Combinations Of Life History Traits Research Articles

The response of marine fish population productivity to juvenile habitat modifications depends upon life histories

AbstractCoastal and estuarine habitats are essential for both growth and survival at juvenile stages for a large proportion of marine fish but are exposed to a variety of threats. However, the quantitative impacts of anthropic‐mediated nursery degradation on exploited population dynamics and productivity are rarely addressed. We developed a comprehensive steepness‐based parameterization of the stock–recruitment relationship that directly depends upon juvenile habitat quality and surface area and used a generic age‐ and stage‐structured model to simulate exploited population dynamics under nursery degradation/restoration scenarios. Population responses to juvenile habitat modification were estimated for three species with contrasting life histories. Modifying the surface area of nursery habitat has a predictable direct scaling effect on population size and affects biomass and fishing yield, with identical responses observed for various life histories. Modification of habitat quality affects both the population size and the shape of the productivity curve, leading to more complex responses of biomass and fishing yields that depend upon combinations of life history traits. Populations with low steepness and hence lower resiliency to fishing are the most sensitive to the degradation of habitat quality. Our study emphasizes the critical impact of juvenile habitat modification on population dynamics and productivity and the need to integrate habitat consideration into the management of exploited marine species. Our modelling framework is generalizable and can be extended to handle many diverse life histories and case studies to quantify the consequences of coastal habitat degradation/restoration for the dynamics of exploited marine fish populations.

Functional and Taxonomic Overlap in Shore Fish Assemblages in a Tropical Seascape

The relationships between shore fish assemblages from habitats neighboring coral reefs have received little attention in the Indo-Pacific. The present study is based on the extensive sampling (539,000 fish; 898 taxa) of three fish assemblages: reefs, mangroves, and soft-bottoms in a large bay of New Caledonia. Species area curves indicate that sampling was nearly exhaustive in all three habitats (262 species in mangroves, 342 on soft-bottoms, 594 on reefs). Combinations of life-history traits were used as proxies of ecological functions. The species and functional overlaps were highest between soft-bottoms and mangroves and lowest between mangroves and reefs. These overlaps were lower than most recent studies in the Indo-Pacific, a result probably linked to the extent of the sampling in the present study. The life-history traits of species found exclusively in one habitat as opposed to several habitats were not a random selection within the species pool. Overlapping species were mostly large species that fed on nekton, large invertebrates, or plankton; exclusive species were mostly sedentary, solitary, and of small size, except for plankton-feeding species, which mostly had large home ranges and formed large schools. Herbivores were seldom found in several habitats. Functional redundancy was correlated to species richness, and was highest in reef fish assemblages. Functions common to several habitats had very seldom the same relative redundancy, implying that these functions had not the same importance for each assemblage. Functions exclusive to one habitat generally had low redundancy. These functional attributes and species overlap suggest that these three assemblages have a low level of interaction, despite the fact that they share extensive boundaries. These findings may have important applications in the management of shore fish assemblages.

On tree longevity.

Large, majestic trees are iconic symbols of great age among living organisms. Published evidence suggests that trees do not die because of genetically programmed senescence in their meristems, but rather are killed by an external agent or a disturbance event. Long tree lifespans are therefore allowed by specific combinations of life history traits within realized niches that support resistance to, or avoidance of, extrinsic mortality. Another requirement for trees to achieve their maximum longevity is either sustained growth over extended periods of time or at least the capacity to increase their growth rates when conditions allow it. The growth plasticity and modularity of trees can then be viewed as an evolutionary advantage that allows them to survive and reproduce for centuries and millennia. As more and more scientific information is systematically collected on tree ages under various ecological settings, it is becoming clear that tree longevity is a key trait for global syntheses of life history strategies, especially in connection with disturbance regimes and their possible future modifications. In addition, we challenge the long-held notion that shade-tolerant, late-successional species have longer lifespans than early-successional species by pointing out that tree species with extreme longevity do not fit this paradigm. Identifying extremely old trees is therefore the groundwork not only for protecting and/or restoring entire landscapes, but also to revisit and update classic ecological theories that shape our understanding of environmental change.

