Insights Into Ecology, Evolution and Global Change Responses From Very Long‐Term Studies

At a time where human activities are altering ecosystems and their associated biodiversity at unprecedented scales (Díaz et al. 2019; McFadden et al. 2023), there is a pressing need to understand how ecosystems function and how they have changed over time, to pinpoint the key processes structuring populations, communities and ecosystems, and to predict how ecosystems and the species inhabiting them will respond to ongoing change. Very long–term studies are crucial because many ecological and evolutionary processes unfold over long time scales, and because the links between cause and effect may take years to manifest (Table 1). Long-term studies enable not only documentation of changes that may be missed (or misperceived) in shorter term snapshots (Figure 1) but also a better understanding of the importance of year-to-year variability, including rare events, in shaping ecosystem dynamics and evolutionary responses to change (Franklin, Bledsoe, and Callahan 1990). Recent meta-analyses demonstrate the importance of long-term studies to correctly detect the direction of population trends (White 2019; Wright and Calderon 2025) and effects of experimental treatments (Cusser et al. 2021). Further, long-term studies allow for a closer integration between the fields of ecology and evolution (Jarne and Pinay 2023) as longer datasets increasingly capture evolution in action (e.g., Ålund et al. 2024; Johansson et al. 2024), thus enabling investigations of the roles of fundamental evolutionary processes such as phenotypic plasticity and maternal effects in adapting to change (Carroll et al. 2007; Räsänen and Kruuk 2007; Clutton-Brock and Sheldon 2010; Charmantier, Garant, and Kruuk 2014). Critically, such evolutionary responses are likely to differ substantially depending on organisms' pace of life and the environmental conditions encountered over individual lifetimes (Figure 2). Of course, even the longest observational and experimental studies are limited by the time scales of the human research endeavour, which are shorter than those of many ecological and evolutionary processes (Table 1). By collating a series of papers on very long-term studies in ecology and evolution, this special issue of Ecology Letters highlights the contributions of such studies to advancing our understanding of ecological processes and evolutionary mechanisms. Here, we summarise key findings from the papers in this special issue, grouping them into six areas of research: (1) ecological responses to temporal climate variation and climate change; (2) tipping points and regime shifts; (3) synchrony, stability and stationarity; (4) demographic and environmental determinants of population growth rates; (5) evolutionary patterns and potential and (6) causes and life-long consequences of behaviour. We close with a discussion of their potential to provide structure for inclusive education and professional development, a topic addressed at a greater length by Czapanskiy et al. (2024). A key strength of very long-term studies is their ability to document how species, communities and ecosystems respond to temporal climate variation, including long-term directional climate change. Interannual climate variation is affected by multiple global climate oscillations acting on different timescales, including the El Niño Southern Oscillation (2–7 years), the Pacific Decadal Oscillation (20–30 years) and the Atlantic Multidecadal Oscillation (60–90 years) (McCabe and Palecki 2006). These oscillations, together with the directional forcing due to increasing atmospheric carbon dioxide, mean that climate variation is temporally autocorrelated at a range of timescales and that studies of just a few years invariably fail to capture the breadth of climate variation (Figure 2). Because ecology is highly sensitive to climate, ecological conclusions based on short-term studies are inherently fragile. Climate-related changes in phenology—the seasonal timing of life cycles—have been particularly well studied (Parmesan 2006; Chmura et al. 2018; Inouye 2022). Insofar as such phenological shifts are asynchronous among interacting species, they may alter competitive and trophic dynamics, affecting population performance (Iler et al. 2021) and overall ecosystem function (Beard et al. 2019). In this special issue, Fournier et al. (2024) analyse the covariance of > 2000 long-term time series of monthly data on the seasonal timing of peak abundance of fish, zooplankton and phytoplankton, together with changes in temperature and salinity, across three major estuarine ecosystems in North America over a period of ca. 30 years. They found that over a quarter of the studied taxa showed significant shifts in phenology, the vast majority advancing their phenology over time in response to changing temperature and salinity. However, 29%–68% of taxa within each trophic level did not appear to be tracking environmental changes in temperature or salinity through measurable phenological responses. In addition, phenological trends sometimes diverged substantially within and among trophic groups (e.g., fish and zooplankton communities) within regions, indicating high potential for trophic mismatches that could disrupt food-web dynamics. Besides trophic mismatches, climate-induced phenological shifts may cause developmental mismatches in some taxa, possibly leading to the so-called ‘ecological traps’ (Schlaepfer, Runge, and Sherman 2002). For ectothermic insects that rely on temperature to complete critical stages of their life cycles, extended thermal windows for larval development may enable an increase in the number of generations per season (i.e., voltinism, Altermatt 2010). However, because cues from a warming environment may conflict with actual seasonal change as defined by photoperiod, insects run the risk of losing a generation if the season ends before development of the final generation is completed, the larvae