Discussion Question
- Schmitz (1998) found that trait-mediated indirect interactions (TMII) were stronger than density-mediated indirect interactions (DMII) in a spider-grasshopper-grass system. Rinehart et al. (2017) ran a similar experiment with ladybeetles (predator) – scale insects – cordgrass .
The plot shows the density of the prey over time. Does it show evidence for a trait-mediated effect of ladybeetles, density-mediated effect of ladybeetles, both, or neither? Briefly explain.
- The right plot shows the biomass of the resource (cordgrass) in each treatment. Does it show evidence for a trait-mediated effect of ladybeetles, density-mediated effect of ladybeetles, both, or neither? Briefly explain.
- We discussed the regime shift in the North Atlantic following the crash in cod populations in the 1980s. Hanson et al. (2018) quantified the stable isotopes in seal teeth to make inferences on their diet. The plot below shows the 15N and 13C ratios for teeth collected from seals in 1970 and others from seals collected in 2005 . Based on these data, how has the collapse of cod affected the trophic position of gray seals?
- (a) Calculate the Shannon index (H’) and Chao’s estimator for Species Richness for each of these three samples.
Species
Com 1
Com 2
Com 3
A
2
40
170
B
1
40
5
C
1
30
5
D
1
30
5
E
1
20
5
F
0
0
5
Shannon
Index (H’)
Richness with Chao estimate
(b) Form an argument why each of the three communities might be considered the most “diverse.”
Com 1:
Com 2:
Com 3:
- Here are the taxa found in four forest litter samples in 2019.
AS-1-O
DO-2-O
EH-2-O
TP-3-C
Annelid Earthworm
Annelid Earthworm
Beetle cloverstem borer
Annelid Earthworm
Ant rover
Sowbug
Beetle grub hairy
Snail brown
Beetle cloverstem borer
Spider wolf
Cricket house
Sowbug
Sowbug
termite
What is the mean α richness for these samples?
What is the γ richness of these four samples?
What is the β richness among these samples?
- Use these richness values to explain, in plain English, how the diversity within these samples compares to the diversity among them. Are they more similar or more different? Remember our discussion of Chase (2003)— β diversity represents the dissimilarity between samples.
- A colleague returns from a trip to two islands in the South Pacific with a broad grin on her face. “I’ve disproved McArthur and Wilson’s model of island biogeography! My data show that the small island had more species than the larger one.”
(a) The plot below has extinction curves for large and small islands. Add colonization curves that would show how a smaller island (A2) could have more species at equilibrium than a larger one (A1). Label which island each curve applies to.
(b) From your drawing, which island (A1 or A2) would have a higher turnover rate (change in species identity over time)? Why?
