Predator-prey interactions and changing environments: who benefits?

Abstract

While aquatic environments have long been thought to be more moderate environments than their terrestrial cousins, environmental data demonstrate that for some systems this is not so. Numerous important environmental parameters can fluctuate dramatically, notably dissolved oxygen, turbidity and temperature. The roles of dissolved oxygen and turbidity on predator-prey interactions have been discussed in detail elsewhere within this issue and will be considered only briefly here. Here, we will focus primarily on the role of temperature and its potential impact upon predator-prey interactions. Two key properties are of particular note. For temperate aquatic ecosystems, all piscine and invertebrate piscivores and their prey are ectothermic. They will therefore be subject to energetic demands that are significantly affected by environmental temperature. Furthermore, the physical properties of water, particularly its high thermal conductivity, mean that thermal microenvironments will not exist so that fine-scale habitat movements will not be an option for dealing with changing water temperature in lentic environments. Unfortunately, there has been little experimental analysis of the role of temperature on such predator-prey interactions, so we will instead focus on theoretical work, indicating that potential implications associated with thermal change are unlikely to be straightforward and may present a greater threat to predators than to their prey. Specifically, we demonstrate that changes in the thermal environment can result in a net benefit to cold-adapted species through the mechanism of predator-prey interactions.

Figure 1

Dissolved oxygen levels (mg l⁻¹) measured 10 cm above the substrate in Delta marsh, located at the south end of Lake Manitoba.

Figure 2

Turbidity (measured in NTUs) measured 10 cm above the substrate in Delta marsh, located at the south end of Lake Manitoba.

Figure 3

Temperature measured 10 cm above the substrate in Delta marsh, located at the south end of Lake Manitoba.

Figure 4

Satellite image (June 2005) of the north basin of Lake Winnipeg illustrating the pattern of turbid water throughout the basin.

Figure 5

The time until loss of equilibrium for fathead minnows and yellow perch exposed to four different dissolved oxygen environments. Results illustrate the mean±1 s.e. The maximum time available within the apparatus is 360 min. From Robb & Abrahams (2003) and reproduced with permission from Blackwell Publishing.

Figure 6

The effect of a warming environment on (a) the trout population and (b) the ferox trout population. The horizontal axis corresponds to the population size when there is no change in temperature and the vertical axis represents the population size with increased temperatures. The coordinates for this plot are the corresponding points for both conditions over a 75-year period (years 26–101). If the data lie above the diagonal (x=y), then increasing temperatures increase population size. If the data fall below this line, populations decline in response to global warming. Data that fall around the diagonal indicate no influence of global climate change. Open circle and filled triangle correspond to an increase of 3 and 7°C, respectively.

Figure 7

The effect of a warming environment on (a) the charr population and (b) the piscivorous charr population. These plots and their interpretation are the same as for figure 6.