1
Q
Definitions of ecology, population, community, ecosystem
A
- Ecology = scientific study of interactions that determines the distribution + abundance of organisms (where organisms are and their density). Considers organisms at individual, population, community, ecosystem and biosphere levels
- Population: set of organisms of the same species in the same area
- Community: collection of populations of different species in the same area
- Ecosystem: combines communities and their abiotic environment
2
Q
Emergent properties of populations, communities, ecosystems
A
- Population: size, density, distribution, growth rate.
- Community: species composition, structure, function and species diversity, interactions (predation, parasitism)
- Ecosystem: patterns and processes of energy/matter that flows through the system - continuous input of energy (sun), recycling of matter, C, P & N cycles
3
Q
Proximal / ultimate explanations
A
- Proximal explanation: nearby environment of the organisms, react to stimuli in the immediate environment like tolerance limits - distribution of specific species often explained by preference for specific temp or soil type or avoidance of predators
> zooplankton vertical migration - light - Ultimate explanation: relate to the evolutionary context - the adaptive nature of specific traits and behaviors - why does a species show this specific set of tolerance limits?
> zooplankton vertical migration - fish avoidance - go deep during the day to avoid predation by visually hunting fish but feed on phytoplankton which rely on sunlight and are near the surface = go up at night
4
Q
What is the difference between a condition and a resource?
A
- Condition: abiotic environmental factor that varies in space or time e.g temp, pollutants
- Resource: any substance or energy that can be consumed by organisms e.g. food, water, space
- Both determine where an organism can occur + how good it performs
5
Q
Tolerance limits
A
- Range of environmental conditions that an organism can survive, grow and reproduce. Reproduction is the limiting factor - has narrowest tolerance limit
> Eury = tolerate a wide range of conditions, steno = narrow range
FIGURE
6
Q
Ectotherms/endotherms
A
- Ectotherm = body temperature accommodates to that of their environment, development time is dependent on temperature - in the sun they are active and fast e.g. alligators, plants
- Endotherms = produce heat by consuming food, have a thermostat to regulate body temp which is kept constant and high leading to a high metabolic rate and shorter reaction time. Need a lot of food during cold temps to keep metabolism and body temp up e.g. humans
7
Q
Air pollution and buffering capacity of waters - explain
A
- Acid rain: N and S oxides react with water to form nitric and sulphuric acid= acid rain. Acid rain can lead to acidification of weakly buffered systems like forests. Water bodies can contain sufficient amounts of (bi)carbonates to act as a buffer: adding H+ shifts reactions to produce water and neutralize the H+ ions to prevent a change in pH (no change in H+ conc = no change in pH = prevent effect on aquatic life). As long as there are bicarbonates in the water, buffering capacity remains intact. Areas rich with limestone = well buffered
> H2CO3 <-> H2O + CO2
> H2CO3 + OH- <-> HCO3- + H2O
> HCO3- + OH- <-> CO32- + H2O
8
Q
Why do brackish waters often contain few species?
A
Not many species can handle high salinity. Plants - high salinity is like drought for plants as root systems have to fight strong osmotic gradients to take up water. Aquatic animals: membranes are semi-permeable and salts are too large to pass through but water moves out of membranes as a result of osmotic pressure and they dry out.
9
Q
Give two examples of bio-indicators
A
- Can use occurrence of specific organisms as an indicator of air, soil or water quality as organisms differ widely in the degree they can cope with pollution
- Presence of viola calaminaria indicates soil contaminated with zinc
- Macroinvertebrates in rivers used to assess water quality/oxygen content. Macroinvertebrates are found in large quantities = easier to sample than other organisms. Worms can deal with low oxygen content whereas freshwater shrimp can only handle slightly low oxygen content waters
10
Q
What is PAR ?