Unusually Paced Life History Strategies of Marine Megafauna Drive Atypical Sensitivities to Environmental Variability

Understanding why different life history strategies respond differently to changes in environmental variability is necessary to be able to predict eco-evolutionary population responses to change. Marine megafauna display unusual combinations of life history traits. For example, rays, sharks and turtles are all long-lived, characteristic of slow life histories. However, turtles also have very high reproduction rates and juvenile mortality, characteristic of fast life histories. Sharks and rays, in contrast, produce a few live-born young, which have low mortality rates, characteristic of slow life histories. This raises the question if marine megafaunal responses to environmental variability follow conventional life history patterns, including the pattern that fast life histories are more sensitive to environmental autocorrelation than slow life histories. To answer this question, we used a functional trait approach to quantify for different species of mobulid rays, cheloniid sea turtles and carcharhinid sharks – all inhabitants or visitors of (human-dominated) coastalscapes – how their life history, average size and log stochastic population growth rate, log(λs), respond to changes in environmental autocorrelation and in the frequency of favorable environmental conditions. The faster life histories were more sensitive to temporal frequency of favourable environmental conditions, but both faster and slower life histories were equally sensitive, although of opposite sign, to environmental autocorrelation. These patterns are atypical, likely following from the unusual life history traits that the megafauna display, as responses were linked to variation in mortality, growth and reproduction rates. Our findings signify the importance of understanding how life history traits and population responses to environmental change are linked. Such understanding is a basis for accurate predictions of marine megafauna population responses to environmental perturbations like (over)fishing, and to shifts in the autocorrelation of environmental variables, ultimately contributing toward bending the curve on marine biodiversity loss.

Resolving associative patterns in life history parameters among marine fish stocks in the Northeast Pacific Ocean

Knowledge of life history characteristics in marine fishes, including natural mortality, somatic growth, maturity schedule, productivity and others, is essential for successful management and long-term sustainability of marine resources. Patterns exist among these traits within and among taxa to maximize individual fitness and offspring survival, and trade-offs are typical. In this study, we examined life history data from 42 fishery stocks in the Northeast Pacific Ocean using principal component analysis (PCA) and clustering techniques. We identified discrete clustering patterns of stocks corresponding to ecological, taxonomic, and management criteria. Our results revealed additional resolution for complex structure among stocks based on combinations of life history traits, well beyond what was described before, for the diverse group of Sebastes rockfish, which have not been examined in this context previously. One example is clear differentiation between Sebastes demersal species, and those caught with midwater gear, particularly with addition of stock-specific fecundity data; another is bocaccio rockfish, whose life history patterns our results shed new light on. Our results also provide an empirical basis for grouping stocks in meta-analytic studies, which are often used to inform unknown or difficult to estimate parameters in stock assessment. Our results supported important core aspects of previous studies, and rectified others, among a wide range of stocks including highly migratory, coastal pelagic and groundfish stocks. They also reinforce fishery management strategies grounded in life history, among stocks in the Northeast Pacific Ocean and around the world.

Overgrazed shrublands support high taxonomic, functional and temporal diversity of Mediterranean ground spider assemblages

The phryganic and maquis shrublands form the most typical vegetal formations in the Eastern Mediterranean that since thousands of years have been subject to various types of anthropogenic disturbance, including grazing. We studied the impact of sheep and goat grazing on 50 assemblages of ground spiders (Araneae: Gnaphosidae) in phryganic, maquis and forest habitats from zero to 2000 m elevation on Crete, Greece using pitfall traps for one year at each sampling site. In total, 58 gnaphosid species and 16,592 individuals were collected. Cretan endemic Gnaphosidae were negatively affected by intensive grazing and, contrary to findings on other taxa studied on the island, they were sparse and rare throughout the study area. The species composition of gnaphosid assemblages was primarily determined by elevation. Trachyzelotes lyonneti, Urozelotes rusticus, Zelotes scrutatus, Anagraphis pallens and Berinda amabilis proved to be significant indicators of overgrazing. The vast majority of spiders belonging to synanthropic and nationally red-listed species were found in overgrazed sites. Despite theoretical expectations, while the average activity density decreased, the number of species, evenness, rarity, taxonomic, temporal and functional diversity (FRic) indices increased with increasing grazing intensity. This was mainly due to the nature of disturbance itself, which probably allows equibalanced low abundances of indigenous or synanthropic species, rather than overdominance of few, thus partly refuting the opportunistic species hypothesis (OSH). Ground spider assemblages in overgrazed sites comprised sparse populations of mostly rare, opportunistic species with different combinations of life-history traits that partly replace other species more commonly found in the less degraded sites. Species of these assemblages shorten their phenologies to minimize temporal co-occurrence with each other due to resource limitation. These distinct community patterns highlight ground spiders as good indicators of grazing pressure on Crete, on species and assemblage level. To conserve the indigenous and potentially endangered invertebrate fauna, the spatiotemporal discontinuity of grazing including rested patches is important in order to maintain spatial variability and possibly lead to habitat restoration.

