Students are also able to point out that their current tropical diversity model is not robust enough, given its reliance on data solely
concerning plants (ectotherms). When asked to verbally propose
an experiment that might help remedy this issue, students typically
offer one to test whether similar patterns are seen among endotherms (such as mammals).
As is often the case in an MBI setting, instructors help guide
student thinking through questioning, discussion, and presenting
new evidence to further develop the explanatory model. Thus, after
working with Wright et al.’s (2006) paper, students examine a
study by Gillman et al. (2009), who researched this phenomenon
using mammals (endotherms). This experiment, too, needs some
elaboration, so students use Worksheet 3 (Appendix D), which
explains how Gillman and colleagues assessed rates of microevolution in 10 orders and 29 families of mammals. Comparisons were
made between 130 sister-species (closely related) pairs, in which
one species occurred at a lower latitude or elevation than the other
species of the pair. The students are prompted by Worksheet 3 to
consider performing some basic calculations for ascertaining patterns in the data. Students can calculate means of branch length
ratios (distance from common ancestors for the tropical species
vs. distance from the common ancestors for the temperate species),
both for organisms overall and for organism subcategories (within
specific orders/families [e.g., Rodentia] or by latitude and by elevation). They will find that the mean value of the ratios is >1, meaning that tropical species or lower-elevation species have higher rates
of molecular evolution than their temperate or higher-elevation
counterparts. Indeed, Gillman et al. (2009) concluded that tropical
mammals have higher rates of molecular evolution than their temperate relatives. On the basis of these data, students are again asked
to revise their models of greater biodiversity in the tropics and offer
thoughts regarding needs for next steps toward a more viable class
model. Discussion is focused on the fact that since mammals are
endotherms, their metabolic rates do not vary with temperature.
Gillman et al.’s (2009) finding that mammals also have higher rates
of molecular evolution in the tropics suggests a model based on the
Red Queen hypothesis, stating that the speed of mammalian evolution is influenced by the evolutionary speed of ectotherms.
After engagement with Gillman et al.’s (2009) data and paper,
as after the Wright et al. (2006) activity, we have found students
able to conclude (as did Gillman and colleagues in 2009) that
they need more data (across additional organisms) to build more
viable models – specifically data concerning other tropical and
temperate taxa. They are given three additional papers to read
and summarize in groups of three (each student reading one article
and reporting to the other two). Each new paper reports on
research that seems to strengthen the empirical consistency of their
developing model, that greater biodiversity in the tropic zones is
ultimately caused by higher rates of mutations per greater solar
energy per area. The papers report findings similar to those of
Gillman et al. (2009) but in plants (Gillman et al., 2010), fishes
(Wright et al., 2011), and amphibians (Wright et al., 2010).
At this point, students are working from a class model that posits
higher mutation rates as one cause of the greater biodiversity in the
tropic zones. Inferred is the mechanism of higher tropical temperatures
causing greater oxidative damage to DNA, on average, resulting in more
mutations and greater genetic “raw material” for subsequent evolutionary processes (like natural selection and genetic drift) to act upon.
Discussion
Modeling-based inquiry is a constructivism-based pedagogy that
allows learners to engage with authentic science practices. Yet many
science educators have not experienced this way of learning and therefore are ill-prepared to teach via MBI (Windschitl, 2008b; Harlow,
2010). Here, we have described a new postsecondary MBI-based curriculum taught to undergraduate university students, including those
aspiring to be K–12 educators. Via class assessments, exit interviews,
and surveys, students demonstrated an increased felt efficacy of participating in and facilitating MBI and scientific modeling overall. They
increased their understanding and their ability to help other learners
engage in scientifically oriented questions based on evidence, develop
and evaluate explanations based on evidence and specifically in light
of new evidence, weigh the worth of competing or alternative explanations, and communicate and justify their evidence-based explanations
(for a more in-depth detailing of these results, see Adumat et al., 2011).
Since the development and last implementation of this curriculum in 2012, various researchers have advanced data that add to the
fascinating story of model building around the latitudinal diversity
gradient. Recent studies suggest that there are other factors in addition
to temperature (e.g., spatial relationships, historical factors, productivity) that have important effects on species richness (Brown, 2014;
Jablonski et al., 2017). Educators who would like to have students
trace these scientific developments may want to include student interaction with papers and data that now challenge the evolutionary speed
model. For instance, new data on Squamata (lizards and snakes) do
not demonstrate a relationship between species diversity and latitude
or temperature, which challenges the evolutionary speed model for
this large and important group of animals (Rolland et al., 2016).
This novel curriculum can be used effectively in the postsecondary setting by those who teach aspiring science educators about ecology and evolutionary phenomena. Given that K–12 teachers are
required to implement inquiry standards, such as those indicated in
the Next Generation Science Standards, they will require experiences
that help them develop as educators who can support authentic science practices. Such practices include supporting students in constructing explanatory models to explain natural phenomena. As
other education-related organizations and policies dictate, postsecondary faculty teaching science courses that include aspiring educators will need curricula and related pedagogy to help their
postsecondary students explore phenomena in ways that parallel scientists’ practices. Ultimately, this teaching environment requires post-secondary educators who understand not only the processes of
inquiry (including modeling), but also how to facilitate such learning
experiences in their classrooms.
References
Adumat, S., Bouwma-Gearhart, J., Little, D. & Bouwma, A. (2011). Modeling-based curriculum and instruction in the undergraduate classroom:
engagement of students as communities of scientists. Proceedings of
the Annual Meeting of the American Educational Research Association,
New Orleans, LA. http://www.aera.net/Publications/Online-Paper-
Repository/AERA-Online-Paper-Repository/Owner/635669.
Bouwma-Gearhart, J. & Bouwma, A. (2015). Inquiry through modeling:
exploring the tensions between natural & sexual selection using
crickets. American Biology Teacher, 77, 128–133.
