Elements of life histories

The distribution of the 412 articles examined in volumes 5 to 27 of J-NABS that contained various elements of life-history studies varied from 3 to 13 per volume (Fig. 2). Numbers fluctuated greatly over time, and no clear temporal pattern of change in number of articles was detected. However, because the number of articles in each volume of J-NABS has tended to increase over time, the percentage of articles containing life-history elements generally decreased over time (Table 1). The earlier volumes (e.g., 5–15) contain a higher percentage of articles published in a volume (11.4–48.2%) than do later volumes (7.1–22.0% in volumes 16–27).

Of the 9 life-history elements examined, the topics studied most were growth (97 articles), followed by development (69) and mortality (67) (Table 1). In contrast, recruitment (12) and dormancy (20) were studied least. The only clear temporal difference was that voltinism, phenology, and dormancy were elements that were reported more often in earlier volumes, although more studies on recruitment have been published recently. Most studies (101) focused on a single life-history topic, with a range of 0 to 6 topics/study.

Life-history elements were studied for a variety of benthic organisms (Table 2). Most articles were about aquatic insects (158) and mollusks (60), especially bivalves (43), followed by Ephemeroptera (31), Diptera (27), and Trichoptera (24). Many studies dealt with multiple taxa, and 15 of the studies reported life-history information as a function of secondary-production studies (data not shown).

Detailed life-history studies

The 31 articles that reported detailed life-history studies varied from 0 to 4/volume (Fig. 2). A clear temporal trend was observed; more studies were published in the earlier volumes of J-NABS than in the later ones. This decrease is even more pronounced when the percentages of articles reporting detailed life histories in volumes 5 to 15 and 16 to 27 are compared: 6.2% in the earlier volumes (range 0–10.3% per volume) to <1% (range 0–4.0%) in the later ones.

The detailed life-history studies examined 84 species. This number exceeded the total number of studies conducted (31) because, as with life-history elements, several studies involved multiple species. Most of the species studied were in the order Ephemeroptera (23 studies), followed by Plecoptera and Trichoptera (13 each), and Odonata (11). Of the 35 different families examined, the Capniidae (Plecoptera) had the most species studied (10). Leptocerid caddisflies (7 species), libellulid dragonflies (6 species), and ephemerellid mayflies (5 species) also were studied commonly. Perhaps not surprisingly, no species was studied in ≥1 detailed life-history study published in J-NABS.

Natural history of benthic macroinvertebrates

The 1^st period was characterized by detailed descriptions of life cycles of benthic organisms, their adaptations to different aquatic habitats, and their life-history factors that might affect the abundance and distribution of their fish predators. Life cycle and life history refer to different phenomena (Butler 1984; Fig. 1). Life cycle refers to the sequence of morphological stages and physiological processes from one generation to the next. In contrast, life history denotes the qualitative and quantitative details of the variable events that are associated with that life cycle.

An important early development in life-history research was the establishment of permanent biological research stations along lakes and rivers. These centers (such as at Plön in Germany, Douglas Lake in Michigan, Sagehen Creek in California, and many other sites) provided logistical ease of observation and the opportunity to conduct extra research on topics that might have been tangential to the main programs of the research stations. In addition, these field stations were often in isolated locations, and life-history research often was viewed as a welcome diversion and became a hobby for both resident and visiting scientists. Likewise, the concurrent establishment of organizations emphasizing natural history and field research (e.g., the Illinois Natural History Survey) codified some of these activities as organizational goals.

Collections made at biological stations and field-research institutions have served as an important basis for examining faunal changes over time (Shaffer et al. 1998), and many examples are known for benthic macroinvertebrates (e.g., Resh and Unzicker 1975, Hall and Ide 1987, DeWalt et al. 2005). These studies have provided much useful information about life-history characteristics and the effects of anthropogenic activities. For example, such temporal surveys have demonstrated that long-lived taxa, such as predators, are most susceptible to extirpation, particularly in large rivers. Perhaps this sensitivity results from a life cycle that is too long to escape pollution episodes or anthropogenic activities that modify some requisite of their life history.

The importance of life-history research during this natural-history era was evidenced by the Ecological Society of America's establishment of the “Committee on Ecological Life Histories” (Fig. 1). Today, the term ecological life-history might seem redundant, but 40 y ago, this adjective was commonly used to emphasize the relationship of the life cycle to the environment.