Life-history traits predict perennial species response to fire in a desert ecosystem.

The Mojave Desert of North America has become fire-prone in recent decades due to invasive annual grasses that fuel wildfires following years of high rainfall. Perennial species are poorly adapted to fire in this system, and post-fire shifts in species composition have been substantial but variable across community types. To generalize across a range of conditions, we investigated whether simple life-history traits could predict how species responded to fire. Further, we classified species into plant functional types (PFTs) based on combinations of life-history traits and evaluated whether these groups exhibited a consistent fire-response. Six life-history traits varied significantly between burned and unburned areas in short (up to 4 years) or long-term (up to 52 years) post-fire datasets, including growth form, lifespan, seed size, seed dispersal, height, and leaf longevity. Forbs and grasses consistently increased in abundance after fire, while cacti were reduced and woody species exhibited a variable response. Woody species were classified into three PFTs based on combinations of life-history traits. Species in Group 1 increased in abundance after fire and were characterized by short lifespans, small, wind-dispersed seeds, low height, and deciduous leaves. Species in Group 2 were reduced by fire and distinguished from Group 1 by longer lifespans and evergreen leaves. Group 3 species, which also decreased after fire, were characterized by long lifespans, large non-wind dispersed seeds, and taller heights. Our results show that PFTs based on life-history traits can reliably predict the responses of most species to fire in the Mojave Desert. Dominant, long-lived species of this region possess a combination of traits limiting their ability to recover, presenting a clear example of how a novel disturbance regime may shift selective environmental pressures to favor alternative life-history strategies.

Causes and implications of the correlation between forest productivity and tree mortality rates

At global and regional scales, tree mortality rates are positively correlated with forest net primary productivity (NPP). Yet causes of the correlation are unknown, in spite of potentially profound implications for our understanding of environmental controls of forest structure and dynamics and, more generally, our understanding of broad-scale environmental controls of population dynamics and ecosystem processes. Here we seek to shed light on the causes of geographic patterns in tree mortality rates, and we consider some implications of the positive correlation between mortality rates and NPP. To reach these ends, we present seven hypotheses potentially explaining the correlation, develop an approach to help distinguish among the hypotheses, and apply the approach in a case study comparing a tropical and temperate forest. Based on our case study and literature synthesis, we conclude that no single mechanism controls geographic patterns of tree mortality rates. At least four different mechanisms may be at play, with the dominant mechanisms depending on whether the underlying productivity gradients are caused by climate or soil fertility. Two of the mechanisms are consequences of environmental selection for certain combinations of life-history traits, reflecting trade-offs between growth and defense (along edaphic productivity gradients) and between reproduction and persistence (as manifested in the adult tree stature continuum along climatic and edaphic gradients). The remaining two mechanisms are consequences of environmental influences on the nature and strength of ecological interactions: competition (along edaphic gradients) and pressure from plant enemies (along climatic gradients). For only one of these four mechanisms, competition, can high mortality rates be considered to be a relatively direct consequence of high NPP. The remaining mechanisms force us to adopt a different view of causality, in which tree growth rates and probability of mortality can vary with at least a degree of independence along productivity gradients. In many cases, rather than being a direct cause of high mortality rates, NPP may remain high in spite of high mortality rates. The independent influence of plant enemies and other factors helps explain why forest biomass can show little correlation, or even negative correlation, with forest NPP.

Co-variation of life history characters in the family Lophoziaceae: a multivariate analysis

The particular combinations of life history traits that organisms display are a product of trade-offs between conflicting demands on finite energy budgets. Organisms are, therefore, expected to display combinations of co-evolved life history traits, sometimes referred to as tactics or strategies, that overall maximize fitness within the constraints imposed by environmental and/or genetic limitations. This study uses a combination of Principal Component and Cluster analyses to examine patterns of life history co-variation in the family Lophoziaceae, based on data obtained from literature. We also evaluate the relationship between sexuality, reproductive mode and sporophyte/gemma frequency among members of this family. The species studied are resolved into more or less coherent groups that have specific life history trait combinations. No evidence of either phylogenetic constraint or close relationship to habitat parameters could be demonstrated. The results suggest trade-offs between spore frequency and gemma frequency. Dioicous species dominate the family, with about 90% of the species being dioicous. The relationship between sexuality and sporophyte frequency is statistically significant: monoicous species produce sporophytes more frequently than dioicous species. Mode of reproduction and gemmae production were both independent of sexuality. For species that can reproduce both ways, sexuality was independent of diaspore frequency. The data are consistent with the idea of coevolved life history “strategies” as in most others organisms studied.