then not having undergone the necessary physiological preparations for diapause or winter dormancy (the ‘lost generation’ hypothesis; Van Dyck et al. 2015). Here, Wepprich, Henry, and Haddad (2025) test for the potential of ‘lost generations’ across a long-term study spanning 27 years and 30 multivoltine butterfly species. Voltinism shifts were overall beneficial to the majority of butterfly species: shifts towards larger last generations generally positively affected species' overwinter population growth rates and long-term population trends. ‘Lost generations’ were rare, occurring only under limited environmental conditions in a few species. Nonetheless, abundances declined over time in the majority of species, emphasising the need for continuous long-term monitoring and further investigations into the underlying causes of decline. Very long-term studies are also critical to capturing the effects of extreme events, and quantifying the magnitude and duration of their effects. Using long-term time series spanning over 30 years of fisheries investigations and a US. long-term ecological research (LTER) site, Chen et al. (2024) study the consequences of multiple marine heat waves of varying intensity and duration for phytoplankton, zooplankton and fish in the southern California current ecosystem. Half of the 30 groups analysed exhibited statistically significant responses to heatwaves, with 14 of 15 showing negative responses, and variation among groups in whether they responded more strongly to intensity or duration. Further research is needed to elucidate the consequences of these variable responses for trophic interactions. Not only may species differ in their climate responses depending on their own traits, but these responses may themselves depend on the traits and responses of interacting species. Using 30 years of data on growth of tropical trees of 89 species in 15 Amazonian plots, Nemetschek et al. (2025) showed that neighbourhood functional composition and diversity affected tree growth and its response to climate anomalies. Greater functional diversity (trait dissimilarity) among neighbours promoted tree growth. Further, neighbourhood interactions and functional diversity mediated community-level effects of above average maximum temperature, vapour pressure deficit and climatic water deficit. At a community level, water-demanding species increased climatic stress for water-saving species by decreasing water availability, whereas water-saving species reduced climatic stress for water-demanding species. Effects of climate variation may be mediated through multiple climate variables and pathways, as found by Vleminckx et al. (2025) in their 22-year study of seed production in an ever-wet Amazonian forest. Despite moderately positive effects of higher daytime temperatures, community-level seed production decreased due to direct and indirect (via flower production) effects of increasing nighttime temperature and decreasing water vapour pressure deficit. Rainfall also affected seed production, with contrasting effects depending on seasonal timing: rainfall early in the fruiting year reduced same-year seed production, whereas rainfall at the end of the fruiting year increased the next year's seed production. These effects are important not only for plant regeneration but also for the many species of pollinators, frugivores and granivores that rely on flowers, fruits and seeds for food. Improved understanding of how climate variation influences demographic performance and abundance at population and community levels is important not only for fundamental ecological understanding but also because of its relevance for conservation and management. For example, very long-term studies documenting such climate responses can be used to parameterize models to project responses to future climate change scenarios. This is what Jeglinski et al. (2024) did in a study drawing on 116 years of abundance data (1900–2016) for the Northeast Atlantic metapopulation of the northern gannet and fecundity data for a subset of those years. Given the ubiquity and magnitude of anthropogenic pressures, it is critical to understand the resilience or vulnerability of natural ecosystems to disturbance and change (Holling 1973). What are the tipping points (if any) beyond which regime shifts occur and systems transition to alternative equilibria with different functional and structural organisations? Studies that encompass multiple disturbances and their aftermaths are uniquely well positioned to shed light on these questions. Graham et al. (2024) investigated resilience of coral reefs across the inner Seychelles islands following two marine heatwaves and associated mass coral bleaching events occurring some 20 years apart, through analyses of data on hard corals, soft corals, macroalgae and fish. The first heat wave and mass mortality event were followed by recovery in some coral reefs and a regime shift to macroalgal domination in others. The reefs that recovered from the first mass mortality event were more resistant to community change and recovered more rapidly from the second mass mortality event than those having undergone regime shifts, suggesting an increase in ecosystem resiliency following repeated stressors through time. Graham et al. (2024) also reported a regime-shift reversal, one of the reefs transitioning back to a coral-dominated regime following the second heatwave, further evidence that some coral ecosystems may be more resilient than previously thought. Riginos et al. (2024) address resilience in a savanna ecosystem in Kenya, drawing on 29 years of results from a long-term large herbivore exclosure experiment to synthesise lessons learned on short- and long-term ecosystem responses to multiple stressors, including drought, herbivory pressure and wildfire. The experimental treatments restricted access of one, two or three groups of large herbivores: cattle, wild mesoherbivores (25–800 kg) and wild megaherbivores (> 1000 kg). The different