Resource acquisition by societies part 3

Question 1

How do we evaluate the diversity and patterns of resource acquisition and its consequences?

Answer 1

1. Defining what species eat.
2. Establishing how much species eat.
3. Direct and indirect ecological impacts of what species eat.

Question 2

defining what species eat - define trophic level

Answer 2

Different points on the feeding chain of consumer-resource feeding relationships

Question 3

defining what species eat - define primary producers

Answer 3

The plants and other autotrophs (self-feeding, photosynthetic organisms) that form the base of the feeding chain.

Question 4

defining what species eat - define primary consumers

Answer 4

Consumers of primary producers - herbivores

Question 5

defining what species eat - define secondary consumers

Answer 5

Consumers of primary consumers - carnivores

Question 6

defining what species eat - define top predator

Answer 6

• A predator residing at the top of a food chain, upon which no other species preys
• trophic role dominated by societies.

Question 7

social primary consumer examples

Answer 7

• Leaf-cutter ants
• Many mammal societies (like the mole rats)

Question 8

social top predators examples

Answer 8

• wolves
• social cats (cheetah, lion)

Question 9

How do we determine trophic level?

Answer 9

• direct observations
• waste products
• tissue in organisms
• stable isotope analysis

Question 10

how do we determine trophic level? - direct observations

Answer 10

For simple trophic levels, direct observations can be useful but are often misleading.

Question 11

how do we determine trophic level? - waste products

Answer 11

can look at waste products (feces, etc.), but this is only a “snapshot”

Question 12

how do we determine trophic level? - tissue in organisms

Answer 12

Foods leave detectable traces in the tissues of the organisms that feed on them.

Question 13

how do we determine trophic levels? - stable isotope analysis

Answer 13

Stable isotope analysis is a powerful tool for studying trophic levels of organisms

Question 14

stable isotope analysis - ratio of different isotopes can tell us what?

Answer 14

The ratio of a different isotopes in the tissues of an organism can therefore tell us at which trophic level they have been feeding

Question 15

stable isotope analysis - nitrogen and carbon ratios

Answer 15

• 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.

Question 16

stable isotope analysis in ants

Answer 16

• lower ratio = herbivory
• higher ratio = predation/scavenging

Question 17

Examples of complexities in trophic interactions that stable isotopes can address

Answer 17

• Variability in diet of species within a species
• Geographical variations
• Contrasts between recovering and mature habitat.
• Contrasts across urban and natural environments

Question 18

Examples of complexities in trophic interactions that stable isotopes can address - variability in diet of species

Answer 18

stable isotopes can address differentiating trophic differences in cryptic feeders.

Question 19

Examples of complexities in trophic interactions that stable isotopes can address - geographical variation

Answer 19

stable isotopes can link the differences in diet to patterns of environmental shifts.

Question 20

Stable isotope example

Answer 20

Variation in diet across habitats in Chimpanzees

Question 21

stable isotope example - variation in diet across habitats in Chimpanzees

Answer 21

• Stable isotopes reveal substantial differences in diet across sites
• explained by complex interactions between habitat, and access to different ratios of food types.

Question 22

establishing how much species eat - what is the only way to determine precise biomass consumption

Answer 22

Direct measurements of feeding are the only way to determine precise biomass consumption.

Question 23

establishing how much species eat - what is the focus typically on?

Answer 23

the focus is on feeding rates within some logistically feasible observation window

Question 24

establishing how much species eat - Rate data can then be combined with other data types to calculate total biomass consumption. e.g. using:

Answer 24

• Daily foraging period.
• Annual activity pattern.
• Size of society.
• Size of population.

Question 25

establishing how much species eat - what can provide an alternative to feeding rates

Answer 25

Indirect measures of food/prey depletion can provide a viable alternative.

Question 26

establishing how much species eat - Direct measure example

Answer 26

Leaf-cutting ant leaf consumption

Question 27

establishing how much species eat - Indirect measure example

Answer 27

Impact of army ants on arthropod communities

Question 28

Impact of army ants on arthropod communities - how is this assessed?

Answer 28

Impact of two army ant species assessed by before/after measures of prey size, density, and biomass.

Question 29

Defining a food web - how do we further break down trophic levels

Answer 29

can further break down trophic levels into guilds

Question 30

defining a food web - define guilds

Answer 30

a group of species that occupy a similar trophic role within a trophic level

Question 31

defining a food web - all connections are drawn between what?

Answer 31

All existing connections are drawn between all consumer and resource species

Question 32

defining a food web - what makes it more complex?

Answer 32

The more feeding links each species has, the more complex the food web becomes

Question 33

defining a food web - overall food complexity can be described by what?

Answer 33

Overall food web complexity can be described by the number of feeding links and the number of trophic levels and guilds.

Question 34

defining a food web - what increases with the number of trophic levels?

Answer 34

Number of trophic levels increases with species richness - creating more complex food webs.

Question 35

Food web complexity - more species, guilds, and total interactions

Answer 35

Adding species and guilds increases complexity (links) even when each species is involved in a similar number of interactions

Question 36

Food web complexity - omnivory and more trophic links

Answer 36

• Additional food web complexity also comes from more feeding interactions
• which is typically achieved via omnivory, often among guilds.

Question 37

define top-down control

Answer 37

When a higher trophic level controls the size of the trophic level below it.

Question 38

define bottom-up control

Answer 38

When the size of a trophic level is determined by the rate of production of its resources

Question 39

define trophic cascade

Answer 39

When the indirect effects of consumer resource interactions extend through other trophic levels

Question 40

Disproportionate impacts within the food web - bottom-up control

Answer 40

Increased production results in greater productivity at all higher trophic levels

Question 41

disproportionate impacts within the food web - top-down control

Answer 41

Consumers depress the trophic level on which they feed, indirectly increasing the next lower trophic level

Question 42

disproportionate impacts within the food web - addition of a fourth trophic level

Answer 42

• Results in a trophic cascade linking all the trophic levels in a community
• Relative biomass of trophic levels alternative

Question 43

Loss of top-down control in a tropical food dominated by social herbivores and predators

Answer 43

• 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