Download Rocky Intertidal Lab Questions – 2006

Rocky Intertidal Lab Questions – 2006
As you learned so well in Marine Ecology (Bio 160), the rocky intertidal environment has
attracted the best and the brightest of ecologists fascinated by the marked zonation of species
occurrences across the gradient of tidal heights. This compressed zonation of species has allowed
ecologists to very efficiently test hypotheses posed to explain what environmental and biological
processes are responsible for determining the upper and lower boundaries of species ranges. By
extension, ecologists have examined the ecological processes responsible for spatial variation in
community attributes, including species composition and relative abundance, as well as species
richness and diversity. As described in the handout for this lab, the purpose of this lab is to
introduce you to the diversity of algae and invertebrates that inhabit the rocky intertidal, expose
you to these remarkable patterns of zonation, and learn some of the common methods ecologists
use to quantitatively describe the distribution and abundance of species in this habitat. In
particular, by using two different spatial sampling designs to estimate the relative cover of
species across the intertidal gradient (linear transects vs. 2-dimensional quadrats), we can
examine how well the patterns generated by these methods agree with one another. Therefore
using these two sampling methods we pose the following questions:
1) How well do the patterns of abundance (percent cover) of common macroalgae and
sessile invertebrates generated by the linear point intercept and the quadrat point intercept
methods compare with one another? For each section of the linear transect across the
tidal gradient and the quadrats included within each of those sections, how would you
plot a species abundance to test how well the two measures correspond with one another?
2) How well do the estimates of species richness (i.e. number of species) generated by these
two methods compare both across the entire intertidal range and within each of four
segments from low to high tidal levels?
3) How do the descriptions of the macroalgae and invertebrate assemblages (i.e. relative
abundance of common species) differ among these two sampling methods across the
entire gradient and within each of four segments from low to high tidal levels?
4) Based on the above results, what can you say about how different spatial sampling
designs (i.e. linear vs. 2-dimensional) influence your description of the intertidal
community?
5) What attributes of species might explain why they are distributed the way they are?
6) Based on the above results, can you predict what section of the intertidal Yuri would
choose to sunbathe in and why?