated females release eggs at the estuary mouth on nocturnal high tide, they drift south and then offshore and north.
-They are transported onshore by episodic southward winds in late summer and autumn.
-This shows how much larvae are affected by abiotic factors only.

Question 13

Presettlement vs postsettlement

Answer 13

-In the blackspot gobi species there was settlement without predators, and then the apparent settlement with predation was very low. Leaving no recruitment.

-In bridled gobi’s, the settlement was less with predation and less recruitment, but changes were minimal.

Question 14

Density-dependence

Answer 14

When biological rates are dependent on population density. Density dependence is thought to occur after settlement due to resource bottlenecks. Compensatory density-dependence is when there is an inverse relationship between density and population growth rate.

Population growth rate = birth rate – death rate.

-Time of maturity, fecundity and survival rates would all affect the birth rate, resulting from competition and predation (affecting resources, survival). Often occur in post-settlement due to resource bottlenecks.

Question 15

yellowtail damselfish case study

Answer 15

-They live planktonically and then they will settle on coral heads
-Relationship between the density of juvenile damselfish and the proportion lost over a 72-hour period, with exposure to predators or complete protection from them.
-Also found that most predation was found at night, so there was competition between damselfish for the safe locations within the coral.
-As they increased the density of the damselfish, the predation increased since more fish were pushed to the edges of the coral = density-dependent mortality.

Question 16

Functional responses of predators to prey

Answer 16

Type 1 is where predators eat a constant proportion of the prey until a given point.

Type 2 is the impact of predators gradually reaches the plateau.

Type 3 is like 2 but predators eat an increasing proportion of prey at low densities.

An aggregative response is when there are more prey in a certain area, then predators all crowd around there since they know they will get fed. As more prey enter the environment, the predators become better at catching prey. And if there are even more prey then predators relax a bit since there will be enough for everyone for a period of time.

Question 17

Competition vs predation

Answer 17

Competition: reduced survival at high density (death), reduced fecundity at high density (birth).

Predation: type 3 functional response (death), aggregative response (death.

-All reduce population growth rate at high population sizes = population stability.

Question 18

density-mediated interactions

Answer 18

If there is an interaction where one species is eaten, this means there will be fewer of those prey making it easier for the predators.

Question 19

Density-mediated indirect interaction case studies

Answer 19

-Predation where Pisaster (starfish) limits down shore extension of Mytilus (stalked barnacles). When they removed the starfish, there were more stalked barnacles on the lower shore, however they retreated up shore again when the starfish were reintroduced.

-Herbivorous fish and urchins consume around 100% of daily algal production, despite an increase in production during the summer (grazing also increases). Reducing the density of the grazers, the whole ecosystem would shift from a coral dominated state to an algal dominated state. The grazers can be affected by humans or disease, which indirectly affects the coral/algae by grazing variation.

-Trophic cascades also indirectly affect species. If humans hunt orcas, there are more seals, so there are less sea urchins and more kelp. And yet if there are less seals due to higher populations of orcas, sea urchin populations boom (urchin barrens) and there is a loss of kelp.

Question 20

Trophic cascades

Answer 20

Occur when there is a low diversity of strong interactions (keystone species), and top-down control (what happens at the top affects the lower levels).
Most systems have weaker and diverse interactions making them more complicated.

Question 21

Trait-mediated interactions

Answer 21

Predators change both the populations and behaviour of their prey. Some examples below. Predators often create landscapes of fear.

-Sol fish grow much faster when predators are absent, whereas when predators they eat less so they also grow less. A trade-off between growth and survival.

-Dog whelks consume barnacles, crabs consume dog whelks and also change their feeding behaviour. The crab reduces the density of dogwhelks (consumptive interaction), which means more barnacles survive (density-mediated). When there are crabs, whelks feed differently, and barnacle mortality also varies (trait-mediated).

Question 22

Complex interactions example

Answer 22

Fucoids dominate on the shore, Littorina grazing lowers diversity by selecting competitive inferior ephemerals. Ephemerals dominate in pools and diversity is highest at intermediate Littorina grazing (intermediate-disturbance hypothesis).

Question 23

Recruitment mechanisms

Answer 23

Hjort 1914 critical period hypothesis
-Recruitment was determined by survival during a critical period (early life) and offshore dispersal to unfavourable areas.
-Zonation was driven by larval availability, settlement behaviour and mortality.
-Main paradigm: high input = strong biotic interactions, low input = weak biotic interactions.