A
Photosynthetically active radiation = EM spectrum between 400-700 nm = energy source used by green plants - use light to convert CO2 and water to oxygen and glucose which can then be used to grow + consumed by organisms. Chlorophyll absorbs light of this range
11
Q
Compensation point
A
- PAR-intensity where net photosynthetic rate = 0 so gross photosynthesis = losses due to respiration + other causes - determined by amount of photosynthetic pigments. Plants that thrive with high sun often have higher light compensation points
- Plants can survive periods of lower light intensities than compensation point but in long term, average must be above compensation point for plant to survive
- First, net photosynthesis increases with increased radiation as there is more PAR available until it reaches light saturation point = max photosynthesis. Then at too high light intensities, photosynthetic rates decline because of damage from high light intensities
FIGURE
12
Q
What is a trade-off + illustrate with an example
A
- Trade-off: situation that involves a negative effect on one quality in return for gains of another
- Herbivores feed on specific/better parts of plants (seeds, young leaves) but selectivity takes time and thus they are less efficient = tradeoff. E.g. cows are bulk feeders - eat a lot but average quality is low
- Strong competitors are often more vulnerable to predation - allows inferior competitors to coexist with superior ones e.g. larger zooplankton are stronger + more competitive but also more vulnerable to predation by fish (visible predators)
- Competitive strength can reduce dispersal capacity e.g. large seeds
13
Q
Global hydrological cycle
A
How water cycles through Earth’s land, ocean, atmosphere. Precipitation, evapotranspiration, runoff, infiltration. rate of inflow = rate of water loss (until recently)
14
Q
Why is oxygen such an important variable in aquatic systems. Illustrate how aquatic organisms deal with this challenge.
A
- Oxygen is an essential resource for aquatic animals respiration + for decomposers to digest organic material
- Solubility of oxygen is limited - so can become limiting in aquatic habitats. Solubility is reduced at higher temps. - In organically enriched water bodies - higher temps increase bacterial activity decomposing organic material = more rapid consumption of oxygen PLUS lower solubility at higher temps = severe oxygen stress
- Aquatic organisms obtain sufficient oxygen through large gills, create continuous flow of fresh water over their gills, powerful respiratory pigments, breathing air at the surface
- Plants: mangrove trees occupy areas regularly flooded by seawater - their root systems are extensive + partly stick out of the sediment and contain air channels
15
Q
Autotrophs/heterotrophs
A
Autotrophic organisms (green plants, cyanobacteria): assimilate inorganic resources into organic molecules (proteins, carbs) that are available to heterotrophic organisms (decomposers, carnivores). Heterotrophs need organic energy-rich material as food.
16
Q
Importance of decomposers in the functioning of ecosystems
A
- Dead individuals + excretion products are a resource for decomposers (bacteria, fungi)
- Recycling of matter, removal of waste
17
Q
Predators/parasites
A
- Parasitism: parasites use living organisms as their food source - mostly do not kill their hosts and only have one or a few hosts during their life cycle
- Predation: predator kill and eat other organisms - also includes herbivores, kill many prey during lifetime
18
Q
In general, plants are less high quality food than animals. Explain why.
A
- Digestibility: plant less easy to digest, most animals can’t digest cellulose so digestive tract of herbivores is longer than carnivores
- C:N ratio of plant tissue is much higher than for animals. Animals have more N rich proteins (more rich in structural components)
19
Q
Ecological stoichiometry. Illustrate its importance with an example
A
Ecological stoichiometry: studies chemical composition of food. Not all prey are same quality - more closely prey is in chemical composition to the consumer, more efficient consumer is in transforming food into their own organic material. E.g. Herbivores feed on specific/better parts of plants (seeds, young leaves) but selectivity takes time and thus they are less efficient. E.g. cows are bulk feeders - eat a lot but average quality is low
20
Q
The C:N ratio in animals and plants differs. Discuss two consequences.
A
- C:N ratio of plant tissue is higher (40:1), animals have more N rich proteins (C:N ratio of 8-10:1). Herbivores have food source too rich in C, too low in N so are specific with what they eat - prefer seeds, young leaves over twigs and stems (contain little useful material). Decomposers prefer N rich
- Fecal material of herbivores contain lots of C = many organisms specialize on fecal material of herbivores while excretion product of carnivores contains no food source anymore
21
Q
Inducible defences – illustrate with examples. What is the advantage of defences being inducible?
A
- Inducible defense = defense only produced when prey is exposed to predator risk. Don’t waste energy on defenses when they are not needed, only when they have to protect themselves.
- E.g. plants produce higher amounts of substances that reduce digestibility of their leaves when insects start to feed on their leaves, diel vertical migration in zooplankton
22
Q
Warning colours
A
- Striking colour patterns suggest they are toxic or taste bad. E.g. wasps, some toxic snakes, butterflies
- Some species have evolved to mimic these species without investing energy in the production o the chemical defense e.g. hover flies that mimic wasps
23
Q
Essential/perfectly substitutable/complementary/antagonistic resources
A
- Distinguish between essential and nonessential (substitutable) food resources
- Graphs: x and y axis is amount of given resource, isoclines = connect points of same value: A = zero population growth, B = intermediate, C = high population growth
- Essential: population growth requires that both resources are present. Population growth realized at given concentration of one resource is dependent on the conc of the other. E.g. plants need both N and P, adding more N will not increase growth if P is limiting
- Perfectly substitutable: population growth determined by combined amount of two resources, food sources are (almost) 100% equivalent e.g. different kinds of grains for chickens
- Complementary: total conc of resources needed to sustain a given pop growth rate is lower when both resources are present than when only one resource is present - resources complement each other e.g. rice (rich in sulfur) and beans (rich in proteins)
- Antagonistic: organisms need a higher amount of resources when both resources are present - resources interact and form detrimental side products e.g. become toxic when combined
- Inhibition: resources become limiting when present at too high concentration e.g. too much light is detrimental for photosynthetic activity
FIGURE
24
Q
Niche
A
- Ecological niche is an n-dimensional hypervolume determined by environmental conditions and resources in which a species can build up a viable population. Determined by tolerance limits of the species for all possible environmental factors (n), including conditions and resources.