exclosure treatments resulted in different significant shifts in herbaceous communities and in soil chemistry, which were only detectable after 5–10 years and after 20 years, respectively. The long-term nature of the study was critical to capture oscillating patterns in ecosystem dynamics contingent on rainfall, in particular related to the competition–facilitation balances between cattle and wildlife, and between different plant species. Temporal climate variation interacted strongly with experimental treatment: the first rainy year after each drought proved an important inflection point for accelerating changes in plant community composition contingent the herbivore The of data analyses of longer term ecosystem stability and these studies how long-term monitoring of natural ecosystems and long-term experimental treatments each in tipping points in ecosystem populations, communities and ecosystems over time due not only to temporal variation in climate and but also in many to dynamics (e.g., The nature and of temporal variation, its causes and its consequences are of fundamental to and also important for understanding the resilience and vulnerability of species, communities and ecosystem and thus for conservation and management. among temporal of interacting species, whether or to what temporal variation is in species within or over within species, and how variation in with diversity and environmental to temporal variation (or in across species or and thus to and and multiple species in synchrony, then community and ecosystem temporal variation will be higher than if species The more species differ in their responses to climate and that over time, the more we communities are to more variation in responses, to a that and stability in to positive effects and many studies of on et al. (2024) the of seed production among plant species within Temporal from asynchronous to highly was greater for species traits, but not those more was also higher in by higher water because drought conditions more or in or species, community seed production in years. This study on many studies documenting defined by high and temporal variation in seed production. into the of seed production in multiple species are rare and shed light on as well as the larger needed to understand consequences for plant regeneration and to species. studies in this special issue investigated in abundance stability of and three the of the of diversity to stability from studies in which diversity is not but is an that on that also and (2025) investigated and stability in fish communities on the drawing on data from a time period for in a by the of the The the of abundance into two and average population and They found that substantially to variation, with with of diversity for community-level and were in communities with higher but this was by environmental In reefs closer to the and thus more to anthropogenic and decreased increased and increased community-level whereas more reefs from the higher and greater This study to the of evidence that anthropogenic many species increasing and community-level et al. (2025) also addressed among species synchrony, population stability and community stability very long-term observational data for multiple They analysed years of data from many in for six phytoplankton, and large and substantially among For example, more variation in community stability than did population stability in and phytoplankton, whereas population stability more in and large studies for environmental influences on stability and et al. (2025) of a long-term experimental study in a to how plant and stability are by global change Effects between an period of years and a period spanning years after experimental The final structural models for the period significant negative effects of level on and and of on but links from or to or results for the period the results the importance of long-term studies and also how the in and stability can from effects of an environmental and need not for effects of diversity on the above studies analyse data on species abundances to within a particular et al. (2024) such data for two to trophic dynamics. They on and abundance data for also used by et al. with functional to by functional and by site, and test the of abundance to Of the for influences of on in a only were significant at the level, of which two were results that temporal variation in abundance is not related to abundance as be from effects In to the above studies quantifying (or the among species within et al. (2024) on across within species. They analysed species for species, for in temporal among long-term each over and together spanning some 1000 of across Using for in associated with conditions and they found significant variation in temporal patterns for 14 of the species, indicating a of or with the of synchrony, the effects of a (e.g., on an ecological (e.g., population across time. in was not related to the from a species' was it related to variables and These results that responses of species at global scales may differ substantially from those at scales, with important for fundamental of ecology is understanding the shaping population growth the demographic to and decline. of population growth rates that a (or is through time and thus that population growth can be through its long-term of growth However, ecological are variable by and events (e.g., may to changes in a In such the growth may differ substantially from the short-term population growth The development of life response this by quantifying the of population rates to population growth for temporal variation in rates and demographic structure et al. In this issue, two papers to environmental and demographic variables to population growth et al. (2024) the of demographic environmental on population growth rates of population increase and and the that traits with the on population growth the of variation over time and et al. In a population that through an period of followed by a and a they showed