Freshwater Ecology Flashcards
1
Q
Describe the different types of wetlands, their hydrology,
dominant vegetation and important ecosystem properties or
functions.
A
Wetland Hydrology:
Gains:
* precipitation, surface and
groundwater
* tidal/coastal – bidirectional flow
Losses:
* Evapotranspiration
relatively more important
* Directional flow – losses
when rivers flow through
Hydrologic regime is the most important
abiotic factor determining wetland ecology
Wetlands degrading overtime due to agriculture.
High biological diversity of both aquatic and
terrestrial organisms
Ephemeral (drying up) or extreme abiotic
conditions
Often with locally adapted biodiversity as a result
2
Q
Discuss how variation in discharge and velocity of a river
system can lead to habitat and biological diversity.
A
In-channel features, such as woody debris and submerged vegetation, can also give rise to significant variability in water velocity and depth within a reach of river. This spatial variability can be important for maintaining habitat diversity and biodiversity, including different life stages within individual species.
3
Q
Discuss how self-organisation can lead to the characteristics
of a flowing water feature and affect the landscape it is
flowing through.
A
A system is self-organizing if it acquires a spatial, temporal, or functional structure without specific interference from the outside. By “specific” we mean that the structure or functioning is not impressed on the system but that the system is acted upon from the outside in a non-specific fashion.
4
Q
Describe the transport of materials by rivers and discuss
their role in the global carbon cycle.
A
Atmospheric carbon dioxide dissolves in rainwater, making it slightly acidic. This dissolves rocks, allowing the carbon to flow down rivers and into the ocean, deposited in new rocks — usually calcum carbonate. This moves carbon from the atmosphere into the lithosphere.
river ecosystem metabolism consumes organic carbon derived from terrestrial ecosystems, which produces CO2 emitted into the atmosphere
5
Q
Discuss the processes that lead to boreal kettle lakes being
one of the most common lake types globally – and most
important in a climate change context
A
Kettles form when a block of stagnant ice (a serac) detaches from the glacier. Eventually, it becomes wholly or partially buried in sediment and slowly melts, leaving behind a pit. In many cases, water begins fills the depression and forms a pond or lake—a kettle.
The massive Lakes act like heat sinks that moderate the temperatures of the surrounding land, cooling the summers and warming the winters. The lakes also act like giant humidifiers, increasing the moisture content of the air. In the winter, this moisture contributes to heavy snowfall known as “lake effect” snow.
6
Q
What are the main ways in which lakes are formed? (Tectonic and glacial,)
A
Tectonic activity
Lake origins – glacial activity
The Great Lakes (US / Canada)
Lake Superior, Michigan, Huron, Ontario & Erie
Michigan is the world’s largest freshwater lake by area
Formed during glacial retreat at end of last Ice Age
Retreating ice sheets exposed the basins they had carved into the land
Filled with meltwater
7
Q
how are volcanic lakes formed?
A
Crater lakes usually form through the accumulation of rain, snow and ice melt, and groundwater in volcanic craters. Crater lakes can contain fresh water or be warm and highly acidic from hydrothermal fluids.18 Apr 2023
Crater lakes form as the depression left behind following a volcanic eruption fills with
water. This may come from precipitation, groundwater, or melted ice. Its level rises
until an equilibrium is reached between the rates of incoming and outgoing water.
8
Q
Lake origins – damming
A
Beavers, landslides and reservoirs.
9
Q
Lake origins – ephemeral
A
Ephemeral means temporary
Many ponds are an example (dry up in hot weather)
Many other natural cavities that host freshwater life (treeholes, pitcher plants, tank bromeliads)
10
Q
What is an ecosystem?
A
All of the living things (organisms) and non-living things (abiotic factors) in a specific area
A single type of organism is a species
Every member of a species in one area is called a population
All of the populations in an area make up a community
The species found in an ecosystem are determined by both abiotic factors and other organisms
11
Q
What are the major abiotic factors influencing lake ecosystems? (Including details on solar radiation)
A
Solar radiation
Light penetration
Mixing and stratification
Almost all solar radiation completely absorbed in first metre of water column
Varies daily due to angle of sun
95% of incident radiation is transmitted when sun is high
Reflection increases when sun is lower in the sky
Reflected light cannot be used for photosynthesis
Algal production will vary both seasonally and daily due to solar radiation
12
Q
Light penetration details
A
Water clarity determines how deep light can reach
Dissolved organic matter can lead to brown colour in lakes, e.g. decomposed plants and animals, tannic & humic acids
Turbid water can result from suspended sediments
Surface run-off from soil also increases turbidity
Transparency often reflects abundance of phytoplankton
Clear lakes in winter, phytoplankton blooms in summer
Nutrient enrichment can also promote phytoplankton blooms
13
Q
Mixing & stratification
A
Temperature of water determines its density
Peak density is at 4 °C
Water is lighter at both higher & lower temps
Ice floats on liquid water
Bottom of lake will be last part to freeze in winter
This also leads to thermal stratification
Epilimnion is the warm top layer of stratified lake
Metalimnion or thermocline contains a temperature gradient
Hypolimnion is the cold bottom layer of a stratified lake
Stratification broken down by wind or convective overturn
Mixing affected by depth, size, shape, climate, topography, vegetation & inflow from streams
14
Q
Different types of mictic lakes.