- Often limit analysis to 3 axes: food spectrum, use of space, use of time
25
Fundamental niche / realised ecological niche.
- Fundamental niche = determined by tolerance limits, reflects physiological characteristics, quantified in the lab
- Realized niche = niche as is achieved by the species under natural conditions (can be equal to fundamental but normally smaller because of interactions with other species - interspecific competition, predation, parasites)
FIGURE
26
Can a realized ecological niche be larger than a fundamental ecological niche?
No, refer to figure
27
How does one determine a fundamental ecological niche, and a realized ecological niche?
Fundamental = standardized laboratory experiments
Realized = measured in nature
28
Demography. What are the main drivers of changes in population densities ?
- Demography investigates the number of individuals in a population and the changes over time.
- Births + immigration - deaths - emigration
29
How can one estimate absolute population sizes?
- Absolute = count all individuals of a population - difficult especially for mobile organisms or large populations
- Samples: estimate absolute density by using random samples sufficient in size
- Capture-recapture: estimate absolute density by capturing x amount of individuals, marking them, release them then organize a 2nd sampling. Marked individuals are mixed randomly with all individuals of the population - can calculate total pop size: m*/n = M*/N. can only be applied to mobile organisms, probability of capturing marked and non marked should be equal, marking should not affect probability of death
> m = marked organisms in 2nd sample, M = total number of marked individuals (marked in first sample)
> n = size of 2nd sample, N = total number of individuals in population
30
Catch per unit effort (CPUE). Illustrate its usefulness with an example.
- CPUE indicates how population evolves over time/ relative population density.
- Scale the amount of caught individuals to the effort taken to catch the individuals
- E.g. commercial fishing - choose best location for fishing and detect overfishing
31
How can one quantify the degree of aggregation of individuals in a population?
- Degree of aggregation = s2/x = level of variance/avg density
= 1, random
<1 regular, little change between samples
>1 aggregated, lots of variance between samples, common
FIGURE
32
What are the causes of aggregated patterns in natural populations? (two main classes of causes)
- Heterogeneous environment and organisms have a preference for a specific microhabitat - survive and reproduce better in that microhabitat e.g. location of food
- Organisms are actively attracted to each other and aggregated distribution means probability of encountering an individual is increased
33
Why do organisms swarm in the presence of predators?
- Increases vigilance, more animals to detect the predator = faster reaction + warn others
- Confusion effect: harder to focus on one target
- Dilution effect: less chance you will be the prey
- Some swarm in time e.g. mayflies come out of water at the same time - more easy to find partners and reduced chance of being prey
34
Mutualism / competition / contramensalism
- Mutualism (++): interaction that causes increase in population size for both interacting species
- Competition (--): both interacting partners experience harm so that equilibrium population size is reduced. Is a result of organisms sharing resources (intraspecific competition is high as they share many resources). Often it is worse for one partner than the other
- Contramensalism (-+): parasites and predators. Predation - negative impact on population is often less than number of kills (kill ill, young or old prey, less intraspecific competition)
35
Exploitation / interference competition
- Competition (--): both species reduce equilibrium population size, often one more than the other
- Exploitation/indirect: competition experienced due to lack of resources (limiting)
- Interference/direct: interacting species lose time and energy interfering with each other e.g. birds chasing each other away from feeder
36
Intra / interspecific competition
- Intraspecific competition: competition between organisms of same species, important for population regulation. Mortality and birth rate intersect at a given density (balance each other out = equilibrium) = carrying capacity. Lower than carrying = population grows. Higher = shrink in size due to reduced birth rates or increased mortality. Capacity is dependent on the species and the environment + can vary in time e.g high density beetle population led to lower densities at the end of the experiment as they ate all the food, no food = mortality
- Interspecific competition: competition between individuals of different species. individuals of one species reduce birth rates/increase death rates of another through competition for a shared resource. Species can coexist because environmental conditions never remain constant long enough to allow a species to drive the other extinct.