Question 24

Sediment properties

Answer 24

Texture involves the individual and bulk characteristics of the particles making up the sediment.
-No.1 properties = size, shape, orientation, nature
-No.2 properties = influenced by No.1 properties. Porosity, permeability, penetrability, surface area.

Question 25

Horizontal exposure gradient

Answer 25

Variation in wave fetch between shores, within shores. -Gradients of water motion- edge waves, tides, wind, infragravity waves -Sediment transport means water velocity control the distribution of sediment, since the bigger particles will be dropped first. Flow determines the deposition of sediment. When the speed of the current slows, the sediments drop and settle. -When water flows across a sediment it declines due to friction, to the point where the water in contact with the sediment can stop entirely. -Particles can move through suspension, saltation, sliding, rolling.

Question 26

Beach characteristics

Answer 26

Complex interplay between wave climate, beach slope and particle properties. Key drivers are particle size and wave energy, and tidal range.

Question 27

Swash + backwash

Answer 27

When waves ‘plane’ on the beach. The swash deposits all of the sand and the backwash smooths it out again. When particles are coarse, the swash is more powerful (dominant) than the backwash. Swash often creates accretion and a steep beach face.

Question 28

Dimensional fall velocity (DFV)

Answer 28

Describes the sediment mobility, the state of the beach. -If you have a low wave period, you have less deposition -If you have a high sediment fall velocity, then you have less tendency for the sediment to move around -This can determine different types of beaches

Question 29

Reflective beach

Answer 29

Low wave energy, large particles. Surging breaker waves, steep slope.

Question 30

Dissipative beach

Answer 30

Big waves, but small particles, flat beach. -These beach types have consequences for particle movement, water filtration, circulation/dispersal and water flow.

Question 31

Horizontal exposure gradient

Answer 31

Horizontal exposure gradient and how they change with beaches with different particle sizes. Dissipative beaches tend to have a higher biomass, whereas reflective beaches tend to have larger particles and larger organisms but fewer of them. Reflective beaches tend to be more stressful with harsher waves which is not great for supporting life.

Question 32

Swash exclusion hypothesis: McLaclan 1995

Answer 32

Swash climate is most benign on dissipative beaches until becomes harsher and more species are excluded towards reflective conditions, until, in the most extreme reflective conditions no intertidal species occur.

Question 33

Biotic factors mediate response to swash climate

Answer 33

-They use swash to move up and down the beach to exploit different intertidal zones -They can also burrow to avoid the harsh swash, and to protect them from fish or birds. They also move around to avoid each other in the species. -Grain size, temperature, and predators all affect whether they can burrow or not. -Zonation is dynamic, affected feeding, predation and standing.

Question 34

Sandy beach predation

Answer 34

Birds, fish, crabs are the major predators, which tend to reduce diversity (competition is less intense). Crabs cant burrow because of their bivalves.

Question 35

Sediment destabilizers: overall effects on habitat

Answer 35

-Increasing water = seabed exchange of sediment (deposition, suspension) -Changing sediment particle composition (agglutination fractionation) -Changing sediment particle composition (diffusive mixing, bringing fine material to surface, coarse material downwards) -Loosening and fluidising the sediment (ploughing, free burrowing, creating feeding voids) -Changing the sediment chemistry and microbial metabolism (pumping overlying water into the sediment, digging air chambers) -Facilitating drainage of sediment at low tide -Increasing seabed, water flux of nutrients/metabolites -Altering near-bed hydrodynamics (topography, ventilation currents) Negative effects- could create avoidance, mortality Positive effects- oxygenation, habitat creation

Question 36

Sediment stabilisation

Answer 36

-Seagrass, mangroves which bind the sediment together and change the environment -Lanice conchilega is a worm which can act as a stabiliser in high density sediment (act as stabilising rods) -Epipelic algae exude EPS to migrate through sediment -Episammic algae which sticks grains together with EPS -Filamentous cyanobacteria form a network of sticky EPS threads.

Question 37

Overall effects on habitat

Answer 37

stable sediment + fine sediment -Consequences for porosity, permeability, penetrability, surface area -Therefore, also physical and chemical conditions

Question 38

Eugene Odum systems approach

Answer 38

Compared the flow of water over an oyster reef, compared to the flow of a city (food, waste, heat). Surmised they work very similarly in terms of energy requirement.