Synthesis of information on life histories

The 2^nd period was characterized by the compilation of general information on the life histories of benthic organisms (most often insects) and syntheses of life-history information based on taxonomic groupings (e.g., aquatic insect orders) or specific habitat types. We see 4 sources of important information, and examples of each are presented in our timeline of key milestones in life-history research (Fig. 1). The 1^st of these sources is books published that included some information on the ecology of benthic macroinvertebrates. Early works, such as Isaac Walton's (1653)The Compleat Angler were written primarily for anglers. Over 300 editions of this book have appeared, and The Compleat Angler, along with the King James version of the Bible and the complete works of William Shakespeare are the 3 most published books in English literature!

Scholarly treatments started to appear at the end of the 19^th century (e.g., Miall 1895; Fig. 1) and continue into the 20^th century. They include Ward and Whipple (1918; Fig. 1), Hynes (1960, 1970; Fig. 1), McCafferty (1981; Fig. 1), Resh and Rosenberg (1984), Williams and Feltmate (1992), Ward (1992), Hutchinson (1993; Fig. 1), and Wichard et al. (1995, 2002; Fig. 1), and they continue to this day. For example, a variety of excellent textbooks, many intended for specialized university classes, and reference works are available (e.g., Hutchinson 1993, Thorp and Covich 2001, Merritt et al. 2008 [Fig. 1]), as are some for the general public (e.g., Voshell 2002). However, these academic books are a small portion of the market relative to the hundreds of books on this topic written for anglers engaged in the sport of fly fishing (e.g., Swisher and Richards 1991, Hafele and Roederer 1995).

The use of aquatic insects and other benthic macroinvertebrates in water pollution monitoring, which began in Germany over a century ago (Bonada et al. 2006), also resulted in the compilation of information on aquatic insect life histories and in particular their response to various types of pollution. Hynes' (1960) book on the Biology of Polluted Waters was instrumental in laying the foundations for this approach in North America. Plafkin et al. 's (1989; Fig. 1) manual on biological monitoring not only proposed guidelines for biologically based water-quality monitoring but also provided the first wide-scale use of a life-history characteristic, the use of functional feeding groups, in North American assessments. This manual was also the 2^nd-most cited article in the articles appearing in J-NABS between 1995 and 2000 (Resh and Kobzina 20031). Like biological monitoring, the discovery of the importance of the hyporheic zone in the life histories of insects (Coleman and Hynes 1970, Williams 1984; Fig. 1) sparked a great deal of study on this habitat and its faunal components.

The 2^nd source of life-history information is synthetic review articles. Numerous reviews on the life histories of aquatic insects (Macan 1962; Fig. 1) and most importantly specific insect orders or families, such as Trichoptera (Mackay and Wiggins 1979, Wiggins and Mackay 1979), Ephemeroptera (Brittain 1982), Plecoptera (Hynes 1976), Odonata (Corbet 1980), Chironomidae (Oliver 1971, Pinder 1986), and Tipulidae (Pritchard 1983), or groups, such as riffle beetles (Brown 1987), have been essential references that are widely used and cited by benthic biologists worldwide. These articles typically have appeared in the Annual Review of Entomology but one detailed review of species traits has appeared in J-NABS (Poff et al. 2006; Fig. 1). Furthermore, Hutchinson (1981) provided excellent “thoughts” on this topic that are still applicable, and Huryn et al. (2008) recently provided an excellent overview of life-history details of aquatic insects. Reviews also are available about the life histories of benthic organisms occurring in habitats other than streams and lakes. Adaptations to temporary ponds (Wiggins et al. 1980) and streams (Williams 2005), springs (Williams and Danks 1991), and the hyporheic zone (Boulton et al. 1998) illustrate the importance of habitat as a filter for life-history characteristics.

The 3^rd source is the special symposia or collections of articles that have been published on life-history topics. These collections include an older compilation (Rosenberg 1979) and more recent symposia published in J-NABS on benthic macroinvertebrates in temporary streams (Mackay 1996) and tropical streams (Wantzen et al. 2006).

The 4^th major source of information on life histories of benthic macroinvertebrates is the primary literature published in journals. Some of these articles have appeared in J-NABS (Fig. 2), but a very large number of studies (e.g., reviewed in the tables of Huryn et al. 2008) appear in other journals. Mendez and Resh (2007) provided data indicating that specialized publications might be more important outlets than general freshwater journals, such as J-NABS, in publishing this type of research. Mendez and Resh (2007) examined 100 of what they considered to be the most complete life-history studies published, in English, on Trichoptera to determine which aspects of the life history of the aquatic insects in this order have been studied most. These 100 studies were drawn from 32 different journals. Most articles (23) appeared in the 12 Proceedings of the Trichoptera Symposia, which are published every 3 y, followed by the Canadian Journal of Zoology (10), Archiv für Hydrobiologie (now called Fundamental and Applied Limnology) (8), Hydrobiologia (8), Aquatic Insects (6), American Midland Naturalist (4), Freshwater Biology (4), and Annals of the Entomological Society of America (4). In their list of 100 detailed life-history studies of Trichoptera, only 1 article had been published in J-NABS.

