# Presentation notes

- There were 3 major findings obtained over the course of the 5 year study. These will be explained using the graphical represntations for each finidng provided in the paper.

## Slide 1

- Shown here is a phase plot of the **mean population density** of the larger D. spectabilis vs. that of the medium sized Dipodomys species.

- The plot has vectors that point towards the shift in densities from the start to the end of the study period.

- The primary finding was that densities of D. spectabilis increased on seed addition plots in an inversely proportional manner to that of D. merriami and D. ordii. These shifts occured in both control and experimentally induced conditions. This indicates the presence of a strong competitive relationship between D. spectabilis and the medium-sized Dipodomys species.

## Slide 2

- These plots depict the energy consumed by various rodent species on experimental plots with fence gates closed vs. fence gates opened. The legend for the plots is as shown here. The dotted line represents equal consumption of energy in both scenarios.
- In these plots, energy consumption by the rodents with the gates opened is generally higher as there is greater chance of encountering food. However, the plot depicting the energy consumed by small seedeaters stands out, as their energy consumption is not affected by the gates being open or closed. The presence of D. spectabilis on the seed addition plots appears to have prevented the establishment of residences by the small seedeater. This is due to the high energy consumption of D. spectabilis which fuelled an increase in its population densities.

## Slide 3

- This plot shows the changes in population densities of the Dipodomys species, small seedeaters and other non-granivorous rodent species over the study period.
- The data was collected on 4 experimental and 4 control plots and has been subsequently constrasted.The dark dots represent the control plots, while the hollow dots represent the experimental plots with the Dipdomys species removed.
- The topmost plot depicts erratic changes in mean population densities in the control plots for Dipdomys species. Under the eperimental condition, the populations of all Dipodomys species quickly became non-existent.
- The next plot shows that the small seedeaters, which hadn't responded to the removal of D. spectabilis alone, increased several-fold with the removal of all 3 Dipdomys species. This indicates a strong competitive effect of the medium sized Dipodomys species on the small granviorous rodents.
- The final plot shows no changes in the densities of non-granvorous rodents in both experimental and control settings.

## Discussion

- The study identified that limited food availability and interspecific competition are significant to the population densities and organisation of the desert rodent community.

- As shown in the phase plots earlier, the direction of the reciprocal density shifts between medium-sized and large-sized Dipodomys species is highly dependent on seed availability.

- Despite densities of non-resident medium-sized rodent species being high on plots with high densities of D. spectabilies due to greater food availability, these species are inhibited from establishing permanent residence by D. spectabilis, indicating strong interspecific competition.

- With the removal of all 3 Dipodomys species, the population density of small seedeaters greatly increased, while non granivorous rodents did not respond to this treatment. This indicates that grain availability was not a limiting factor influencing non granivorous population densities.

- Removal of all granivorous rodents caused annual large-seeded winter plants to increase several thousand-fold in population.

## Limitations

The study has several limitations.

- Firstly, the partitioning of resources among different rodent species was not accounted for. Complex interacting factors such as regulation of populations via interspecific interactions and biological traits of species were not studied in enough detail, thereby failing to provide adequate insight into how food resources are distributed.

- Next, there is a lack of compensatory responses by the species in the ecosystem for the energy being consumed. This occurs due to aggression between members of the same species, interspecific competition with other seedeating organisms in the ecosystems, and risk of predation by lizards, birds, etc. which impose constraints on foraging.

- How any given species in an ecosystem competes with another is not independent of their biological characteristics such as size differences and aggressive behaviours. Asymmetric competition that arises out of such factors produced noncomplemntary results in the study. For instance, the medium sized Dipodomys species greatly influenced the population densities of the small granivorous rodents, but these small granvioous rodents were unable to influence the population densities of the medium-sized Dipodomys species. The lack of reciprocity in these density shifts rose from asymmetrical competition.

- There were long delays in rodent response to experimental manipulations. This occured due to the dependence of these responses on favorable climate conditions and time of the day, which are required for rodent reproduction and adequate availability of seeds.

That's it i'm outta here