Lambir lizard and insect abundance project (proposal)

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Nocturnal Lizard and Insect Abundance in a Lowland Mixed Dipterocarp Forest

Background

Large lizard we found -- Gonocephalus grandis.
Lizards and geckos (which here we refer to as “lizards”) are an important part of the rainforest ecosystem, playing a role as both predators and prey to many other animals. Their habitats are wide-ranging, varying from human dwellings to disturbed areas to riparian areas to primary forest. They feed primarily upon small insects and arachnids, such as ants, grasshoppers, and spiders, and occasionally feed upon other geckos.

Question

Knowing what lizards feed upon, is there a correlation between areas in which they can be found nocturnally and the amount of insect abundance found in that area?

Hypothesis

We hypothesize that areas in which lizards have been nocturnally observed will have higher insect abundance than similar areas in which lizards have not been observed. (Here we are making a few assumptions: 1) that the distribution of lizards is not continuous throughout the forest; 2) that they feed mostly upon shrub- and bark-dwelling insects.)

We also hypothesize, as a specification of the primary hypothesis, that areas in which lizards have been observed will have higher ant (Hymenoptera), spider (Arachnida), and grasshopper (Orthoptera) abundances than areas in which lizards have not been observed.

Methods

We will conduct our experiment in this way:

  • We will go out into the field from 2300 to 2400 on two nights (8/6/2010 and 10/6/2010) on the main trail and look for lizards. We will mark the habitats of any that we find with a 2m x 2m plot, observe, and attempt to photograph the animal.
  • In addition to the lizard-observed plots, we will also randomly choose an equal number of trees upon which no lizards were observed and perform the same process and collect the insects. The same number of non-lizard trees as lizard trees will be tested during the daytime and during the night. We will use a random method to determine these sites. Random numbers will be generated to determine the number of steps taken into the forest to the plot from the beginning of the trail, and whether the number is even or odd will determine the left or right side of the trail. The 2m by 2m area directly in front of the walker off the trail will be the area for sampling, assuming the site is sufficiently similar to sites where lizards were found (brush, small saplings, and trees present) and not within 5 meters of another site.
  • We will return to the spots of the night-time observed lizards at night (2300 to 0000) on two nights (8/6/2010 and 10/6/2010) to test for insects. We will sweep with a large butterfly net in an area of 2m x 2m for 16 sweeps through the brush and small saplings, a modification of the method used by in a 2002 paper by NS Sodhi. We will sweep from 1m high to the ground level. We will repeat the process twice at each site and collect the insects from each site. We will also visit the sites in the same order each night, resulting in approximately the same time to visit each.
  • We will count the insects from each site as well as identify them to order.

Analysis

We will analyze our results in this way: We will use the statistics program R to analyze our data and to look for patterns between lizard presence or absence and the abundance of insects (and specifically insect order). We will use a glm (general linear model) to analyze the data. We will look for the significance of rough insect abundance in correlation with lizards, then examine the significance of Hymenoptera (ants), Arachnida, and Orthoptera abundances in correlation with lizards.

If we get significant results, we will be able to say that the two factors are correlated. It would be especially interesting to see if there is a correlation between the lizards and one or more orders of insects. Whether the lizard presence is a direct result of higher insect abundance is a question that would need to be the subject of further study, but our result might suggest such.

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