This meeting, Special Session 2 at the 99th ESA meeting in Sacramento, California, was held on 11 August 2014. The discipline of ecology predates the Ecological Society of America, but ESA's 2015 centennial provides a fitting time to consider how ecology has evolved over the last 100 years, and how it is poised to advance and serve into the next century. How can we do this assessment? What are the metrics? How do we separate progress from mere change? Among the metrics for evaluating ecology's advancement we might calculate the gross accumulation of information, or list developments of new instrumentation and analytical techniques, or appraise improvements in predictive power. Or, we might weigh our ability to inform the public of environmental issues, and ecology's capacity to promote amelioration of the ever-expanding impacts of population growth, or to contribute to prevailing economic theories and technological developments. Another approach to assessing progress within ecology is to ask whether our conceptual tools are useful, appropriate, and sufficient for our needs. We were stimulated by ESA's Historical Records Committee to begin exploring such an assessment in preparation for the 2015 centennial, by developing a list of concepts and asking ESA members which of these were of value to their individual practices as ecologists, whether in education, research, monitoring, consulting, administration, or other pursuits. We use the term "concept" broadly but distinctly in this paper as a mental representation of an entity, process, or relationship. In our usage, concepts can take three forms. First, they can be presentations of entities that are relatively tangible such as "organism," or more abstract like "community." These we term ontologies. In different contexts, entities may be ontologies or claims of what is real. Second, in some contexts concepts may function as descriptors or features of entities (e.g., "biogeochemical cycle" is a feature of an "ecosystem"). In such cases we term the concept a metaphysical property. Finally we have concepts that are actual theories in the strictest sense: conceptual devices that systematically characterize the states and transitions of systems (e.g., second law of thermodynamics and natural selection). As we ecologists struggle to understand and explain nature and to predict its behavior, we attempt to incorporate interactions among biotic elements, and biotic with abiotic elements. This leads us to create concepts that are wholly intangible until we define them as particular cases. An "aquatic ecosystem" is intangible, whereas Walden Pond is a particular, tangible body of water we can treat as a system. We recognize, however, that Immanuel Kant was correct when he said we cannot really know the truth; our ideas of tangibility are largely operational, not declarations of objective truth. Our exploratory examination was performed in on 11 August 2014 as Special Session 2 of ESA's 99th Annual Meeting, held in Sacramento, California. After some introduction, we conducted an online survey of attendees with respect to their ranking of the usefulness of 105 concepts to their work. Results of the survey were calculated at a remote site within minutes and discussed during the rest of the session. In the introductory segment, we clarified the purpose of the session: To learn the degree to which 105 different ecological concepts were useful across the range of personal and professional variety of ecologists present at the session. We also carefully defined the term "concept" for our purposes, as described above. To obtain concept rankings in the context we desired, participants had to know some things about themselves. We explained that just as doctors have a variety of practices, so do ecologists. Thus participants were to view themselves individualistically, taking into account their particular knowledge, skills, tools, methods, and how they earned their living. We also explained that, like many of us, they might have a dualistic practice in which they taught, administered, consulted, or performed other tasks as an overlay to their special technical skills, knowledge base, and scientific interests. We emphasized that we wished them to rank the utility of the various concepts in terms of their scientific selves, not necessarily in terms of other work that might not be so directly scientific. We next explained the survey procedure. Participants could take the survey online with personal wifi enabled devices, or they could take it with a paper copy that we provided. The first part of the survey consisted of demographic questions: age; gender; highest degree; mode of employment (or retirement); primary domain of inquiry (population, community, etc.); primary method used to perform inquiry (field observations, experiments, etc.); and aspect of professional activity that provided the most personal satisfaction. These were used to sort rankings by different subgroups. The remainder of the survey consisted of scoring randomly presented sets of 65 concepts from a total pool of 105 from 1 (least useful) to 5 (most useful). The presentation of randomized subsets was intended to minimize effects of survey fatigue as well as order bias. The survey was closed after 20 minutes. While waiting for the results, we raised these questions for discussion and to set expectations for how the results were to be interpreted: Did it seem that the concepts differed from one another in some fundamental ways? How might concept rankings change with participant age? How might rankings vary with stage of career development? How might rankings differ with primary domain of inquiry? Did you, as a participant, learn something about yourself? Seventy-eight persons attended at least part of this session. We received 58 digital responses and 14 hard-copy responses. Only digital responses could be analyzed given session logistics. Some basic results were assembled for a poster and presented three days later (OPS 3-6 Ecological Concepts: Of what value, and for whom? Results of a survey), which can be viewed through this link: http://f1000.com/posters/browse/summary/1096732. We emphasize that these survey results come from a very small, self-selected sample of ecologists who were present at the 99th ESA