that the demographic population growth or were the and to environmental of the in the population growth to the demographic the demographic cause of in abundance of was which substantially among years. and species more is to and diversity and population long-term et al. et al. (2024) studied the consequences of anthropogenic and increasing on the rates of over a They found that population stability was increased and to in rates together with results provide rare into of a Long-term studies provide to study dynamics Garant, and and evolutionary including that due to anthropogenic For example, warming are to for and longer in to increase the for heat and et al. 2021). evidence that changes in are occurring in some wild populations, but studies are needed to the of this across taxa et al. et al. (2024) reported on a study of change in species. were with negative trends for mass in of species and for length in of species. In trends in length were highly variable among species, with a towards an increase in changes in were with to heat in warming phenotypic shifts could have been due to pressures, such as increased of phenotypic on changes in evolutionary responses et al. For example, to and with have a also occur through direct (e.g., or (e.g., of phenotypic how the of is important because associated with high increase in in because of the of between and to the of and patterns of are rare because long-term and data are to statistically of variation Garant, and Kruuk 2014). Ålund et al. (2024) used a very long-term study of to evidence patterns of from and analyses and they found but higher of this larvae indicating its with between and strongly in with for Besides phenotypic ability of a to multiple a key of 2021). traits, in responses to environmental their plasticity varying within and among et al. and The of plasticity across together with positive a of plasticity in one may plasticity in and Johansson et al. (2024) these a data of repeated on > and associated climatic and They found positive in for two and and for two and but a negative between a and for plasticity and between individual plasticity and with environmental a with the of in natural long-term studies enable of the causes and of particular The strength of long-term studies is that they have the to analyse of over the lifetimes of as well as to the to which of over time, for example, in response to changing environmental This is particularly important for understanding the of that occur over the lifetimes of such as or been in the vast majority (> of species and at highly variable rates among species and on its depend on the used to study the consequences of such a and Sheldon 2015). the season after for may be as per may be on a monitoring of Seychelles et al. (2024) analysed of which in and in with some to three in their for the and rates in and possibly to of and did not higher short- or long-term that their early in life in of life than that showing that the consequences of may be a of from to as for related Using a et al. (2024) analysed the life of and over a long-term study of Despite generally than and after to and for and long-term Critically, and rates were affected by conditions through direct effects on the processes and indirect effects mediated through or future climate trends the the further showed that is to possibly in with likely consequences for population important in many species of and is which influences individual and population et al. (2024) how change with abundance among years through analyses of years of for species in a of forest. In species, declined in years of higher and did in more and with of the The thus the that are to large even in years of greater abundance and These findings are for conservation and as with the of the is to to of and reduced risk of Long-term research can provide for inclusive education and professional development, as by Czapanskiy et al. (2024). years of on a long-term study of northern they key points that long-term studies of inclusive (1) data enable and with a level of beyond that from shorter term research (2) and research provide inclusive points into the of of the above allow to research and to a long-term research larger than the individual In addition, long-term studies professional development through (3) the of between at multiple the research and of and (4) that and and Czapanskiy et al. (2024) that the of many long-term research on is a critical acting and in long-term findings from responses of 27 for this Ecology Letters special issue found that whereas long-term studies at in on for data than some of to is in ecological and evolutionary this is in that it to for of time, which of many groups and 2015). Czapanskiy et al. (2024) that one to the of the necessary to long-term research by and is long-term with and an many (e.g., are By in a of very long-term studies may well a in the are more likely to and in in the future et al. and thus be in a to themselves further to the of long-term data the in this special issue of Ecology Letters the breadth and of fundamental and by very long-term The datasets and together with the in these special them even more enabling to more on these contributions with further analyses of these data or of the to of these contributions were highly by our data for their in and data in a and (e.g., et al. At the time, of of data to data can be particularly for very long-term studies et al. 2022). This is by that in a of and to papers et al. Very long-term studies are crucial for quantifying and effects of climate and global understanding ecological and evolutionary processes that unfold over data to and and and and et al. Further, such long-term generally for a range of investigations and communities of advancing understanding et al. and Wright At a time the of research short-term of years at it is critical to the contributions of very long-term and to the importance of in such and the We for with one in the associated special The for this is at and data for the are on