You conduct an experiment to determine the concentration of ions in an unknown solution you place 300ml inside a dialysis bag and place into a beaker of water with an ion concentration of 100 ppm when you check the expierment an hour later the bag is deflated and has lost much of its water

Gravitational force i believe

The rate that would change would be the  searching efficiency/attack rate. there are only two other rates in this model: the  growth rate of prey, and the  predator or consumer mortality rate.the  searching efficiency/attack rate is what indicates how effectively can a predator capture its prey whether in the searching process or actual capturing/attacking process.