A
Monomictic lakes only mix from top to bottom once a year, e.g. polar lakes mix during ice-free summer, ice-free temperate lakes may mix throughout winter
Dimictic lakes have two seasons of mixing (spring and autumn) and two seasons of stratification (summer and winter)
Polymictic lakes stratify and mix several times a year, e.g. tropical lakes
Meromictic lakes rarely mix from top to bottom
Amictic lakes are permanently covered in ice and never mix, e.g. Arctic, Antarctic, alpine regions
15
Q
Littoral zone – periphyton
A
Phytoplankton uncommon in littoral zone
Instead, microscopic algae live in biofilms attached to submerged surfaces
Most common on rocks and attached to macrophytes
Includes diatoms, green algae & cyanobacteria, but also detritus, polysaccharides & heterotrophic bacteria
16
Q
Limnetic zone
A
Open water zone where sunlight can penetrate
Low diversity, but high density of organisms
Concentration of phytoplankton is strongly related to concentration of phosphorus (Krebs 2009)
Nutrient status determines amount of primary production
17
Q
Littoral zone
A
Typically dominated by macrophytes and diverse animal life
Macrophytes can be emergent, floating, or submerged
18
Q
Limnetic zone – phytoplankton
A
Oligotrophic = nutrient poor, few phytoplankton, clear water
Eutrophic = nutrient rich, many phytoplankton, murky water
19
Q
Limnetic zone – zooplankton
A
Zooplankton grazers feed on phytoplankton in water column
Most common groups are:
Cladocera (Daphnia spp.)
Copepoda
Rotifera (wheel animals)
20
Q
Limnetic zone – rotifers
A
Small generalist filter feeders (<1 mm)
Consume bacteria, algae & protozoa in 0.5 – 18 μm range
Distinctive morphological features
Corona of cilia used in locomotion and food collection
Pharynx used to grind food
Most species are parthenogenic – huge reproductive potential
21
Q
Limnetic zone – defensive strategies in phytoplankton
A
Phytoplankton:
Thick cell walls to decrease digestibility
Spines to increase handling time
Large size to avoid some grazers
Colonial forms to increase overall size
Mucilaginous sheaths for movement
Toxins
22
Q
Profundal zone
A
No light, no algae and often low oxygen concentration
Dominated by bacteria and fungi
Animal life relies on organic matter sinking from the surface or on migration upwards to obtain food
Bloodworms (Chironomidae) are deposit-feeders in the muddy benthos, adapted to anoxic conditions
(2) Clams filter organic matter from water column & sediment
(3) Phantom midges (Chaoborus spp.) live in profundal zone during day and migrate to limnetic zone at night
23
Q
Seasonal changes in eutrophic lakes
A
Shifts in light:
low in winter
high in summer
Shifts in nutrient concentrations:
high in winter & spring
low in summer
Shifts in grazing pressure:
low in winter & spring
high in “clear-water phase”
low in early summer
high later in summer
24
Q
Eutrophic versus oligotrophic lakes
A
Oligotrophic lakes follow a different trajectory
Nutrients are too limited for a summer bloom
Zooplankton abundance is much greater (and later) as a result
25
Temperate versus tropical lakes
Tropical lakes have a lower magnitude of variability of incident light, water temperature, and nutrient availability
Also less seasonal variability, but more short-term (day-to-day and week-to-week) variability
26
What makes a river a river?
No official definition, but related to its size
Rivers can be categorised according to their order (Strahler number)
1st order streams have no other water flowing into them (source or spring-fed streams)
If two 1st order streams join, they become a 2nd order stream
If a smaller order stream joins a higher one, the new branch retains the higher number
1st – 3rd order are called headwater streams – they make up about 80% of the world’s waterways
4th – 6th order are medium streams or mid-reaches
7th – 12th order are generally considered rivers
27
The major biotic groups in lotic systems are:
Basal resources:
(a) algae (periphyton / biofilms / bryophytes / macrophytes) = green pathway
(b) dead organic matter (carrion / leaves / fine particles / dissolved material) = brown pathway
Microbes (e.g. bacteria, fungi)
Meiofauna (e.g. ciliates,
flagellates)
Macroinvertebrates
Fish
28
The 5 functional feeding groups in a river ecosystem.
Shredders = Break up leaves and other coarse particulate organic matter (CPOM)
Collector gatherers = Collect periphyton & fine particulate organic matter (FPOM) from the benthos
Filter feeders = Filter FPOM and phytoplankton from the water column
Sometimes called collector filterers and pooled with collector gatherers as “collectors”
Scrapers / grazers = Scrape encrusting periphyton off the surface of rocks
Predators = Feed on other invertebrates and are typically the biggest organisms
29
Biofilms
Phytoplankton are only found in the largest and deepest lower reaches of big rivers
Most algal resources occur in the form of periphyton on stones, i.e. biofilms
Diatoms, green algae, and cyanobacteria dominate
Crustose, prostrate, gelatinous forms can only be accessed by scrapers
Stalked or filamentous forms are mainly accessed by collector gatherers
30
Abiotic factors change along rivers
Moving from headwaters to larger rivers:
Slope and substrate size decrease
Channel width, depth & discharge increase
General transition from erosion through transport to deposition
This has consequences for resources and their consumers
31
The River Continuum Concept (Headwaters)
Headwaters:
Channel is narrow, steep
Water is fast flowing
Riparian vegetation is typically dominant
Canopy cover limits light
Major energy input is allochthonous ((of a deposit or formation) having originated at a distance from its present position.)