- Species can only coexist if intraspecific competition is stronger than interspecific competition for both species. Niche differentiation encourages coexistence (reduced niche overlap + interspecific comp).
37
Carrying capacity - explain
Mortality and birth rate intersect at a given density (balance each other out = equilibrium) = carrying capacity. Lower than carrying = population grows. Higher = shrink in size due to reduced birth rates or increased mortality. Capacity is dependent on the species and the environment (limited by energy, water, food, space) + can vary in time
FIGURE
38
Net recruitment
Difference between births and deaths = net recruitment = determines growth. When conditions are not limiting, population increases exponentially as growth is determined by producing offspring but then resources become limiting and pop growth determined by amount of competition. Growth declines until zero net growth = carrying capacity. Net recruitment is highest/ pop growth rates are highest at intermediate pop sizes
FIGURE
39
Logistic growth equation
- Population growth is dependent on intrinsic rate of natural increase (r), population size and corrected by coefficient ((K-N)/K) that quantifies resource limitation. K is carrying capacity
- dN/dt=rN((K-N)/K)
- Assumes linear decline in population growth with population density (not really accurate for most populations)
- Intrinsic rate of natural increase, r determines growth rate in species with overlapping generations
Resources not limiting: dN/dt = rN
FIGURE
40
Sustainable exploitation of populations
- Sustainable exploitation = using resources at a level that can be sustained indefinitely -> harvesting at a level that compensatory population growth is possible. Harvesting to levels higher than half of carrying capacity gives possibility of recovery
- Like with predators reducing population size = intensity of competition is reduced = higher net recruitment = faster population growth = party (or completely) compensating for loss due to predation
41
How can one study the impact of predators on species densities and community composition of prey?
- Impact is often less strong than number of individuals killed: go for ill, young or old prey; prey populations limited by other reasons e.g. food; if predators reduce pop size, net recruitment increases and compensate for the loss
- If predator prefers competitive organism it has a positive impact on species diversity - coexistence between inferior and superior competitors e.g. bigger zooplankton are more competitive but have a higher chance of being prey to fish. Bigger seeds are harder to disperse
- Direct effect = killing of prey, indirect = presence of predators can change ecology of prey populations
- CPUE - can detect overfishing
42
Functional response of predators
- Functional response of a predator is the relation between amount of prey in habitat and amount of prey consumed by an individual predator, determined by search + handling time. It quantifies the amount of food a predator gets depending on density of prey and shows the impact a predator has on prey populations. The fact that predators are limited in amount of prey they can handle = good for prey. As prey pops become less dense, impact of predators is stronger - predator prey populations tend to oscillate
- Type 1 functional response: typical for filter feeders - linear increase in prey uptake with prey density until max feeding rate is reached and stays constant. All time devoted to handling time
- Type 2: typical for invertebrates, most common. As prey density increases, searching time decreases until it becomes zero. Then max feeding rate is reached (determined by handling time). Less linear as the amount of time invested in handling prey increases with amount of prey eaten
- Type 3: typical for vertebrate predators - ignore species at low abundance (increasing their searching efficiency). Learning behaviour = reduces handling time = higher max feeding rate
FIGURE
43
Ideal free distribution
Predators distribute themselves over 2 habitat patches so on average they have the same food intake - move away when food intake decreases. Ideal free assumes that the predators are not being disturbed by other factors e.g. ducks on pond - go where more of the food is
44
What is the reason of the high diversity of parasites?
- Virtually no organism is free of parasites
> microparasites are small and have pop growth upon colonization of their host - can have large population within single host individual e.g malaria
> Macroparasites are larger, do not reproduce on their hosts - produce eggs that are released from their host to infect other hosts e.g. schistosoma worms
- Very specialized - infect specific organs. Many show strong adaptations to increase production of infective stages or increase transmission success
45
Illustrate with two examples how parasites are adapted to increase their transmission efficiency
- Their habitats are living organisms that show defence systems = host-paraiste arms race = coevolution = increasing specialization
- Manipulation of host behavior e.g suicidal behaviour of - Mantis religiosa when infected by Gordia
- Castration of host: effective method to allocate energy from host to parasite while enabling host to survive and thus keeping parasite alive
46
Prevalence / infection intensity
Prevalence = fraction of host individuals that are infected, infection intensity = avg number of parasites on infected hosts. Abundance of parasite = prevelance x intensity
47
Give 4 examples of mutualistic interactions
- Pollination by insects: fertilization of plants and pollinator gets food (nectar and pollen)
- Microbial flora in digestive tract of herbivores help digesting plant material
- Agriculture: It is thanks to the domestication of plants and animals for food that we have been able to achieve such high population growth rates. At the same time, the population sizes of cattle, chicken, wheat and other domestic organisms have also increased dramatically
- Cyanobacteria associate with the root system of the plant and are fed by the plant; in exchange, the plant gets extra nitrogen
48
Is agriculture a mutualistic interaction?
