At each life stage, organisms require different habitats. In order to maximize survival, there should exist a selective pressure on organisms to choose between high and low quality habitats. This concept of selecting sites to optimize fitness is known as the preference-performance hypothesis. Selective pressure should be greatest on adults when choosing an oviposition site as this decision impacts subsequent life stages and ultimately parental fitness. My study focuses on what habitat variables Rana aurora (Northern Red-legged Frog) select when choosing a high quality oviposition site. To determine this, I am asking two main questions: 1) what abiotic/biotic habitat variables predict the presence/absence of egg masses? and 2) at sites where R. aurora is known to oviposit, what variables impact the total number of egg masses? This study took place at 30 ponds across northern Humboldt County, California. Ponds were visited weekly for five months and the number of eggs deposited was recorded. The abiotic habitat characteristics assessed were water temperature, pH, salinity, dissolved oxygen, and pond area. The biotic factors were average percent canopy cover, emergent vegetation, floating vegetation, woody vegetation, and presence/absence of predators (e.g., fish).
Results/Conclusions:
Ponds with high amounts woody vegetation and high canopy cover contained lower number of egg masses. Frogs did not choose ponds with high amounts of canopy cover because trees block light which, decreases algal growth, the primary food sources for tadpoles. In ponds containing egg masses, higher percentages of emergent and floating vegetation led to more egg masses. Rana aurora attach their egg masses to emergent vegetation and tadpoles use this vegetation for shelter. Therefore, a high quality oviposition site for R. aurora is one that has high amounts of food and shelter for tadpoles. Although this study does not address the performance of the offspring or parental fitness, future studies can determine the performance of R. aurora using these results.