Dominated by leaves & CPOM
Major invertebrate groups are shredders & collectors
32
The River Continuum Concept mid-reaches
Channel widens, allowing more light through
Temperature increases
Algal production now greatest (autochthonous)
Increasing importance of FPOM transported from CPOM broken down upstream
Dominant inverts are scrapers & collectors (including filter feeders)
33
The River Continuum Concept (Large rivers)
Widening channel & decreasing flow
Macrophytes become more abundant
Phytoplankton can even be present
FPOM is the main source of energy
Dominant inverts are collectors, particularly filter feeders
34
Serial Discontinuity Concept
Most rivers affected by human activities
Dams create a discontinuity in the river
Gradual downstream transition of RCC is disrupted
Movement of animals is impeded
Organic matter transported by river is deposited behind dam
Availability of food downstream is reduced
35
Hyporheic Corridor Concept 1/3
Water does not just flow downstream
It flows vertically & laterally in the hyporheic zone
Hypo = below; rheos = flow
Hyporheic zone is the space beneath & beside the stream bed
There is mixing of oxygen-rich surface water with nutrient-rich groundwater in this zone
36
Hyporheic Corridor Concept 2/3
Important component of floodplain dynamics
Links secondary channels to main river
Provides exchange of nutrients & organisms with wetlands
Water flows more slowly in hyporheic zone, so it is a valuable source of carbon and dissolved nutrients from groundwater
Also provides an important shelter / habitat for organisms
37
Hyporheic Corridor Concept 3/3
Salmon lay their eggs under gravel – cooled by groundwater
Alevins use the hyporheic zone for shelter during development
Hyporheic zone is also a refuge during drought or other stress
Groundwater flow persists through gravel
Crayfish and inverts can burrow down to reach this.
38
Lotic vs lentic dispersal
Freshwater habitats are either lentic (standing) or lotic (running). On average, lotic habitats are more stable and predictable over space and time than lentic habitats. Therefore, lentic habitats should favour the evolution of higher dispersal propensity which ensures population survival of lentic species.
39
Summary for lentic and lotic dispersal
Dispersal is more than movement
* Determines genetic structure of populations
* Contributes to Landscape scale diversity
* Can be part of metapopulation
* “Fish” populations are heterogeneous movers
* Connectance is key at larger spatiotemporal
scales
* Species interactions play a large role in successful
dispersal and colonisation
40
What is alpha, beta and gamma diversity?
Alpha diversity is the species diversity present within each ecosystem on a landscape. Beta diversity is represented by the species diversity between any two communities. Gamma diversity of is the species diversity across the entire landscape, taken as one unit. Scale is absolutely critical in ecological studies.
41
Summary of
Dispersal in Communities
Dispersal a key process in colonisation and
community assembly
* Invasion sequence could lead to multiple
stable states
* Results relatively consistent between field and
lab studies
* Dispersal of predator and prey both important
* Connectance , and time, governs dispersal
42
sympatric and allopatric speciation
In allopatric speciation, groups from an ancestral population evolve into separate species due to a period of geographical separation. In sympatric speciation, groups from the same ancestral population evolve into separate species without any geographical separation.
43
Patterns of interaction strengths in food webs
Stability of coupled strong & weak interactions demonstrated by McCann et al. (1998)
Consumer feeds its preferred resource close to extinction (strong interaction)
It can switch to its less preferred resource(s), so it still has food (weak interaction)
This allows the population size of its preferred resource to recover
This type of module is extremely common in food webs
Facilitates stable consumer-resource dynamics through time
44
Food webs like games of Jenga!
Changes in species identity and strength and composition of trophic links
Rewiring of ecological networks compared to a game of Jenga (DeRuiter 2005)
A Jenga structure is constantly changing with addition & deletion of stones
Stability depends on contribution of ingoing & outgoing stones to underlying structure
45
Sampling of streams for food webs
Electrofishing to quantify fish (e.g. 3 passes of a 50 m reach)
Surber sampling to quantify macroinvertebrate community plus leaf litter, FPOM, etc.
Rock scrapes to quantify biofilm community
46
Sampling of lakes for food webs
Electrofishing / seine nets / gill nets / fyke nets for sampling fish
Tow net (or hand net) for sampling zooplankton
Van Dorn sampler for sampling phytoplankton
47
Quantifying food web structure
Stomach flushing (or dissection) of fish to quantify:
Which prey species they have been eating
How many of each prey they have been eating
Identifying stomach contents under the microscope
Prey items often heavily digested, difficult to identify
Potential to use DNA analysis to determine which prey have been consumed
48
What is a trophic cascade?
and different types
Trophic cascades result in inverse patterns in abundance or biomass across more than one trophic link in a food web (Pace et al. 1999)
Species-level cascade: occurs within a subset of the community – changes in predator numbers affect a subset of plant species
Community-level cascade: substantial alteration to distribution of biomass throughout an entire ecosystem (Polis et al. 2000)
First conceptualised as Green World Hypothesis (Hairston, Smith & Slobodkin 1960)
Carnivores suppress herbivores, thus indirectly allowing plants to grow
Introduced the concept of top-down forces and indirect effects shaping ecological communities.