Question 39

Trophodynamics

Answer 39

Trophe is Greek for nourishment, measured in carbon currency. -Trophic structure and energy flow through food webs (energy = carbon-based molecules). How energy moves between systems.

Question 40

Flow of energy

Answer 40

The ultimate energy source is the sun, fuels heat. Then there is a primary producer that fixes the energy from the sun and turns it into carbon-based molecules which are more accessible. It is passed up through consumers and then lost as heat through respiration. Energy may move to other systems, or end up at detritus which feeds a whole different food web. But is mostly lost through respiration.

Question 41

Gross primary productivity (GPP)

Answer 41

how much carbon is initially fixed in a system

Question 41

Biomass

Answer 41

How much living matter there is in a given unit area or volume, gC m-2

Question 41

Productivity

Answer 41

the rate at which the biomass is produced gC m-2 y-1

Question 42

Net primary productivity

Answer 42

how much of the initial carbon fixing is used as living biomatter, GPP- respiration

Question 42

secondary productivity

Answer 42

the rate at which biomass is produced by consumers, by feeding on other organisms

Question 43

ecosystem productivity

Answer 43

can measure it by taxonomic group, or the ecosystem over all. GPP – sum of all respiration = ecosystem level productivity. Basically, how much is fixed – how much is lost by respiration. If its positive it means the ecosystem is a source of energy or a sink.

Question 44

Primary producers in pelagic ecosystems

Answer 44

-Energy comes from sun but is restricted to the surface -Photosynthesis controlled by nutrients and light -As light declines, so does photosynthesis -Rate of respiration remains constant with depth -Compensation depth is where plants can’t grow so more energy is being used than produced, they can’t photosynthesise but they continue to respire.

Question 44

Primary production in shallow, coastal waters

Answer 44

-High nutrients due to upwelling or riverine input -Light can be limiting -As you move away from the coast the nutrient levels declines -The compensation depth gets deeper, the water gets clearer -Sediment and algae makes the euphotic zone shallower at shore -Somewhat away from the coast is a peak euphotic zone, with depth and nutrients.

Question 45

Secondary production -> Efficiency of tropic transfer

Answer 45

TE = CE x AE x PE TE = transfer energy CE = consumption efficiency AE = assimilation efficiency PE = production efficiency

Question 46

energy between trophic levels

Answer 46

Consumption, assimilation and production efficiency define how much energy is transferred between trophic levels. Roughly 10% usually. There can be a big variation between the percentage of trophic-level transfer efficiencies.

Question 47

Biomass ratios

Answer 47

Productivity per unit of biomass. -or the biomass achieved for a given level of productivity, often called turnover. -In the ocean, primary producers’ biomass is quite low but they can turnover quite fast. -But for a given level of biomass, aquatic producers tend to be more productive and produce more per unit of biomass.

Question 48

Meiofauna

Answer 48

small, microscopic organisms -biomass production tends to decrease with size -production and biomass ratios for them are very high -to do with the organism size and metabolic rate, they are less productive but dont use as much

Question 49

Allochthonous vs autochthonous production

Answer 49

Marine- in situ production, few external inputs in the open ocean (autochthonous). Woodland- allochthonous production since the system is heavily affected by external factors

Question 50

Forms of energy between ecosystems

Answer 50

-Dead organic material (detritus, carrion, DOM, POM) -Living organic material (advection of plankton, larval settlement, movement of adults). Energy can move over very vast distances (birds feeding on horseshoe crab eggs).

Question 51

Routes for macrophyte litter

Answer 51

-may feed microorganisms, or consumers. -may break down = organic matter

Question 52

Energetic links between systems

Answer 52

In macrophyte dominated systems (marshes, seagrass beds, kelp beds)- often don’t export DOM or POM. It fuels depositional, unvegetated habitats (like sand flats in western wadden sea, there is enough to feed so a lot is imported).

Question 53

Energy in mudflats

Answer 53

Example of where imports can occur: -Most of energy comes from bacteria in sediment -Which is feeding on the organic matter which is important -Which feeds the rest of the food chain -There is some import from algae and suspension feeders

Question 54

energy in rocky shores

Answer 54

exporters and importers -Can be exposed (epifauna like barnacles and mussels, epibionts, so most of energy comes in as phytoplankton through filter feeding, or some grazing on algae), semi-exposed = whichever they can get to) or sheltered (fucoid production feeding snails).