Putting phylogeny into the analysis of biological traits: A methodological approach

Phylogenetic comparative methods have long considered phylogenetic signal as a source of statistical bias in the correlative analysis of biological traits. However, the main life-history strategies existing in a set of taxa are often combinations of life history traits that are inherently phylogenetically structured. In this paper, we present a method for identifying evolutionary strategies from large sets of biological traits, using phylogeny as a source of meaningful historical and ecological information. Our methodology extends a multivariate method developed for the analysis of spatial patterns, and relies on finding combinations of traits that are phylogenetically autocorrelated. Using extensive simulations, we show that our method efficiently uncovers phylogenetic structures with respect to various tree topologies, and remains powerful in cases where a large majority of traits are not phylogenetically structured. Our methodology is illustrated using empirical data, and implemented in the adephylo package for the free software R.

Sensitivity of plant functional types to climate change: classification tree analysis of a simulation model

Question: The majority of studies investigating the impact of climate change on local plant communities ignores changes in regional processes, such as immigration from the regional seed pool. Here we explore: (i) the potential impact of climate change on composition of the regional seed pool, (ii) the influence of changes in climate and in the regional seed pool on local community structure, and (iii) the combinations of life history traits, i.e. plant functional types (PFTs), that are most affected by environmental changes. Location: Fire-prone, Mediterranean-type shrublands in southwestern Australia. Methods: Spatially explicit simulation experiments were conducted at the population level under different rainfall and fire regime scenarios to determine the effect of environmental change on the regional seed pool for 38 PFTs. The effects of environmental and seed immigration changes on local community dynamics were then derived from community-level experiments. Classification tree analyses were used to investigate PFT-specific vulnerabilities to climate change. Results: The classification tree analyses revealed that responses of PFTs to climate change are determined by specific trait characteristics. PFT-specific seed production and community patterns responded in a complex manner to climate change. For example, an increase in annual rainfall caused an increase in numbers of dispersed seeds for some PFTs, but decreased PFT diversity in the community. Conversely, a simulated decrease in rainfall reduced the number of dispersed seeds and diversity of PFTs. Conclusions: PFT interactions and regional processes must be considered when assessing how local community structure will be affected by environmental change.

Life-history tactics of brooding Crustacea

Results of studies on the population biologies of five species of brooding crustaceans, four amphipods and a myodocopid ostracod, from an unpredictable habitat at Kaikoura, New Zealand, provide a test of current theories of life-history tactics. Sediment depths inhabited provided a ranking of species habitat stabilities and mortality risks, both greatest at the sand surface. Population parameters confirm the ranking, but comparisons with species' combinations of life-history traits do not fit predictions of the various theories. The failure of these theories is principally due to phylogenetic constraints, the lack of viable genetic alternatives for a trait. A new theory is required, one that encompasses phylogenetic constraints and correlations of some traits with body size. Such a theory must recognize the possibility of several equally successful combinations of traits in a given situation and incorporate recent ideas on growth rates, body size and size-specific mortality.

The Evolution of Life History Traits: A Critique of the Theory and a Review of the Data

In 1976, I reviewed (84) two models which give alternative explanations for the adaptation of life history traits to stable and fluctuating environments. Deterministic models (rand Kselection) predict that organisms exposed to high levels of densityindependent mortality, wide fluctuations in population density, or repeated episodes of colonization will evolve towards a combination of earlier maturity, larger broods, higher reproductive effort, and shorter lifespans than will organisms exposed to density-dependent mortality or constant population density (48, 65). Stochastic models (58, 77) predict the evolution of the same combinations of life history traits, but for different reasons: when fluctuations in the environment result in highly variable juvenile mortality, then a syndrome of delayed maturity, smaller reproductive effort, and greater longevity should evolve. Several years ago I set out to test these predictions by measuring the reproductive traits of two species of small fish that had been introduced to Hawaiian reservoirs in 1907 and 1922. Ambiguities appeared in the interpretation of the results, some of them inherent in the theory, others in the observations. I could not decide which of several possible causal systems had produced the pattern I observed. To determine what my results meant, I first tried to understand what life history data could mean in general, given the present state of our knowledge. In brief, the theory is not yet refined enough to be tested by crucial experiments that can pinpoint flaws. Under these circumstances, observation and experiment cannot falsify predictions definitively, but they can profitably arbitrate among the various simplifying assumptions that theorists may want to try out in their pursuit of unambiguous predictions that cleanly touch reality.