Basic terms and concepts Flashcards
ecosystem
community of biotic and abiotic components which are linked by nutrient and energy cycles and interacting as a system
food web
the totality of interacting food chains in an ecosystem. It describes how the energy flows in the system
population
group of individuals of the same species, which live in the same demographic region, time and are genetically connected over generations
abundance
density of organisms per unit of area/volume
biomass
mass of organisms per unit of area/volume, includes all parts of living organisms but not dead organisms or parts thereof
production
characteristic of the community, rate of C/energy is fixed, or new biomass is built over time
productivity
characteristic of the habitat, says how great the production could be (not community or population)
excretion
the elimination of waste products produced by the metabolism (e.g. urine, faces)
exudation
diffusive excretion of small molecular compounds (e.g. amino acids, monosaccharides) by plants or phytoplankton
ingestion
uptake of material into the digestive system I= A+E
assimilation
the incorporating of nutrients into the individual; A=R+P
gross growth efficiency
relation between production and ingestion; K1=P/I
net growth efficiency
relation between production and assimilation; K2=P/A
efficiency of energy transfer between trophic levels
between 0-30%, the higher organised an organism is, the lower the TTE → lower TL – higher TTE (very generalised) 𝑇𝑇𝐸 = 𝑃𝑝𝑟𝑒𝑑𝑎𝑡𝑜𝑟/𝑃𝑝𝑟𝑒𝑦
efficiency of consumption and assimilation
assimilation efficiency AE=A/I
consumption efficiency = 𝐼𝑛/𝑃𝑛−1 (n…. trophic level)
necromass
mass of dead material that is included in the biomass (bark, hardwood…)
primary production (PP)
C fixed (photosynthetically) or new biomass built
secondary production
rate of production of heterotrophs per unit of area/volume per time (can be used for somatic growth/reproduction)
P:B ration
production per biomass: growth rate at population or community level
autochtonous
materials produces within the system
allochthonous
material produced outside the system and transported into it (i.e. definition depends on system boundaries)
gross primary production
total C fixed via photosynthesis
net primary production
gross primary production - losses due to respiration + exudation/excretion
gross population growth rate (µ)
growth of new organisms
Which factors determine the trophic transfer efficiency how and why?
The higher an organism is organised, the higher are the losses due to respiration, good food quality raises the TTE, because the needed quantity shrinks
osmotrophy
ability to ingest and digest dissolved material
mixotrophy
ability to assimilate carbon dioxide (photosynthesis and chemosynthesis) and ingest and digest organic particles (phagotrophy) and dissolved material (osmotrophy)
omnivory
ability of animals to feed on plant and animal matter
allometry
body size correlates with weight specific metabolic rates (ingestion, production, respiration, excretion)
Metabolic Theory of Ecology (MTE)
Very short: the metabolic rate of organism is the fundamental biological rate, which is the base for the most observed pattern in ecology
grazing chain
food chain based on autotrophs (plants), herbivores and carnivores
detritus chain
food chain based on detritus (dead biodegradable material) and detritivores (detritus eating bacteria and other microorganisms) and consumers
grazing vs detritus chains in pelagic/terrestrial habitats
- pelagic: grazing chain more important, because the majority of the NPP is consumed by herbivores (usually complete swallowing of the prey) – less detritus occurs
- terrestrial: detritus chain is more important, because herbivores consume only a small part of the NPP, especially in forests, more detritus occurs
trophic cascade (HSS)
A change in the production of an ecosystem trough the indirect influence of a population on a higher TL on a population of lower TL (e.g. carnivore consumes herbivores → more plant biomass can be built)
trophic level
integer, says how often substance got assimilated since the last fixation by the primary production (e.g. primary producers 1, herbivores 2, first rank carnivores 3, second rank carnivores 4 etc.)
trophic position
determined by the TL/TP the population is feeding on, doesn’t have to be an integer
bottom-up-control
regulation of the higher TL by the lower TL (many prey → many predators, positive correlation)
top-down-control
regulation of the lower TL by the higher TL (many predators → little prey, negative correlation)
upper limit to the size ratio between predator and prey
max ratio terrestrial: 1000:1, pelagic: 1.000.000:1 (If the predator is getting to big, the uptake of the prey is not energetically worthwhile anymore)
„stability” of an ecological system
There isn’t one definition of THE stability in ecology. There are just stability properties like persistence, resistance and resilience.