49
Body size: why do we care?
Body size determines many aspects of an organism’s function in ecological systems
E.g. home range, ingestion rate, secondary production and nutrient turnover
Body size is also an important determinant of consumer-resource interactions
Aquatic systems in particular are highly size-structured
Metabolic rate has been shown to scale predictably with body size & temperature (Brown et al. 2004)
Changes in either or both of these properties will alter metabolic demand and the flow of energy through food webs
50
Impacts of warming: decreasing body size
Ectotherms rely on their environment to regulate their body temperature
Smaller ectotherms are better competitors for limited resources (Reuman et al. 2014)
For example, smaller diatoms have a larger surface to volume ratio and so can absorb more nutrients per unit biomass
In contrast, endotherms regulate their own body temperature
Smaller endotherms have proportionally larger surface area & thinner boundary layers
They can “dump” heat more effectively than larger organisms
Smaller size is favoured in warm environments
Bergmann’s rule: smaller species generally found in warmer regions
James’s rule: smaller-sized populations of the same species in warmer environments
Temperature-size rule: individuals will be smaller at a given age in warmer environments
51
Impacts of warming: loss of top predators
Trophic pyramids are extremely common in nature
Rule of thumb: only 10% of energy transferred to next highest trophic level
Top predators are most likely to suffer when energy demands increase throughout
52
Evidence for increased nutrient supply in algae
Nutrient cycling is higher in warmer streams (Demars et al. 2011)
Nitrogen fixation (by cyanobacteria) also increases with temperature (Welter et al. 2015)
There are more nutrients to fuel the greater production of algae at higher temperatures
53
Thermal performance curve
Thermal performance curve (TPC)
Some organisms may sit close to or at their thermal optimum
Increasing temperature leads to a decline in thermal performance
Organisms close to CTmin may have scope for increased performance
54
Trophic transfer efficiency 1/2
Sunlight is converted more efficiently into gross primary production as stream temperature increases
This may be related to increased nutrient cycling in warmer streams (Demars et al. 2011)
More nutrient resources available to fuel production
More resources at the base of the food web
These available resources are also converted more efficiently into invertebrate biomass
GPP to invertebrate transfer efficiency increases with stream temperature
Cold streams dominated by very selective grazers (Chironomidae)
Warm streams by more efficient grazers (snails) and filter feeders (Simuliidae)?
55
Trophic transfer efficiency 2/2
Overall, energy transfer is more efficient at each trophic level in the food web
Without external subsidy, trout would need 32% trophic transfer efficiency to persist in warm streams
With external subsidy, trophic transfer efficiency of ~9% is sufficient
O’Gorman et al. (2016) GCB
56
How do they sample fish?
Electrofishing to remove all trout from the experiment and check the treatments every two weeks
(3 passes of each 15 m reach)
Surber sampling to quantify body mass and abundance of macroinvertebrate community
(14 × 14 cm; 250 μm mesh; 5 samples per reach)
Rock scrapes to quantify body mass and abundance of diatom community
(scrape & measure upper surface area; preserve in Lugol’s)
57
How do they Quantify food web structure?
Gut content analysis under the microscope… and lots of it!!
49,324 direct observations of resource individuals in consumer guts
Yield effort curves constructed for every species in each stream
If <95% diet described by yield-effort curves, add links:
from species in the same genus
from same species in Hengill
from the literature
58
Trophic group biomass
in the trout river
Presence of trout led to a major decrease in invert biomass, but only in warm streams
Driven by snails and blackfly larvae
No change in invert biomass during the experiment in cold streams
Cascading effects on the diatom community
Increase in diatom biomass in the warm-fish treatment, no change in cold streams
Similar results for total chlorophyll, i.e. including cyanobacteria and green algae
Temperature-induced trophic cascade
59
Food web structure
definitions
Connectance = proportion of possible links in the web that are realised
Mean trophic level = average position of a species in the web
Consumer-resource ratio = no. of consumer species divided by no. of resource species
All three were significantly reduced during the experiment, but only in the warm-fish treatment
60
Autecological and synecological and consequences
Actively choose to feed on richer sources of energy (autecological)
Benefit from more efficient flow of energy through food web (synecological)
These mechanisms combine to help trout overcome the metabolic constraints of living in a warmer environment
This can lead to a simplification of the food web
But only at higher temperatures, where top-down control by trout is particularly strong
Simpler food webs are shown to be less stable
Robustness to extinctions declines with decreasing connectance (Dunne et al. 2002)
61
Explain how warming can lead to simpler and less stable food webs
Consequently, as temperature increases, the ratio of energy supply to demand decreases successively at each higher trophic level, and thus, increases the relative extinction probability of species populations at the upper vs lower ends of a food chain.
62
What is the temperature size rule?