meeting. No one should take these outcomes as actual representations of a statistically valid representation of the entire ESA membership. The primary value of the survey was as a learning experience for organizers and participants during the session. We exhibit the following data with some reluctance only as an example of how a larger survey outcome might be treated. Table 1 lists in descending order the 105 concept rankings calculated from the 58 digital survey responses (Table 1). Except for a relatively large drop between the first ("organism") and second ("population") concepts, and for the last four concepts in the sequence, the rate of decrease in rankings was essentially linear. The top-ranking concepts were ontologies and metaphysical properties; only three of the top 20 were theories by our definition. This suggests that concepts of basic entities, as opposed to theories (28% of total concepts), have the most utility for this population of participants. We sorted results by broad age classes: 20–30 year olds (36%); 31–50 year olds (34%); and >50 year olds (29%) (Table 2). All three age classes included three of the most common ontological concepts: "organism," "ecosystem," "population"; in the top 10 rankings along with " life history." Otherwise, there was limited overlap between the youngest class with the middle or oldest class, and more overlap between the middle and oldest class. Only the youngest class included "community" among its top 10 concepts. Only the oldest group placed high value on concepts related to evolution (selection, adaptation, microevolution), while the youngest group found abstract concepts pertaining to indeterminacy (e.g., gradient, species diversity, and complexity) particularly useful. We also sorted results by primary domains of inquiry (organisms, populations, communities, ecosystems, landscapes) which resulted in a predictable division of valuations for concepts (Table 3). Only the "organism" concept was common to all five domains, and only "population" was shared by three groups. Otherwise, choices are related to the nature of the domains, e.g. "energy flow" with ecosystems, and "edge effect" with landscapes. These domain results suggest a somewhat surprising lack of nested or hierarchical concepts. That is, although "organism" was judged to be a useful concept in all domains, "population" was not particularly useful for community ecologists and "community" was not especially useful for ecosystem ecologists. However, "ecosystem" was ranked 4th among landscape ecologists. The inverse also held true. In other words, "landscape" did not appear in the ecosystem ecologists" list; "ecosystem" did not appear in the community ecologists' list, and "community" did not appear in the population ecologists' list. Hence, it seems that each domain (N) did not generally identify either organizational level N − 1 or N + 1 as being particularly useful. The most useful concepts for a given domain were (with the exception of organisms) domain specific. From discussions during the latter part of the special session, and around the poster later in the week, we discovered that there is keen interest among some ecologists in identifying and evaluating concepts. Not surprisingly, this was especially apparent for those focused on the teaching of ecology. We were encouraged in these discussions to further this investigation by doing an on-line survey of the entire ESA membership. We also learned that some participants did not feel that concepts important to their specialty were listed. That discontent illuminated the fact that a defining context must be established for limiting concepts to those that make sense for this kind of survey. Every specialty in ecology—limnology, behavior, restoration, energetics—has its own particular concepts that are not, nor should they be, familiar to others. We were faced with determining what criteria can be used to generate an acceptable set for all ecologists. We realized that we were rather arbitrary in our choices of concepts for this preliminary survey experience, selecting many, like "organism," that can be found in the most general of ecology textbooks, but also including a few more arcane concepts, such as "holon," that only a few might have encountered. A more normative suite of concepts (i.e., concepts that ought to be understood) was needed to cross specialties in this kind of inquiry. The importance of a conceptual lexicon became more apparent during these discussions. Ecology's concepts—and there are many of them—represent the language and fabric of our discipline. But every individual thinks and works within a restricted portion of that fabric. Thus, the distribution of working concepts within that fabric represents the knowledge and practices of our ecological community. A normative set derived from some base level of experience is needed for survey like this, but such a limited set would be inadequate for a full appreciation of our full, disciplinary fabric. It also became apparent that ecology's conceptual array has a fascinating history. To know the influences that led to concepts through the history of our discipline is a way to understand the intellectual nature of our work. Knowing the birth, death, and inherited relationships among our concepts is one way to understand our field. Documenting and unraveling historical relationships between concepts deserves more attention. Our experience with this special session led us to reorganize the survey into a more tightly structured format that was launched to the entire ESA membership on 22 October this year. We restricted the concepts to a set we thought every ecologist might have experienced through a general ecology course. Concepts were selected from those found in at least two of the four most current general ecology texts. We regard these as "normative" concepts that are introduced at the most general, collegiate level, and should be a fair representation for an exploratory investigation like this. Results of this membership-wide survey will be reported at the 2015 Centennial meeting of ESA. We hope discussion of these results will lead to a further assessment of whether our conceptual fabric is as useful as it might be—and whether it is adequate for the challenges of ESA's next century.