Ben's lectures Flashcards
Hutchinson 1957
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).
Fundamental + realised niches
Fundamental niche is where it could live based on the environmental conditions, a realised niche is where it does live given all the other factors.
Competition
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.
Interference competition
Where species interact directly to prevent the other from accessing resources.
Lokta-Volterra models
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 wear interspecific, and strong intraspecific competitors.
Principle of allocation
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.
Recruitment and settlement
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.
Larval strategies
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.
Larval mortality
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)
Types of mortality
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.
Cushing 1975
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.
Larval crab transport (Mid-Atlantic bight to South-Atlantic Bight).
-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.
Presettlement vs postsettlement
-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.
Density-dependence
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.
yellowtail damselfish case study
-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.
Functional responses of predators to prey
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 areas, 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.
Competition vs predation
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.
density-mediated interactions
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.
Density-mediated indirect interaction case studies
-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.
Trophic cascades
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.
Trait-mediated interactions
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 consumer 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 fed differently, and barnacle mortality also varied (trait-mediated).
Complex interactions example
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).
Recruitment mechanisms
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.
Sediment properties
Texture involves the individual and bulk characteristics of the particles making up the sediment.
-No.1 properties = size, shape, orientation, nature
-No.2 properties = influences by No.1 properties. Porosity, permeability, penetrability, surface area.
Horizontal exposure gradient
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.
Beach characteristics
Complex interplay between wave climate, beach slope and particle properties.
Key drivers are particle size and wave energy, and tidal range.
Swash + backwash
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.
Dimensional fall velocity (DFV)
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
Reflective beach
Low wave energy, large particles. Surging breaker waves, steep slope.
Dissipative beach
Big waves, but small particles, flat beach.
-These beach types have consequences for particle movement, water filtration, circulation/dispersal and water flow.
Horizontal exposure gradient
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.
Swash exclusion hypothesis: McLaclan 1995
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.
Biotic factors mediate response to swash climate
-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.
Sandy beach predation
Birds, fish, crabs are the major predators, which tend to reduce diversity (competition is less intense). Crabs cant burrow because of their bivalves.
Sediment destabilizers: overall effects on habitat
-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
Sediment stabilisation
-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.
Overall effects on habitat
stable sediment + fine sediment
-Consequences for porosity, permeability, penetrability, surface area
-Therefore, also physical and chemical conditions
Eugene Odum systems approach
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.
Trophodynamics
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.
Flow of energy
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.
Gross primary productivity (GPP)
how much carbon is initially fixed in a system
Biomass
How much living matter there is in a given unit area or volume, gC m-2
Productivity
the rate at which the biomass is produced gC m-2 y-1
Net primary productivity
how much of the initial carbon fixing is used as living biomatter, GPP- respiration
secondary productivity
the rate at which biomass is produced by consumers, by feeding on other organisms
ecosystem productivity
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.
Primary producers in pelagic ecosystems
-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.
Primary production in shallow, coastal waters
-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.
Secondary production -> Efficiency of tropic transfer
TE = CE x AE x PE
TE = transfer energy
CE = consumption efficiency
AE = assimilation efficiency
PE = production efficiency
energy between trophic levels
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 that are transferred though.
Biomass ratios
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.
Meiofauna
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 done use as much
Allochthonous vs autochthonous production
Marine- in situ production, few external inputs in the open ocean (autochthonous).
Woodland- allochthonous production since the system is heavily affected by external factors
Forms of energy between ecosystems
-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).
Routes for macrophyte litter
-may feed microorganisms, or consumers.
-may break down = organic matter
Energetic links between systems
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).
Energy in mudflats
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
energy in rocky shores
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 (mostly a mix between expose and sheltered, whichever they can get to) or sheltered (fucoid production feeding snails).
energy in sandy beaches
-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.
Energy in Western Cape, SA
-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.
Energy in Eastern Cape, SA
-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).
Plaice
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.
Plaice mortality
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.
Plaice recruitment variation
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.
Density dependence
When biological rates are dependent on population. Often through biotic interactions like competition (increasing mortality, decreasing growth rate).
Compensatory density dependence
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.
Plaice competition
-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.
Mechanisms of density dependence
-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
Optimal food condition hypothesis
-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.
Ben’s growth measure
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).
Growth variation
Temperature, prey conditions, inter/intra-specific competitor density.
-Also includes seasonal dynamics.
Ben’s conclusion to Optimal Food Hypothesis
-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.