The temperature-size rule denotes the plastic response (i.e. phenotypic plasticity) of organismal body size to environmental temperature variation.[1][2] Organisms exhibiting a plastic response are capable of allowing their body size to fluctuate with environmental temperature. First coined by David Atkinson in 1996,[3] it is considered to be a unique case of Bergmann's rule[1] that has been observed in plants, animals, birds, and a wide variety of ectotherms.[2][4][5][6][7] Although exceptions to the temperature-size rule exist, recognition of this widespread "rule" has amassed efforts to understand the physiological mechanisms (via possible tradeoffs) underlying growth and body size variation in differing environmental temperatures.
63
Biological insurance
Different species can perform similar roles – insurance against biodiversity loss?
E.g. pollination has evolved independently and repeatedly in insects, reptiles, mammals & birds
So, how many species can we afford to lose?
64
What are the multiple stressors on the world?
Species extinction
Global warming
Overpopulation
Pollution
Loss of rainforests
fossil fuel dependency
65
Threats to freshwater ecosystems
Acidification
Chemicals
Warming
Drought
Flooding
66
Causes and solutions to freshwater acidification.
The accelerated burning of fossil fuels over the past two centuries has largely contributed to the acidification of freshwater ecosystems.
Freshwater acidification occurs when acidic inputs enter a body of fresh water through the weathering of rocks, invasion of acidifying gas (e.g. carbon dioxide), or by the reduction of acid anions, like sulphate and nitrate within a lake.
Lakes that have been acidified by acid rain can be neutralized by liming, the addition of limestone (CaCO3).
67
The impacts of acidification on freshwater ecosystems
Acidification of freshwater ecosystems may have significant negative effects. Changes in pH as a result of freshwater acidification imposes physiological challenges on individual organisms, may decrease native biodiversity, and can alter ecosystem structure and function entirely.
Invertivorous river birds can suffer from direct toxic effects of aluminium combined with indirect effects of reduced food supply in acid streams
E.g. declines in UK Dipper (Cinclus cinclus) populations in upland areas during 1970s and 80s (Tyler & Omerod 1992)
68
Acid pulses in freshwaters
Coniferous vegetation catches mist & fog precipitation and the acidifying pollutants it carries
Surface run-off leads to acid pulses during storm events and spring ice-melt
pH often dips markedly over short timescales (especially in streams)
69
Ecological issues: declining health of fish
Gills are finely-divided with a high surface area: volume ratio
High labile aluminium at low pH causes mucification of the gills
Excess mucus clogs the respiratory surface, degrading gills & suffocating the fish
70
Effects of acidification with freshwater algae
Algal resources typically decline in acidified streams
Sensitive species like mayflies and snails disappear
Brown pathway dominants
Hardy species like worms and dragonflies thrive
71
Direct & indirect effects of acidification
Direct toxic effects - e.g. aluminium induces clogging of fish gills
Indirect food web effects - e.g. plants don’t do well in acidified environment; shift to detrital resources alters functional composition of higher trophic levels
72
The losers and winners of acidification
Trout & invertebrate herbivores (mayflies, snails) are lost from the “green” pathway
Large invertebrate predators and detritivores dominate the food web in the absence of fish and herbivores
73
Solving issues like acidification
Short term chemical solutions, e.g. liming to raise pH (lime is highly basic)
But artificially raising pH in acidified catchments is extremely expensive
It doesn’t mimic natural chemical change and may create problems of its own
Not a viable long-term solution
74
Salt marsh die-off
due to drought
Salt marsh die-off shown to alter the distribution of marsh snails, Littorina irrorata
To avoid predation by marsh crabs, snails aggregated on the border of retreating cordgrass, Spartina alterniflora
Compounded the die-off by intense grazing at the margins
Exclusion experiments showed that cordgrass recovers if snails are prevented from overgrazing
Drought causes not only direct die-off, but indirectly through altering animal behaviour (Silliman et al. 2005)
75
Impacts on interaction strength
Interaction strength is the magnitude of the effect of one species on another
Shown from a whole range of ecosystems that distribution is skewed towards weak interactions (Wootton & Emmerson 2005)
Demonstrated that coupling of strong and weak interactions facilitates switching between resources when densities become low
This promotes stability by avoiding extinctions (McCann et al. 1998)
Reduction in the number of weak links in the drought treatments
Weak interactions are important in promoting stability (McCann et al. 1998)
Drought is likely to reduce the stability of stream ecosystems.
76
Time & Space in Evolution
Two factors – evolution (time) and
isolation (space)
* Creates heterogeneity between
systems
* Importance of evolution in
geologically ancient habitats – can
you name some?
* Endemic species – evidence of
adaptive radiation
* Not northern temperate lakes –
why?
77
First summary for evolution of freshwater
F’water diversity often high, specialised and
endemic due to isolation and geological stability
* Morphological and genetic differentiation
* Important evolution models – charr, cichlids
* Common to fishes – taxa bias?
* Ecological Speciation
* Adaptive Radiation -needs “Space” with distinct
habitats
78
what is adaptive radiation?
In evolutionary biology, adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into a multitude of new forms, particularly when a change in the environment makes new resources available, alters biotic interactions or opens new environmental niches.
79
What is Dispersal?
Movement from one discrete patch to another
(Lincoln, 1998)
* Movement from point of origin
* Highly contentious (Benton et al. 2012)
* Not the same as “migration”….but migration
can be part of dispersal
* Does not have to involve colonisation or gene
flow
80
lotic vs lentic species
The term lentic (from the Latin lentus, meaning slow or motionless), refers to standing waters such as lakes and ponds (lacustrine), or swamps and marshes (paludal), while lotic (from the Latin lotus, meaning washing), refers to running water (fluvial or fluviatile) habitats such as rivers and streams.