There are several explanations why other journals publish more life-history studies on Trichoptera (and probably other groups of benthic macroinvertebrates) than J-NABS. These include the number of articles that appear in a volume of a given journal and the length of time a journal has been publishing research. However, we think that a point not generally acknowledged is that editors of many scientific journals like J-NABS want to publish articles from which generalities can be developed or that present clearly unique examples of certain phenomena. In terms of life-history studies, meeting these criteria can be difficult. Some studies might appear to be incomplete because of logistical complications, such as a lack of multiple years or sites that limit comparative analysis, or insufficient physical-habitat (e.g., detailed and regular hydrologic measurements) information. In contrast, the editors of proceedings of special symposia (e.g., on Trichoptera, Ephemeroptera, Chironomidae, Oligochaeta, and other taxonomic groups) might be more interested in publishing the most information possible on individual taxa in those groups. Thus, these periodical compendia might be more important than broader-coverage journals as publication outlets for life-history research. Moreover, regional journals (e.g., Journal of the Kansas Entomological Society, Proceedings of the Entomological Society of Washington) and journals in which nonprofessional researchers publish (e.g., Entomologist Gazette, Entomologist's Monthly Magazine) also are important outlets for life-history research.

J-NABS might fill a special niche in terms of the large number of studies containing molluscan, especially freshwater mussel, life-history elements. Perhaps fewer outlets comparable to those listed above for aquatic insects exist for publication of research on freshwater mussels than for aquatic insects. Also, mollusks might appear more in these types of journals because they are often the topic of conservation issues.

Literature availability is a major problem in accessing life-history research. In a detailed literature review of reproductive traits of aquatic insects, Statzner et al. (1997) warned that many journals containing relevant and potentially valuable life-history information could not be found, despite extensive searching in libraries. This warning suggests that authors should chose to publish life-history information in journals that are well archived. Conversely, perhaps well-archived journals also have an obligation to publish research that has a “longer research life” rather than just this year's “hot topic” (Ioannidis 2005).

Functional-feeding groups

The 3^rd period was characterized by the use of the functional-feeding approach in North America. This approach was popularized by early review articles by Cummins (1973) and Cummins and Klug (1979; Fig. 1) and is based on morphological and behavioral mechanisms of food acquisition. Cummins et al. (2008) present the best overview of this approach as currently used, and Merritt and Cummins (2006) provide examples of how this life-history trait can be used as an ecosystem descriptor (e.g., Vannote et al. 1980) and in producing qualitative evaluations of stream-ecosystem health.

A perennial problem encountered by researchers using this trait is the way in which functional-feeding group categories are assigned. For example, Cummins (1988) stated that the original intent was to base functional distinctions on mouthpart morphology and means of food acquisition (as described in Cummins and Wilzbach 1985). However, researchers typically have assigned taxa to functional-feeding groups based on the ecological data tables in Merritt et al. (2008 and earlier editions) or derivative lists, which actually are based on digestive-tract analysis. Although widely used, we think it was unfortunate that the functional-feeding group was the first life-history trait to be applied quantitatively in North American studies because its use deviated from the authors' intentions from the start. Moreover, it is probably the most difficult of the life-history traits to quantify because the categories used are discrete (e.g., shredders, collectors, scrapers), whereas many benthic macroinvertebrates are omnivores or might belong to >1 functional-feeding group over the course their life cycle.

Species traits

The 4^th period is still underway and is characterized by the increased use of a species traits-based approach for water-quality assessments and for broad spatial and temporal studies of stream and river systems. Life-history information is essential to the description and quantification of species traits of benthic macroinvertebrates. The use of species traits has a long tradition in biology (Statzner et al. 2001), but the recent interest in these characteristics, which include potential size reached, voltinism, body form, and respiration technique, was initiated with the project of Statzner et al. (1994; Fig. 1) that synthesized 20 y of ecological research on the Upper Rhône River in France. There, >30 researchers designed and applied a strategy to test concurrently developed theories focused on the Habitat Templet Concept of Southwood (1977; Fig. 1). At the beginning of that study, Townsend and Hildrew (1994) predicted which species traits were likely to occur in a particular spatial-temporal templet, which assumed some positive relationship between temporal variability and frequency of disturbance, and between spatial variability and refugia from disturbance. Based on the results obtained from a variety of benthic macroinvertebrates (along with fish, macrophytes, and other organisms), Resh et al. (1994) emphasized the need for future studies to identify new traits for analysis, examine the tradeoffs between various combinations of traits, and focus on systematic groups that developed a consistent evolutionary solution to particular challenges of coping with environmental features of habitats. Following that call, Townsend et al. (1997) did a further test on species traits and habitat templet theory.

