Long-term studies: why or why not?
Despite these examples, the deterministic ecological benefits of a
long-term study are likely to outweigh the influence of the stochastic
forces associated with when the study is initiated. This leads us to the
last issue we discuss, which is what we have learned conducting
long-term studies during our careers. Of course, all long-term studies
are different; ours involved intense field work, especially during
certain parts of the year, at least some of which could not easily be
passed on to graduate students or assistants.
Providing opportunities for new discoveries and to change one’s
mind. This includes discovery of new phenomena and ideas, fixing
errors, and gaining a more nuanced understanding of a system. In our
case, examples of discovery included joint nesting (females laying eggs
in the same nest) and egg destruction, whereby joint-nesting females
destroy each other’s eggs prior to laying their own in the same nest
cavity (Mumme et al. 1983). The latter was first observed in 1981, seven
years after the senior author started working on the project and 11
years after the project was initiated. Taking a long-term perspective
also provided us with the opportunity to add to the project in ways that
proved more valuable than anticipated. This included adding an annual
survey of acorn production, a project that eventually morphed into its
own (very) long-term project (Koenig et al. 1994, Pearse et al. 2014).
As for correcting errors (or, more generously, gaining a more nuanced
view of the system), for years we claimed that the primary constraint
forcing young birds to delay dispersal was the necessity of having a
granary in which groups could store acorns. Not until 2006 did we
conduct an experiment testing this assertion. Much to our surprise, the
results indicated that cavities for roosting and nesting are as
important a constraint to dispersal as granaries. Devoting decades of
study to a system does not make biases truer than they were when the
study was new.
Taking advantage of the march of science. One particularly
valuable benefit of a long-term study is that technological and
conceptual advances can be incorporated into the project. For us, an
example was determining parentage, a near impossibility when the project
started, yet crucial to understanding the social system (Dickinson et
al. 1995, Haydock et al. 2001). Another example was remote tracking
technology, which has advanced from old-school radio-tracking to
solar-powered nanotags detectable by computer-controlled base stations
(Barve et al. 2020). Other advances have been conceptual and involve
investigating new and trending analyses, such as social network analysis
(Shizuka et al. 2022). Such advances provide opportunities to expand a
study in new and exciting ways.
Long-term projects: beyond Polya’s urn. Results of long-term
studies will reflect a combination of intrinsic stochastic and
deterministic forces. Factors extraneous to the study are also changing,
however. Such changes can be catastrophic, such as the loss of a study
site. (Take heed: if a long-term study might be in your future, choose a
site that is likely to be available decades in the future.) Others
involve changes to the researchers, which may result in getting higher
quality data if methods are improving or lower quality data if one
cannot see or hear as well as one once could.
With luck, changes can be capitalized on, climate change being an
obvious example. Others may be more subtle and difficult to discern. In
our case, for example, the changing structure of the habitat due to
recovery since the ranching era has led to considerable vegetation and
population changes that we are still trying to understand (McMahon et
al. 2015, Hagemeyer et al. 2023).
Starting a long-term project. We suspect that few workers start
out with the thought of doing a study that will last for decades. Many
such studies exist, however, as evidenced by this special issue. All
that is necessary is to continue a project year after year; long-term
status will come sooner than you think. Initially a system may seem
simple, but it can take a long time to figure out what one does not
know. With each passing year, we generate more questions than answers.
The payoff of a long-term project is that it can provide a solid
research program for an entire career (and beyond). Ultimately, with
years of data and voluminous background information, having enough data
to address questions of current interest and writing a fundable proposal
can be considerably easier than starting an entirely new system. Decades
of background data can be a considerable advantage when competing for
funding.
The downside is maintaining funding and making sure that time-sensitive
data are collected year after year. In the U.S., the former has become
easier with the advent of special programs such as LTREB (Long Term
Research in Environmental Biology), but maintaining a long-term project
will always require thought, flexibility, a long-term commitment, and
potentially consideration of succession. Depending on the project,
missing even a single year can be disastrous. Given life’s vagaries,
this can be problematical.
As daunting as such problems may seem, the perspective that a long-term
study provides can clarify the multiple factors at play, whereas
short-term data are far more likely to mislead one into thinking there
are simple answers to complicated problems. The years during which a
study is conducted may have a strong, stochastic influence on results,
potentially rivaling the importance of a researcher’s interpretation of
those results. But having long-term data at least allows one to ask how
important such stochasticity is compared to the deterministic ecological
factors that we are all trying to understand.