81
Dispersal among Lentic Systems
Lotic issues apply
* Connectance is key
* Metapopulations more likely
* Interactions can cause local
extinction, i.e. sinks
* Connectance + Time =
successful Dispersal, Hien et al
2011.
82
Second Summary to evolution in freshwater
Dispersal is more than movement
* Determines genetic structure of populations
* Contributes to Landscape scale diversity
* Can be part of metapopulation
* “Fish” populations are heterogeneous movers
* Connectance is key at larger spatiotemporal
scales
* Species interactions play a large role in successful
dispersal and colonisation
83
Space and Scales
Large scale regions with high productivity have
greater biodiversity
Determined by Beta diversity increasing with
productivity at higher spatial scales
Chase & Leibold, Nature 2002
“Greater role of stochastic assembly than
deterministic as productivity increases”
84
Summary of
Dispersal in Communities
Dispersal a key process in colonisation and
community assembly
* Invasion sequence could lead to multiple
stable states
* Results relatively consistent between field and
lab studies
* Dispersal of predator and prey both important
* Connectance , and time, governs dispersal
85
What is the role of sexual selection in sympatric speciation?
his prediction leads to a hypothesis that sympatric speciation by sexual selection tends to occur as predation pressure is reduced (with other conditions unchanged) by, for example, a population entering into a new enemy-free habitat such as an island or a lake.
Since sympatric speciation occurs in the same geographic area there needs to be a driving force behind the divergence of the traits in the species, leading to speciation. If we add in the factor of sexual selection, this can lead to specific individuals seeking specific traits in their mates.
86
What is “biodiversity”?
Species’ presences and abundances
Species, traits and genes
Describes the range of ‘things’ present in a place and time
At different levels of biological organisation (genes to landscapes)
At different spatial scales (small sample to whole world).
87
Photosynthesis
Most photosynthesis is oxygenic, e.g. phytoplankton, macrophytes.
Dissolved O2 (D.O.)
in an English Chalk Stream
* Diel (day/night) changes in
concentration
* Oxygen production strongly
dependent on solar radiation
* Imbalance of photosynthesis
and respiration by night
* Modified by water-air
exchange (diffusion)
88
Anoxygenic & Chemosynthesis
Anoxygenic photosynthesis occurs where sulphide is present, also
on and in sediments, e.g. Chlorobium, Chloroflexus
89
Cyanobacteria
nitrogen fixing and O2 producing
- bloom forming – exhibiting fast growth
in low O2 and N conditions
- contain vacuoles that affect their
buoyancy – surface slicks
- can manipulate these vacuoles –
competitive advantage
- linked to toxins in freshwaters…a
recreation and drinking hazard
90
Periphyton
Photosynthetic
microorganisms that live in
biofilms attached to
submerged surfaces
* Algal components:
– cyanobacteria
– microalgae
– filamentous algae
* Biofilm also includes:
– polysaccharides
– detritus
– heterotrophic bacteria
– protozoa
91
Bryophytes (mosses & liverworts)
lack true roots
* grow attached to firm substrates
* Fontinalis antipyretica in clear
turbulent waters
– adapted to low light in
forested upland streams
Sphagnum moss in bogs (Mer
Bleue Bog, Ottawa, Canada)
* Can hold >20 times their dry
weight in water
* Helps to retain water during dry
conditions
92
Vascular plants
Angiosperms
* have true roots
* found in
– sluggish flowing waters
– wetlands
– shallow lake margins
Can be classified by life-forms
– emergent (9.17)
– floating emergent (9.15)
– submergent (9.16)
– free-floating
occur in zones of differing
water depth
93
Emergent macrophytes
perennials with large rhizomes
– can expand rapidly through belowground growth
– common reed (Phragmites)
– bulrush or cattail (Typha latifolia)
habitats
– wetlands
– shallow waters (<1.5 m deep)
optimal access to both light and nutrients
– access nutrients from the sediment
– photosynthesis above water surface
94
Adaptations to anoxic sediments
Diffusion of CO2 and O2 is
10,000 times faster in air than
in water
O2 transported to rhizome
(roots) by living and even dead
stems (culms)
cavities or spaces (lacunae)
make up to 70 % of the plant
volume (hollow stems)
-provides O2 to tissues buried in
waterlogged anoxic soil &
sediment
95
Submerged macrophytes
For example, pondweed (Potamogeton)
– occur to depths of about 10 meters in
clear lakes
* water provides buoyancy
– less need for structural tissue (lignin)
* rarely nutrient-limited
– nutrients absorbed from water through
foliage
– nutrients absorbed from sediment
through root and rhizomes
– translocation in both directions.
