Resource acquisition by societies part 3 Flashcards
How do we evaluate the diversity and patterns of resource acquisition and its consequences?
- Defining what species eat.
- Establishing how much species eat.
- Direct and indirect ecological impacts of what species eat.
defining what species eat - define trophic level
Different points on the feeding chain of consumer-resource feeding relationships
defining what species eat - define primary producers
The plants and other autotrophs (self-feeding, photosynthetic organisms) that form the base of the feeding chain.
defining what species eat - define primary consumers
Consumers of primary producers - herbivores
defining what species eat - define secondary consumers
Consumers of primary consumers - carnivores
defining what species eat - define top predator
- A predator residing at the top of a food chain, upon which no other species preys
- trophic role dominated by societies.
social primary consumer examples
- Leaf-cutter ants
- Many mammal societies (like the mole rats)
social top predators examples
- wolves
- social cats (cheetah, lion)
How do we determine trophic level?
- direct observations
- waste products
- tissue in organisms
- stable isotope analysis
how do we determine trophic level? - direct observations
For simple trophic levels, direct observations can be useful but are often misleading.
how do we determine trophic level? - waste products
can look at waste products (feces, etc.), but this is only a “snapshot”
how do we determine trophic level? - tissue in organisms
Foods leave detectable traces in the tissues of the organisms that feed on them.
how do we determine trophic levels? - stable isotope analysis
Stable isotope analysis is a powerful tool for studying trophic levels of organisms
stable isotope analysis - ratio of different isotopes can tell us what?
The ratio of a different isotopes in the tissues of an organism can therefore tell us at which trophic level they have been feeding
stable isotope analysis - nitrogen and carbon ratios
- Nitrogen (15N vs. 14N) and carbon (13C vs. 12C) ratios are particularly informative
- heavier isotopes (extra neutron) are known to increase predictably with increasing trophic level.
stable isotope analysis in ants
- lower ratio = herbivory
- higher ratio = predation/scavenging
Examples of complexities in trophic interactions that stable isotopes can address
- Variability in diet of species within a species
- Geographical variations
- Contrasts between recovering and mature habitat.
- Contrasts across urban and natural environments
Examples of complexities in trophic interactions that stable isotopes can address - variability in diet of species
stable isotopes can address differentiating trophic differences in cryptic feeders.
Examples of complexities in trophic interactions that stable isotopes can address - geographical variation
stable isotopes can link the differences in diet to patterns of environmental shifts.
Stable isotope example
Variation in diet across habitats in Chimpanzees
stable isotope example - variation in diet across habitats in Chimpanzees
- Stable isotopes reveal substantial differences in diet across sites
- explained by complex interactions between habitat, and access to different ratios of food types.
establishing how much species eat - what is the only way to determine precise biomass consumption
Direct measurements of feeding are the only way to determine precise biomass consumption.
establishing how much species eat - what is the focus typically on?
the focus is on feeding rates within some logistically feasible observation window
establishing how much species eat - Rate data can then be combined with other data types to calculate total biomass consumption. e.g. using:
- Daily foraging period.
- Annual activity pattern.
- Size of society.
- Size of population.
establishing how much species eat - what can provide an alternative to feeding rates
Indirect measures of food/prey depletion can provide a viable alternative.
establishing how much species eat - Direct measure example
Leaf-cutting ant leaf consumption
establishing how much species eat - Indirect measure example
Impact of army ants on arthropod communities
Impact of army ants on arthropod communities - how is this assessed?
Impact of two army ant species assessed by before/after measures of prey size, density, and biomass.
Defining a food web - how do we further break down trophic levels
can further break down trophic levels into guilds
defining a food web - define guilds
a group of species that occupy a similar trophic role within a trophic level
defining a food web - all connections are drawn between what?
All existing connections are drawn between all consumer and resource species
defining a food web - what makes it more complex?
The more feeding links each species has, the more complex the food web becomes
defining a food web - overall food complexity can be described by what?
Overall food web complexity can be described by the number of feeding links and the number of trophic levels and guilds.
defining a food web - what increases with the number of trophic levels?
Number of trophic levels increases with species richness - creating more complex food webs.
Food web complexity - more species, guilds, and total interactions
Adding species and guilds increases complexity (links) even when each species is involved in a similar number of interactions
Food web complexity - omnivory and more trophic links
- Additional food web complexity also comes from more feeding interactions
- which is typically achieved via omnivory, often among guilds.
define top-down control
When a higher trophic level controls the size of the trophic level below it.
define bottom-up control
When the size of a trophic level is determined by the rate of production of its resources
define trophic cascade
When the indirect effects of consumer resource interactions extend through other trophic levels
Disproportionate impacts within the food web - bottom-up control
Increased production results in greater productivity at all higher trophic levels
disproportionate impacts within the food web - top-down control
Consumers depress the trophic level on which they feed, indirectly increasing the next lower trophic level
disproportionate impacts within the food web - addition of a fourth trophic level
- Results in a trophic cascade linking all the trophic levels in a community
- Relative biomass of trophic levels alternative
Loss of top-down control in a tropical food dominated by social herbivores and predators
- The army ant Nomamyrmex esenbeckii is a specialist predator of leaf-cutting ants
- On small, newly formed tropical islands, army ant predators go extinct, and herbivory by leaf-cutting ants sends the islands into “Ecological meltdown”
- leaf-cutter ants eat the islands bare of all vegetation and each island system collapses