Question 55

energy in sandy beaches

Answer 55

-Not many macrophytes (algae, seagrass) -Some carrion (dead animals) -Dissolved organic matter (DOM) -Some plants and insects from land -Diatoms in the sand (Episammic diatoms attach to sand, Epipelic diatoms migrate through the sand), and surf zone diatoms (suspended). -Consumers include filter feeders, surf zone zooplankton, and scavengers. Also some meiofauna (nematode, gastrotrich, turbellarian, oligochaetes, copepods etc. with a base of bacteria). They almost act as a huge natural filter, since they feed on bacteria and are very productive which remineralises the nutrients.

Question 56

Energy in Western Cape, SA

Answer 56

-The biggest energy input is seaweed which feeds insects and amphipods in the drift line. -Not much intertidal fauna -Bacteria is important in forming the base of the food chain -Ends with higher predators like birds and carnivorous amphipods.

Question 57

Energy in Eastern Cape, SA

Answer 57

-Dissipative beach, big beach system -Very well-developed circulation systems with currents and wave energy -Many brown patches with diatoms and algae in rip-circulation -This means biomass accumulates in the surf zone -Diatoms form a mucus coat in the current when they can’t photosynthesise anymore, then in the morning they shed their mucus coat and attach to bubbles to bring them to the surface again !!! -Very high biomass production ratios, 90% production through mucus, exudates and cell division. -This concentrates in the foam and gives a food source to benthic or pelagic filter feeders -There are three systems just here; the macrofauna, interstitial fauna (consumes around 20%) and the microbial loop (very important, consume bulk of primary production).

Question 58

Plaice

Answer 58

Flat fish species, live on sand, commercially important. They spawn in winter with pelagic eggs, which drift through the water column and enter a settlement stage. Normally on sandy, moderately exposed shores. Juveniles in sandy beaches. By the time they leave (after a summer of growth), they are palm sized.

Question 59

Plaice mortality

Answer 59

Throughout egg, larval and juvenile stage there is a lot. Due to transport, environmental stressors, starvation and predation. These determine how many individuals contribute to the adult populations.

Question 60

Plaice recruitment variation

Answer 60

Not much variation compared to bass, there are a few years with many recruitments but tends to be stable. Stabilisation usually occurs in juvenile stages. There tends to be increased variability when food is limited. The larval stage shapes recruitment numbers (most variation), and then there is already less variation by the juvenile stage.

Question 61

Density dependence

Answer 61

When biological rates are dependent on population. Often through biotic interactions like competition (increasing mortality, decreasing growth rate).

Question 62

Compensatory density dependence

Answer 62

When pop growth rate declines at higher densities, there is negative feedback. -In years of low densities there are higher pop. growth rates which stabilises it again. - A decrease in population growth rates can be driven by an increase in mortality rates in early life.

Question 63

Plaice competition

Answer 63

-Compete with themselves (intra-specific) -Crangon shrimp (inter-specific), share the same food as plaice, and they also predate on younger plaice (selective mortality since they only choose small ones). Link between growth and mortality, the faster you grow, the faster you leave the vulnerable period where you are vulnerable to the shrimp.

Question 64

Mechanisms of density dependence

Answer 64

-Recourse bottleneck in the early juvenile phase (starvation) -Resource competition = compensatory density dependence in individual growth -Negative size-selective predation by shrimp results in compensatory density dependent mortality

Question 65

Optimal food condition hypothesis

Answer 65

-Some hypothesis suggested there would be maximum growth, some say it would have been limited. -Factors controlling growth aren’t just optimal food conditions, it also depends on location, and at which point food limitation has the worst affect. -They were measuring the average size throughout a season, not specific individuals.

Question 65

Ben's growth measure

Answer 65

He developed a tool to measure growth, to get many estimates to cover large areas. -You can measure growth through muscle (level of RNA in tissue to predict how fast they are growing). RNA and growth rate are temperature dependent. G = f(RNA) in field. You can indirectly infer the growth rate from the RNA and temperature. This will also give you the variation. Then you are left with a model to predict growth rates (RNA index).

Question 66

Growth variation

Answer 66

Temperature, prey conditions, inter/intra-specific competitor density. -Also includes seasonal dynamics.

Question 67

Ben's conclusion to Optimal Food Hypothesis

Answer 67

-Needs to be put in a temporal context -Maximum growth studies were taken at the beginning of the summer -Minimum growth was found towards the end of the summer -Ben explained patterns through a temporal decline in growth rate, and that temperature and food competition in unrelated.