96
Macrophytes v phytoplankton
sequestration of nutrients by macrophytes may limit the growth of
phytoplankton
* abundant phytoplankton absorb light in the water column and may
limit light availability to submerged parts of macrophytes
* alternative stable states
– clear macrophyte dominated
– turbid phytoplankton dominated
*
state may also depend on planktivores & predatory fish
– trophic cascades
97
The building blocks of freshwater life (C,N,P)
Carbon is the most crucial element
for the formation of biomass in the
food web
* But nitrogen and phosphorus are
essential nutrients that give it
vitality
* Nitrogen is a major component of
chlorophyll and amino acids (the
building blocks of protein)
* Phosphorus is a vital component
of ATP (the energy unit of plants)
* Other important elements include
sulphur, silicon, iron, etc. (see
Chapter 14)
98
Elemental stoichiometry
Carbon to nitrogen ratio is a key
determinant of the “quality” of
resources in freshwater
* A high C:N ratio equates to a lowquality resource
* Nutrient poor, takes longer to
decompose
* A low C:N ratio equates to a highquality resource
* Nutrient rich, need to consume
less material for growth and
reproduction
99
Denitrification
A respiratory process in which NO3
- and other inorganic N forms are
used to oxidise organic matter leading to formation of N2
– Dissimilatory nitrate reduction
* Undertaken by some bacteria, the denitrifiers
– E.g. Paracoccus denitrificans, Thiobacillus denitrificans, and
some pseudomonads
Denitrification occurs where O2 is depleted
– Some bacteria use nitrate instead of O2 as a terminal electron
acceptor in respiration
– Requires an organic-rich, O2-poor environment
– Waterlogged soils, groundwater, wetlands, poorly ventilated
hypolimnion
* Denitrification is very important to reduce pollution in areas with
heavy agricultural or industrial inputs of DIN
* E.g. denitrification is promoted as a management tool to remove
nitrate from sewage or fertilisers in wetlands & riparian zones
100
Perennial vs. Intermittent vs. Ephemeral Streams
Streams are classified by different jurisdiction in different ways. Regulations differ, and are not applied consistently.
Perennial: A stream that has flowing water year-round during a typical year. The water table is located above the streambed for most of the year. Groundwater is the primary source of water for stream flow. Runoff from precipitation is a supplemental source of water for stream flow.
Intermittent: A stream that has flowing water during certain times of the year, when groundwater provides water for stream flow. During dry periods, intermittent streams may not have flowing water. Runoff from precipitation is a supplemental source of water for stream flow.
Ephemeral: A stream that has flowing water only during or for a short duration after precipitation events in a typical year. In many states, this term refers to streambeds that are located above the water table year round and streams where groundwater is not a source of water for the stream.
101
Wetland Hydrology
Hydrologic regime is the most important
abiotic factor determining wetland ecology
Permanence
Predictability
Seasonality
Hydrological characteristics have
consequences for biodiversity
* Regional and landscape
links/ variability
* More variability = more
diversity (see later lectures)
102
Physiography of rivers
Before we can understand the ecology, we must study
the morphology and geology….
1st Characterisation
* Discharge
* Catchment area
* Tributaries
Then…
* Physical habitat
Finally…
* Vegetation
103
Stream order classification
Higher order streams have a longer individual length
* But there are many more lower order streams per catchment
* Thus, lower order streams have an overall combined longer length
* Lower order streams often dominate the interaction between land and water
104
Meanders and Braids
Unless otherwise constrained, streams and rivers will meander
* Self organising – fractal geometry
(Stolum, 1996)
* Erosion & deposition exaggerate
meander over time
* Faster flow picks up sediment on
outside bend
* Slower water deposits sediment
on inside bend
* Point bar forms
Can cut through and cut-off
to form an oxbow lake
Over softer sediments and shallow water,
braiding may develop
This involves the main channel splitting and
combining in a braided pattern
Can be very variable over time
Channels form and disappear at fast pace
105
Primary production
The production of organic matter
from CO2 and nutrients using either
light energy or chemical energy
* Photoautotrophs obtain energy
from light
– oxygenic photosynthesis
– anoxygenic photosynthesis
Chemoautotrophs obtain energy
from the chemical oxidation of
inorganic compounds
– methanogenesis, sulphide
oxidation, nitrification
– often extremophiles living in
hostile environments, such as hydrothermal vents
106
Carbon cycling
Primary production also plays a key role in the carbon cycle
* Photosynthesis converts inorganic carbon (CO2) to organic carbon (i.e. the
kind that can be eaten by animals – heterotrophy)
* Heterotrophic & anoxic respiration change organic carbon to CO2
* Methanogenesis/methanotrophy converts CO2 to CH4
107
Submerged v emergent macrophytes
emergent plants benefit from greater access to light and CO2
* cost is need for large amounts of structural material (lignin) in stems
* submerged plants benefit from lower structural investment
* cost is slow diffusion of CO2 in water
* floating leaves at water surface benefit from contact with air, but
without cost of synthesising large amounts of structural material
108
N- or P-limitation
Seston N:P of 25 to 30 delimits transition from N-limitation to P-limitation at ecological scale
N-depleted waters are often dominated by cyanobacteria
Cyanobacteria can fix N2 from air
Brings an external source of nitrogen into freshwaters
109
Key components of the nitrogen cycle
There is very little nitrogen in rocks
* Abundant in the atmosphere (78%)
* But not available to most organisms
(including all higher plants)