Persistence
Outlast/Survival of an ecological system, e.g. preservation of the species inventory
Resistance
remain essentially unchanged despite potential disorders
Resilience
return to the initial state after a change due to temporary disturbances (subsumes elasticity (=speed of return to the initial state) & area of attraction (= all the states from which the initial state is reached again)
taxonomic diversity
Simpson-Index 𝐷=1−Σ𝑝𝑖2𝑠𝑖=1 p…proportion of specie)
𝐷𝑚𝑎𝑥=1−𝐷𝑠 (s…specie number)
𝐸=𝐷𝐷𝑚𝑎𝑥 (E…evenness)
Simpson – relies more on evenness than specie number
Shannon-Wiener 𝐻′=−Σ(𝑝𝑖log(𝑝𝑖))𝑠𝑖=1
𝐻′=log (𝑠)
E = 𝐻′/𝐻′𝑚𝑎𝑥
SW relies more on species number than evenness
The recycling of resources from dead org. material occurs mostly via bacteria and fungi (almost only relevant in terrestrial systems → why?!)
The most fungi are obligate aerobe
In terrestrial system fungi are the main decomposers of lignin, in open water ecosystems there isn’t lignin, → white rot
define biodiversity. How is it measured?
Biodiversity is the variety or richness of genes, species, populations and their interactions.
You can measure it with different indices (Simpson, Shannon-Wiener etc.) to compare different ecosystems, habitats etc…
How does biodiversity influence ecosystem functions and their spatial-temporal variability? What are the mechanisms?
Stability of ecosystem function increases with diversity, at first linear, then weaker → high biodiversity → low variability of ecosystem functions
The reasons are buffer mechanisms:
Compensatory mechanism between individual populations, positive covariance → less stable; negative covariance → more stable
Portfolio effect: the more individual populations the higher the probability of asynchronous fluctuations → negative covariance
Insurance Hypothesis: with high diversity the probability of an occurrence of different species with the same functions increases (negative covariance)
Facilitation: one species benefits from another
Complementarity: different niches
Jansen-Cornell effect: Probability of survival for seedlings of a plant (this hypothesis was postulated for tropic trees) increases with the distance to the next adult individual… one reason for the species richness in the tropes
factors influencing biodiversity: latitude
diversity is decreasing from the tropics to the poles
factors influencing biodiversity: extreme habitats
extreme habitats are low on species number, but (with enough productivity) rich in individuals and vice versa, temperate habitats are more diverse and often have fewer individuals per species
factors influencing biodiversity: productivity
productivity of the habitat: unimodal curve, maximum at medium productivity, with low productivity only specialist survive, with high productivity strong competition for light → plants grow very big → fewer individuals/area, with medium productivity the diversity is the highest, because different species are limited by different resources (Tilman model)
factors influencing biodiversity: IDH (Intermediate Disturbance Hypothesis)
the diversity is highest at (measured by the duration of the generation) mean interference frequency and Interference intensity; very frequently and strong disturbances → r-strategists; very seldom and weak disturbances → K-strategists; mediate frequency and intensity → both strategists are alternating, new niche dimensions arise
factors influencing biodiversity: Temporal fluctuations
caused by external influences like seasons, weather, climate; or endogenous processes like predator-prey cycles; change competitive relationships, create new niche dimensions trough adaption
factors influencing biodiversity: spatial heterogeneity
spatial heterogeneity and unequal access to resources: gradients in resource availability, resource concentration can differ on very small spatial scales → strong building of niches
factors influencing biodiversity: Patchiness
metapopulation dynamics or source-sink-dynamics; regional coexistence, while local competitive exclusion; migration inhibits extinction
factors influencing biodiversity: Insular biogeography
Insular biogeography (on near and big islands – highest diversity)
factors influencing biodiversity: seed dormancy
Seed dormancy, can raise diversity, because of the outlast of bad periods, resettlement after extinction
factors influencing biodiversity: predation
Predation can increase diversity (parasitism) or decrease it (predator-mediated completion, intraguild predation)
Why do we find typically a unimodal relationship between the productivity of a habitat (e.g. determined by nutrient concentrations, precipitation) and biodiversity but a saturating function between production (of new biomass) and biodiversity?
Different objects: productivity (=characteristic of the habitat, says how great the production could be) and production (= characteristic of the community, rate of C/energy is fixed, or new biomass is built over time)
Different scales: In experiments we measure the production, there is a positive relationship between biomass production and diversity (complementary mechanism, dominance mechanism and facilitation → overyielding)
Observation of the productivity over different locations get averaged
Different dependency: experiments – total production depends on diversity
observations - diversity depends on abiotic factors and the competition relationships
long story short: they are different things
Unimodal relation between productivity and biodiversity because: with medium productivity the diversity is the highest, because different species are limited by different resources (e.g. Tilman model)
Saturating function between production and biodiversity because: Stability of ecosystem function increases with diversity, at first linear, then weaker → high biodiversity → low variability of ecosystem functions
