ecology 6 to 9 Flashcards
how do we describe communities?
community structure:
- describes which organisms are present in a given
environment, in what numbers, and how they relate to each other
what is a food-web?
A graphical representation of feeding relationships in a community (show trophic connections)
what is omnivory?
feeding on more than one trophic level
what is a food chain?
a single energy pathway within a food web
how do you calculate the trophic level of an organism?
- for non-omnivores, start with 1 for primary producers then add a number for every level you go up
- for omnivores, the sum of the trophic position of pathway*proportion of diet
how much energy is transferred to the next trophic level?
10% (so 90% is lost)
how do we know about feeding relationships?
- direct observation (but chances are very low to observe it)
- gut or stomach content analysis (but this only shows recent diet)
- stable isotope analysis of tissue (+3% 15N for every trophic level)
what are the different ways food webs can be represented?
- connectence web
- energy web
- interaction web
what is connectedness?
a description of how “linky” a food web is (=mean number of links per species)
what is food chain length?
the number of links from top to basal species (describes how long a food web is)
what are the two hypotheses that limit food chain length?
- energetic hypothesis
- the productive-space hypothesis
what is the energetics hypothesis?
length is limited by inefficient transfer of energy
what is the productive-space hypothesis?
larger ecosystems harbor longer food chains
which species are important in an ecosystem?
keystone species
what is a keystone species?
a species whose removal has larger effects on many other species in a community, disproportionate to its abundance
what are the various types of keystone species?
- major predators
- unique food source ( e.g. unique and limited tree species)
- ecosystem engineer (e.g. beaver)
what is the difference between a dominate and a keystone species?
- highly abundant species (dominant) have a large effect due to their high numbers but are not necessarily keystone (effect is proportional to their abundance)
what is a direct and an indirect interaction?
- direct: the direct effect of one species on another
- indirect: occur when the effect of one species on another is mediated by a third species
what is exploitive competition?
two species that share a common food resource may be in exploitative competition (=competing for a limited resource)
which type of interaction is mutualism?
positive for both species
what is apparent competition?
Two species who share a natural enemy (two producers that share a consumer)
what is a trophic cascade?
indirect effects across two or more species
what is top-down control vs bottom-up control?
- top-down: Postulates predators control herbivores, and herbivores control producers (=cascade down)
- bottom-down: Postulates plants control herbivores, and herbivores control predators (= cascade up)
how can you determine whether a trophic cascade is top-down or bottom-up control?
do an experiment where you can: remove a predator, add a predator, and/or add nutrient
what is wasp-waist control?
where there is an upwards and a downwards effect when changing something in the middle of a cascade
what is an ecosystem?
a biological community plus all the biotic factors influencing that community; study the flow of energy and the cycling of materials in ecosystems
what is primary production?
autotrophs, or “self-feeding” organisms, that make their own organic molecules from carbon
dioxide.
what is primary productivity?
the rate at which energy is converted to plant biomass (expressed as the rate of biomass formation per unit time and space OR rate of energy capture per unit time and space)
what is net primary productivity?
= Gross primary production (energy or carbon fixed via photosynthesis per time) - energy (or carbon) lost via respiration per time
what is a way to measure primary productivity?
Gas exchange in the light vs. gas exchange in the dark
what is the difference between production and stock?
- production: rate of energy or biomass
- stock: amount of energy stored or biomass
why is it that net primary production varies with different biomes?
- Primary production requires a continuous supply of nutrients, such as N, P, Fe, in order to proceed
- differences in temperatures, sunlight, and water (moisture)
which nutrients are often the limiting factor for primary production?
- Nitrogen: needed for chlorophyll and amino acids
- Phosphorus: crucial for photosynthesis, and built into DNA and membranes
- Micronutrients: e.g. Iron (in the ocean). Required for the synthesis of chlorophyll, several photosynthetic electron transport proteins
in the ocean, what is the limiting nutrient for phytoplankton primary production?
nitrogen
what is Liebig’s Law of the minimum?
The rate of any biological process is limited by the factor that is in least amount relative to the organisms’ requirements
what are the differences to the limits to primary production on land and in water?
- water: usually depends on the rate at which the limiting nutrient is added to the system. Highest along continental margins and upwelling regions that bring nutrients to the surface. In addition, there is a strong dependence on light and growing season length
- land: variations in temperature and moisture can account for the differences in primary production. Nutrient availability also has a measurable influence.
what is secondary production?
the formation of living mass of a heterotrophic population or group of populations over some period of time
what is basal metabolic rate and how is it affected by the body mass of the species?
- The amount of energy expended by an animal at rest in a neutral temperature
- increases proportional to body mass
The Earth is an ____ system with respect to energy input (energy is constantly supplied by the sun).
The Earth is a _______ system with respect to nutrient input (ignoring the periodic bombardment by material from outer space)
- open
- closed
what is fast carbon vis slow carbon?
- Fast carbon-> plants grow, make sugar, feed animals.
- Slow carbon-> chemical reactions and tectonic activity, carbon takes between 100-200 million years to move between rocks, soil, ocean, and atmosphere
- the whole cycle is in dynamic equilibrium
what is the effect of humans on the carbon cycle?
- Humans are very efficient at moving carbon from earth to the atmosphere.
- Since the industrial revolution, we have started and increased the rate at which we use (and emit) slow carbon
- More carbon in the atmosphere is not being recycled down at the same rate (we are quickly releasing slow carbon)
what is biogeography?
the study of distributions of organisms
across space
what are ecoregions?
large units defined by plant/animal distributions
what makes up the distribution of plants? (Factors that affect distribution)
precipitation, soil, sunlight, temperature
ecoregions are usually defined by what?
plants
what is species distribution and what are the different scales?
- describes the area occupied by a population or species
- global, regional, landscape
what does the global scale of species distribution represent?
species range
are most species ranges big or small?
larger-ranging species have larger local abundance
what factors can limit species distribution?
- A species requires a certain abiotic habitat to persist as a viable population (Abiotic factors)
- Species have different ways to disperse across the landscape, and may not reach all suitable habitats. (Dispersal limitation)
- Even if they can get there, species may be limited by competition, or lack of facilitators. (Biotic factors)
how can an experiment help determine drivers of range limits?
Transplant experiments can decipher range limiting mechanism:
- Transplant successful: Distribution limited either because the area is inaccessible, time has been too short to reach the area, or because the species fails to recognize the area as suitable living space
- Transplant unsuccessful: Distribution limited either by other species or by physical and chemical factors
what are the three main models for understanding dispersal?
- Diffusion
- Jump dispersal- movement of individuals across large distances (usually inhospitable terrain) – accelerated by humans
- Secular dispersal - diffusion over evolutionary time scales
what are establishment or spread rates driven by?
not driven by mean dispersal distances but by extreme dispersal
in islands, what determines how many species are present?
the area – larger areas will have more species
what explains the species-area relationship among islands?
- Since larger areas hold more individuals, and extinction is less likely in large populations, extinction is lower on larger islands.
- Target effect: larger islands have a larger shoreline, which leads to higher immigration rates (higher chance of intercepting dispersing individuals).
- Higher geographic/habitat diversity on larger islands (e.g., elevation, precipitation).
- More evolutionary diversification on larger islands (more opportunity for local adaptation within-islands).
what is the isolation effect?
- fewer species on more isolated islands
what is the Equilibrium Theory of Island Biogeography?
- Number of species on islands is an equilibrium between arrival and local extinction
- On larger islands, there is a lower rate of extinction
- On more isolated islands, there is a lower rate of immigration