* Some bacteria can fix N2 gas into
organic N (useable)
* Most planktonic N-fixation performed
by cyanobacteria
Major forms of organic nitrogen include:
– protein
– nucleic acids
– amino acids
– urea
* Urea is particularly important because it
is excreted by air-breathing organisms
* Most freshwater organisms directly
excrete ammonium (NH4
+), however
* Organic nitrogen is also decomposed to
form NH4
+
* Soil leachate and sewage discharge are
also sources of (dissolved) organic
nitrogen in freshwaters
Dissolved inorganic nitrogen mainly consists of ammonium (NH4
+),
nitrite (NO2
-
) and nitrate (NO3
-
)
* Under high pH, NH4
+ is converted to ammonia gas (NH3) and can
dissipate to the atmosphere
* Highly toxic to aquatic organisms
* Nitrite is also toxic, but usually found in low concentration
* There are occasionally trace amounts of nitrous oxide (N2O)
* Aquarium lovers will know the importance of introducing NH4
+ to a new
tank (either directly or with hardy fish)
* Converted to NO2
- then NO3
- before delicate fish can be introduced
Only bacteria & archaea can fix nitrogen
– in cyanobacteria, N2 fixation often occurs in specialised cells,
called heterocysts (Figure 14.1), e.g. Anabaena
– requires large amounts of energy (ATP)
– inhibited by O2
* Some freshwater cyanobacteria form large globular structures
(e.g. Nostoc)
* Inedible, so nutrients only enter food web once decomposed
110
Key component of the phosphorus cycle
Unlike carbon and nitrogen,
phosphorus is mainly found in only
one inorganic form
* Phosphate (PO4
3-
)
* Dominant in natural waters, but
often undetectable in pristine waters
Organic phosphorus
occurs in cells as nucleic
acids, phospholipids, and
other compounds
* Cells can also store
phosphate as a polymer
(polyphosphate)
Main sources are weathering of minerals in rocks and soils,
agricultural runoff & decomposition of organisms
* Essential nutrient required for synthesis of DNA, RNA & phospholipids
* Often limiting in freshwaters due to binding by oxic soils
* Therefore, phosphates become soluble under anoxic conditions
* This has management consequences
111
What is an ecosystem?
All of the living things (organisms) and non-living things (abiotic factors) in a specific area
A single type of organism is a species
Every member of a species in one area is called a population
All of the populations in an area make up a community
The species found in an ecosystem are determined by both abiotic factors and other organisms
112
Fluvial transportation
Rivers transport 3 main materials downstream – water, sediment & organic matter
Water & sediment affect shape of river channel
A change in either the flow of water or sediment load of the river can lead to increased deposition or erosion
E.g. Above a dam, water pools and slows, depositing much of its transported sediment; below the dam, there is increased erosion as the river tries to replace its sediment load#
113
Exceptions to the RCC
(River Continuum concept)
General theory of river ecosystems, does not work perfectly
Not all headwater streams receive leaf litter from forests
Many upland streams are dominated by algae and grazers
Variable importance of green versus brown pathway
114
Time & Space in Evolution
Two factors – evolution (time) and
isolation (space)
* Creates heterogeneity between
systems
* Importance of evolution in
geologically ancient habitats – can
you name some?
* Endemic species – evidence of
adaptive radiation
* Not northern temperate lakes –
why?
115
Summary of freshwater biodiversity
F’water diversity often high, specialised and
endemic due to isolation and geological stability
* Morphological and genetic differentiation
* Important evolution models – charr, cichlids
* Common to fishes – taxa bias?
* Ecological Speciation
* Adaptive Radiation -needs “Space” with distinct
habitats
116
Summary in dispersal
Dispersal is more than movement
* Determines genetic structure of populations
* Contributes to Landscape scale diversity
* Can be part of metapopulation
* “Fish” populations are heterogeneous movers
* Connectance is key at larger spatiotemporal
scales
* Species interactions play a large role in successful
dispersal and colonisation
117
Space and Scales
Large scale regions with high productivity have
greater biodiversity
Determined by Beta diversity increasing with
productivity at higher spatial scales
Chase & Leibold, Nature 2002
“Greater role of stochastic assembly than
deterministic as productivity increases”
Dispersal a key process in colonisation and
community assembly
* Invasion sequence could lead to multiple
stable states
* Results relatively consistent between field and
lab studies
* Dispersal of predator and prey both important
* Connectance , and time, governs dispersal
118
Food web stuff
Body size is an important determinant of consumer-resource interactions
Big things typically eat small things, which eat even smaller things
Aquatic systems in particular are highly size-structured
Consumers are often constrained to only eat what will fit in their mouth
Not all species interact with each other equally
Interaction strength is the magnitude of the effect of one species on another (Laska & Wooton 1998)
119
Flooding info
Discharge - volume of water that passes through a given cross section per unit time (usually measured in cubic meters/feet per second)
Stage - level of water surface over a datum (often sea level); as discharge increases, stage increases
Flood stage - stage at which overbank flows are of sufficient magnitude to cause considerable inundation of land and roads
Crest (or peak) - highest stage reached during a flood
The counter-intuitive process of increased frequency of both drought & flooding:
a) average summertime precipitation is predicted to greatly decrease
b) amount of extreme precipitation per year is predicted to greatly increase
120
What is “biodiversity”?
Species’ presences and abundances
Species, traits and genes
Describes the range of ‘things’ present in a place and time
