Invasive species often cause direct and indirect effects on native fauna and flora.  The arrival of brown tree snakes in Guam has become a classic example of the impact that invasive species can have on native birds.  In this example, pythons may be having an indirect effect on the success of fresh-water turtle nests.  The artificial nests showed that the more mammal observations per camera, the greater the number of predation events.  This suggests that the presence of mammals results in predation of turtle nests.  Predation of nest sites was lowest where pythons have been present for the longest time (which suggests the population size of the pythons will be highest) and highest where pythons are not yet confirmed to be present.  This suggests an indirect effect of an invasive species on native mammals which in turn allows a native reptile to reproduce more successfully.  Whilst initially this might seem beneficial (assuming we place a greater value on turtles than mammals) but there could be further indirect effects (eg in the food source of turtles which might now be grazed to a greater amount).  This could have further indirect effects not yet considered or measured.  Pythons could also be having further indirect effects on other groups of species.

The moth Achyra rantalis feeds on Sesuvium portulacastrum on islands in the Bahamas. The lizard Anolis sagrei is present on some islands and will consume Achyra. These areas are highly susceptible to disturbance from hurricanes. Hurricanes can also affect this system: Hurricane Frances had a bigger storm surge than Mitch, Floyd and Michelle.  In addition, longer periods of warm dry weather can initiate moth outbreaks on islands without lizards.

Describe the interactions between moths, Sesuvium, lizards and the weather.

Source: Spiller et al. 2016. Ecology, 97: 2540-2546

Figure 2 reproduced with permission of John Wiley & Sons.

© 2016 by the Ecological Society of America.

Arctic fox dens around Hudson’s Bay were surveyed to record plants growing there, snow thickness and presence or absence of lemming nests.  Foxes need dens that are deep enough to shelter families through the winter but without having to excavate into permafrost.  Dens are usually well established and continue to be used over long periods of time.  Areas around dens tend to have more nutrient-rich vegetation due to deposition of faeces and urine and show up as more lush green vegetation of Leymus mollis and Salix planifolia  compared with surrounding tundra, dominated by very low-growing Dryas integrifolia.  The shrubby vegetation growing around fox dens traps a deep layer of snow.  What do the results from this experimental work show?

Source: Gharajehdaghipour & Roth, 2018. Ecosphere, 9: https://doi.org/10.1002/ecs2.2077

Figures reproduced under the terms of the Creative Commons Attribution License (CC-BY)

http://www.wileyopenaccess.com/details/content/12f25db4c87/Copyright–License.html

In shallow subtitle habitats on the west coast of the US, the señorita (Oxyjulis californica) is a common fish that eats small molluscs and crustaceans found in feather boa kelp forests (Egregia menziesii).  Molluscs such as the limpet Lottia insessa feed on the kelp.  Haggerty et al (2018) ran a series of experiments to understand these interactions.  They looked at ‘consumptive effect’ by excluding señorita and removing limpets daily by hand; ‘non-consumptive effect’ was tested by allowing señorita to be present but not to eat limpets on the kelp; the ‘total predator effect’ was tested by allowing señorita full access to kelp to predate limpets.  The ‘predator control’ treatment allowed limpets access to kelp and señorita were excluded.  Grazing scars and tissue loss were assumed to be good indicators of the impact of limpet grazing. Interpret the results shown in figures (a) and (b).  Bars with a different letter are significantly different from each other.

Source: Haggerty et al. 2018. Ecology, 99: 1574-1583

Figures reproduced with permission of John Wiley & Sons.

© 2018 by the Ecological Society of America.

Pepi et al (2018) investigated the impact of raised temperature on predation of tiger moth caterpillars (Arctia virginalis) and a predatory ant (Formica lasioides) in a 3-day experiment.  The graphs here show the results from two trials at different temperatures (x-axis shows number of ants in each treatment; blue = warming; red = control; size of circles isn’t relevant for this question) comparing the survival of caterpillars and ants.  What do these results mean and what broader impacts might this have?

For extra credit: what affect could temperature be having on metabolism and growth of these insects?  Larger caterpillars are less vulnerable to predation –does this fit into the picture here, and if so, how?

Source: Pepi et al. 2018.  Ecology, 99: 1584-1590

Figure reproduced with permission of John Wiley & Sons

© 2018 by the Ecological Society of America.