Yes - it is thanks to the domestication of plants and animals for food that we have been able to achieve such high population growth rates. At the same time, the population sizes of cattle, chicken, wheat and other domestic organisms have also increased dramatically
49
Explain why there are so few trophic levels in an ecosystem.
- With each step in the food chain, a lot of the energy (>90 %) is lost: part of the energy is captured through the assimilation of organic material into own tissue, but a large part is lost through excretion and respiration
- Solar radiation -> autotrophs -> herbivores -> carnivores (+decomposers degrading dead organic material at all levels)
- Aquatic ecosystems often have four trophic levels (algae – zooplankton – planktivorous fish – piscivorous fish)
50
Explain the loss of energy at a given trophic level. Illustrate with a figure.
Loss of energy: only some of the available organic material is consumed, only some of the consumed material is digestible (rest is excreted), respiration is needed to keep metabolic functions + keep body temp at constant level
51
Ecological yield
- the ratio between the amount of production at a given trophic level to the amount of production at the lower trophic level. It quantifies the losses of energy for each trophic level. Ecological yield is mostly very low, less than 10%
> Pn+1/Pn
- River Ecosystems: decomposer food web is even more important because almost all energy flows through decomposer food web - rivers characterized by very low level of primary production
52
Bottom-up / top-down control
- Bottom-up: abundances + species composition mainly determined by amount + type of resources aka by characteristics of the lower trophic level e.g. biomass + species competition of phytoplankton in a lake determined by availability of nutrients
- Top-down: abundances + species composition mainly determined by predation aka higher trophic level e.g. biomass + species competition of phytoplankton in a lake determined by zooplankton grazing
53
How can one study whether a given trophic level is bottom-up / top-down controlled?
- If community has one trophic level = it is automatically bottom-up controlled
- If there are 2 = highest level is by definition bottom up controlled. Means that food must become limiting and implies that the highest level has a strong impact on the first trophic level which is then top-down controlled.
- If there are three, the upper one is bottom-up control, implying that the second one is top-down. It cannot exert a strong impact on the lowest level, which is then bottom-up controlled.
- Not mutually exclusive - can change over time. Primarily depends on which is limiting
- Carry out field experiments in which food resources and/or predation levels are manipulated
FIGURE
54
Illustrate the key differences in food web structure in a river and a lake.
FIGURE
55
What is so special about food web structure of rivers?
- Almost all energy flows through decomposer food web (larger input of organic matter from the drainage basins)
- Source of carbon comes from outside the aquatic system
56
How can one measure primary production in a lake?
- Primary production = synthesis of biomass by autotrophs
- Clear bottle-dark bottle method: a number of clear and dark bottles are filled with water and incubated in the lab.
> Clear = light can penetrate and algae engage in photosynthesis. Net change in oxygen conc over a given period = net photosynthetic rate = net primary production.
> Dark bottles = algae cannot photosynthesize but they do respire and consume oxygen - measuring decrease in oxygen conc quantifies amount of respiration
- Gross primary production = oxygen produced in clear bottles + respiration from dark bottles
FIGURE
57
In lakes, it is important to determine vertical profiles of primary production. There is a specific relationship between the depth profile of primary production and the trophic state of a lake – why / explain.
- Primary production = synthesis of biomass by autotrophs. Photosynthetic activity depends on light. Deeper = less light
- GPP = gross primary production, R = losses by respiration, NPP = net primary production
> NPP = GPP - R
> Depth at which GPP = R is the compensation depth (NPP = 0)
> Compensation depth is more shallow as productivity increases as higher densities of algae at the top absorb more light
- Bi) nutrient poor
- iii) highly eutrophic (nutrient rich)
FIGURE
58
Diversity index of Simpson
-Takes into account species richness (number of species that occur) and evenness (relative abundance of species)
- S = number of species, Pi = fraction of community made up of species i
- Sum = measure of concentration: quantifies probability that 2 individuals randomly drawn from the community belong to the same species
EQUATION
59
Biodiversity
More encompassing than species diversity - also includes genetic diversity and diversity in communities and landscapes
Aquatic Ecology
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