Until recently (e.g., Resh et al. 2005, Bêche et al. 2006, Poff et al. 2006, Bêche and Resh 2007), North American studies based on species traits focused predominantly on functional-feeding groups. Most of the research on the use of species traits has been published by Europeans and in non-North American journals, but the project on the Rhône River (Statzner et al. 1994) had a strong connection to NABS and J-NABS. The original idea for doing this type of analysis on a large, well-studied river came from a presentation by Colin Townsend at the Tuscaloosa NABS annual meeting (17–20 May 1998) that was later published in J-NABS (Townsend 1989). Furthermore, the first presentation of the Rhône results was at a special symposium at the Calgary NABS annual meeting (25–28 May 1993).

Theoretical and applied studies of species traits began to appear in the literature soon after the Rhône study was published. For example, Statzner et al. (1997) used information available worldwide to examine species traits related to reproductive biology of 131 species in 8 orders of aquatic insects. Numerous articles demonstrating how species traits can be used in biomonitoring of streams and rivers have been published (e.g., Charvet et al. 2000 [Fig. 1], Usseglio-Polatera et al. 2000, Gayraud et al. 2003, Bonada et al. 2006, Dolédec and Statzner 2010). More recently, Bêche et al. (2006) and Bêche and Resh (2007) used species traits to relate long-term community trends in benthic macroinvertebrates to annual flow variability, Resh et al. (2005) used species traits to explain why some taxa are temporally rare, and Bonada et al. (2007) compared traits of macroinvertebrate populations in Mediterranean and temperate regions to examine implications of climate change to benthic fauna.

Poff et al. (2006) recently made a major contribution to the study of species traits by providing a trait matrix in terms of life history, mobility, and morphological and ecological characteristics for genera of North American aquatic insects. They used this information to demonstrate how these traits can be used to predict responses of taxa to specific environmental gradients.

Information on species traits has come from several sources. The first source is the published literature (as in the study of Statzner et al. 1997). However, other studies have drawn on the individual expertise of specialists in a particular region (e.g., Statzner et al. 1994, Poff et al. 2006). In either case, this information is needed to conduct either applied or basic research using species traits.

Why are more life-history studies not done?

In the above discussion, we have pointed out why life-history studies are important and how information from them can be used. However, life-history studies clearly are not as widely done as in previous times. Why is this the case?

First, benthic biology, like other fields of ecological research, has entered a phase in which experimental research is viewed as worthwhile modern research, and unfortunately, descriptive studies often are viewed as the opposite (e.g., Greene 2005). However, life-history studies can be experimental, hypothesis-based, and predictive; furthermore, they can reset research cycles. Such studies can test whether aspects of a life history of related species are similar as would be predicted by phylogeny, whether local environmental features result in plasticity, or whether phylogenic factors override environmental response. Greene (2005) used the discovery of the marine benthic organisms of deep-sea thermal vents as an example of the types of life-history-related questions now being asked routinely and of new paradigms being developed. In 2009, the Ecological Society of America sponsored a symposium, with well known speakers, entitled “Natural History: The Basis for Ecological Understanding and a Global Sustainable Society” and a new electronic journal, Journal of Natural History Education has been started.

Second, life-history studies are time consuming. Multiple seasons and sometimes multiple years are needed to complete a detailed life history. Mendez and Resh (2007) examined 100 studies in terms of the length of field work done in completing life-history studies of Trichoptera and noted that study duration ranged from 1 to 11 y, with ∼80% of the studies lasting 1 to 2 y but many lasting 3 to 7 y.

Third, with few exceptions, funding for conducting life-history research is not available. Species of special concern (such as endangered or introduced and potentially pestiferous taxa) might qualify for direct life-history research funding, but the vast majority do not. Savvy benthic biologists interested in life-history research might refer to what they are doing as evolutionary biology or behavioral ecology, and some researchers have successfully packaged proposals in certain ways to emphasize broader concepts. In fact, life-history studies are an example of research that can be done without external funding and, for most of its history (and actually for most of scientific history), this has been the case. The early naturalists (and scientists in general up until the 1950s) supported their research themselves.

How we can increase attention to life-history studies?

