A biologist observes that a species of beetle is abundant under logs in the forest but is rarely observed in any other location.
(a) Identify THREE variables (two abiotic and one biotic) that might explain why these beetles are found under logs much more frequently than anywhere else.
(b) Using one of the factors listed in part (a) as an independent variable, write a hypothesis that proposes how this variable could cause the beetles to be found more frequently under logs.
(c) Design a procedure for a controlled experiment to test your hypothesis.
(d) Describe the results that would support your proposed hypothesis, and the results that would refute your hypothesis.
- JazSincLv 72 weeks agoFavorite Answer
i. it's dark (abiotic)
ii. it's humid (abiotic)
iii. it's enclosed - the beetle may like having both its top and bottom surfaces touching something (abiotic)
iv. other beetles of the same species are there (biotic)
v. food is there, i.e. they eat the wood (biotic)
b) illumination ("it's dark")
My hypothesis is that these beetles are nocturnal. I could speculate that nocturnal beetles would be less likely to be eaten by diurnal birds.
c) I built an extended "T maze" in which one end of the T was illuminated and the other end of the T was as dark as I could get it. Conditions in the maze ends were otherwise the same. The humidity and temperature were held at the same as I found in the preferred logs in their natural forest setting. The maze was thoroughly cleaned between runs to prevent accumulation of pheromones. Runs were performed with individual beetles.
d) My experiment may be poorly designed. I ran the idea past some colleagues over lunch. They asked me what I would do about beetles that did not end up in either end of the T. Since those areas are illuminated, I decided to count the problematic beetles as wins for "illumination OK." I also decided to put a small bit of wood, but not big enough to hide under at both ends of the T, just in case that was food, to encourage a beetle to stay at an end of the T.
Results that would support my hypothesis: a much greater number of beetles would stay at the dark end than stayed in the bright end + anywhere else illuminated in the maze.
Results that would refute my hypothesis: beetles randomly chose which end to come to rest.