In this special issue, Holzenthal et al. (2010) have decried the lack of taxonomic expertise among researchers for most of the groups of benthic macroinvertebrates. In taxonomy, new techniques (e.g., genetic barcoding), although controversial (Will and Resh 2008), might offer a shortcut to traditional approaches. However, we have difficulty imagining how new techniques could shorten the time needed to obtain the life-history information required for determining species traits. Ironically, we do see that, in terms of securing extramural funding, a proposal to use stable isotopes to determine feeding relationships might sound more sophisticated (and be more expensive and time consuming) than just examining gut contents!

If life-history information is needed, but the motivation to collect it is missing, how can we encourage more life-history research? To us, the answer is to involve the nonprofessional who is interested in aquatic ecology and entomology in this type of research. For example, in North America, tens of thousands of people are involved in volunteer monitoring groups that assess the environmental quality of streams (e.g., USEPA 1994). Japan has >800,000 people who participate in annual monitoring surveys using benthic macroinvertebrates (Morse et al. 2007). Moreover, throughout the world, hundreds of thousands of anglers are tying flies to imitate aquatic insects to “match the hatch” in their fly-casting efforts. We avoid using the possibly pejorative term, amateurs, to describe these people because their skills and abilities (and time commitments) often match those of professional aquatic ecologists and entomologists.

We have excellent examples of these self-trained aquatic entomologists who have made outstanding contributions to the study of life histories of aquatic insects. Clarence Day, a Vice President of Levi–Strauss (the famous jeans maker), published many articles on the biology and taxonomy of mayflies. Perhaps even more remarkable, Raymond Hays, a custodian at Montana State University, read literature about stonefly biology while being responsible for cleaning the zoology library at that university. His collections and studies made Montana's Hyalitte Creek (where he found 55 species in this insect order) one of the best-studied stonefly streams in North America. His contributions were noted by including him as a co-author of the faunal study of the stoneflies of Montana (Gaufin et al. 1972). Furthermore, scores of fisherman and hikers collected information on winter stoneflies as part of the “Winter Stonefly Club”, which was the basis for Ross and Ricker's (1971) seminal monograph on this group. Fly-fishing magazines and newsletters every month contain scores of columns describing intimate details of aquatic insect emergence, immature and adult behavior, and other life-history features that are written by self-trained entomologists. Certainly, the earliest people describing life histories of benthic macroinvertebrates (e.g., Isaac Walton) were entirely self trained!

The courses we teach to students also should emphasize what needs to be done in life-history research. Starting even earlier, suggestions for projects on aspects of life history make marvelous student science-fair projects for primary and secondary school students. In eastern Europe and Russia, teenage “eco-club” members often do life-history studies on stream invertebrates as part of their competitions; some of these studies are published in local natural-history journals.

When choosing which organism to use for a life-history study, we think potential researchers should keep certain characteristics in mind. First, the taxon selected should be readily distinguishable from other benthic macroinvertebrates in the field. For example, the presence of congeneric (or in some cases confamilial) taxa that cannot be easily separated from the study taxon could create difficulties. Early instars might not be distinguishable among these taxa, and the related taxa might have different phenologies that result in confounded patterns. Second, they should be easy to sample and be relatively abundant (or at least not rare). Third, and perhaps most important, the organism itself should be appealing to the researcher's interests.

Different groups also offer different study advantages. Holometabolous species are easier to use in phenology studies (and in descriptions of number of instars) than hemimetabolous species. Chironomids might be the group for which least is known in terms of life histories, but identification problems (particularly in the field) could make such studies difficult.

Although all of us conducting life-history research would like the species that we have selected to have some interesting, previously undescribed life-history characteristic, this feature unfortunately is rarely known in advance. However, even the most straightforward life-history patterns and characteristics are worth describing given the lack of this kind of information in the literature. In the end, the species chosen might have some unique features.

J-NABS can play an important role in advancing life-history and species-trait research by publishing review articles on the life-histories of different groups. Perhaps reviews that attempt to cover the biology of whole orders of aquatic insects have become too difficult a task, and competition for space in the few journals that publish reviews is too great to include them. Syntheses of life-history information on well-studied families, such as hydropsychid caddisflies or perlid stoneflies, or even genera, such as Baetis, might provide much needed information. Arguably, more synthesis of existing research is needed in all aspects of benthic science, and the popularity of the recent review of species traits by Poff et al. (2006) supports this view.

Last, both the value and the personal aspects of life-history studies should be stressed. A descriptive life history makes an excellent undergraduate or graduate degree thesis. Environmental influences and sources of ecological variation in populations can often best be described by taking a life-history approach. The point that we wish to make to both formally taught and self-trained students of benthic biology is that conducting and reporting life-history research is an important contribution and very enjoyable. In fact, a good life-history study provides a researcher a unique opportunity offered to few individual researchers: the chance to see life through another species' eyes.