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•Stable isotopes are increasingly used tool of biologists.•Researchers often assume that isotopic properties are thermally static.•Temperature increased incorporation rates via higher ...growth and catabolism rates.•Temperature decreases trophic fractionation.•Natural variation in temperature must be accounted for when using stable isotopes.
Stable isotopes are valuable tools in physiological and ecological research, as they can be used to estimate diet, habitat use, and resource allocation. However, in most cases a priori knowledge of two key properties of stable isotopes is required, namely their rate of incorporation into the body (incorporation rate) and the change of isotope values between consumers and resources that arises during incorporation of the isotopes into the consumer’s tissues (trophic discrimination). Previous studies have quantified these properties across species and tissue types, but little is known about how they vary with temperature, a key driver of many biological rates and times. Here, we explored for the first time how temperature affects both carbon incorporation rate and trophic discrimination via growth rates, using the domestic cricket, Acheta domesticus. We raised crickets at 16 °C, 21 °C, and 26 °C and showed that temperature increased carbon isotope incorporation rate, which was driven by both an increased growth rate and catabolism at higher temperatures. Trophic discrimination of carbon isotopes decreased at higher temperatures, which we attributed to either lower activation energies needed to synthesize non-essential amino acids at higher temperatures or the increased utilization of available resources of consumers at higher temperatures. Our results demonstrate that temperature is a key driver of both carbon isotope incorporation rate and trophic discrimination, via mechanisms that likely persist across all ectotherms. Experiments to determine incorporation rates and trophic discrimination factors in ectotherms must include temperature as a major factor, and natural variation in temperature might have significant effects on these isotopic properties that then can affect inferences made from isotope values.
Life history scaling in a tropical forest Grady, John M.; Read, Quentin D.; Record, Sydne ...
The Journal of ecology,
March 2024, 2024-03-00, 20240301, Letnik:
112, Številka:
3
Journal Article
Recenzirano
Both tree size and life history variation drive forest structure and dynamics, but little is known about how life history frequency changes with size. We used a scaling framework to quantify ...ontogenetic size variation and assessed patterns of abundance, richness, productivity and light interception across life history strategies from >114,000 trees in a primary, neotropical forest. We classified trees along two life history axes: a fast–slow axis characterized by a growth–survival trade‐off, and a stature–recruitment axis with tall, long‐lived pioneers at one end and short, short‐lived recruiters at the other.
Relative abundance, richness, productivity and light interception follow an approximate power law, systematically shifting over an order of magnitude with tree size. Slow saplings dominate the understorey, but slow trees decline to parity with rapidly growing fast and long‐lived pioneer species in the canopy.
Like the community as a whole, slow species are the closest to obeying the energy equivalence rule (EER)—with equal productivity per size class—but other life histories strongly increase productivity with tree size. Productivity is fuelled by resources, and the scaling of light interception corresponds to the scaling of productivity across life history strategies, with slow and all species near solar energy equivalence. This points towards a resource‐use corollary to the EER: the resource equivalence rule.
Fitness trade‐offs associated with tree size and life history may promote coexistence in tropical forests by limiting niche overlap and reducing fitness differences.
Synthesis. Tree life history strategies describe the different ways trees grow, survive and recruit in the understorey. We show that the proportion of trees with a pioneer life history strategy increases steadily with tree size, as pioneers become relatively more abundant, productive, diverse and capture more resources towards the canopy. Fitness trade‐offs associated with size and life history strategy offer a mechanism for coexistence in tropical forests.
Resumen
Tanto el tamaño de los árboles como la variación demográfica determinan la estructura y la dinámica de los bosques, pero se sabe poco sobre cómo cambia la frecuencia de diferentes estrategias demográficas con el tamaño de los árboles. Utilizamos un marco de escala para cuantificar como abundancia, riqueza de especies, productividad e interceptación cambian con el tamaño a lo largo de las estrategias demográficas de > 114.000 árboles en un bosque neotropical primario. Clasificamos los árboles a lo largo de dos ejes demográficas: un eje rápido‐lento caracterizado por un compromiso crecimiento‐supervivencia, y un eje estatura‐reclutamiento con pioneros de larga vida y gran estatura en un extremo y reclutadores de corta vida y baja estatura en el otro.
La abundancia relativa, la riqueza de especies, la productividad leñosa y la interceptación de la luz siguen una aproximada ley de potencia, cambiando sistemáticamente en un orden de magnitud con el tamaño del árbol. Los individuos pequeños lentos dominan el sotobosque, pero disminuyen a paridad con las especies pioneras de crecimiento rápido y larga vida en el dosel.
Al igual que la comunidad en su conjunto, las especies lentas son las que más se acercan a la regla de equivalencia energética (REE)—caracterizado por igual productividad por clase de tamaño—pero las otras estrategias demográficas aumentan fuertemente la productividad con el tamaño del árbol. La productividad depende de la luz, y la escala de interceptación de la luz coincide con la escala de productividad a través de las estrategias demográficas, con las especies lentas y todas las especies cerca de la equivalencia de energía solar. Esto apunta hacia un corolario de uso de recursos de la REE: la regla de equivalencia de recursos.
Las compensaciones de la historia vital con el tamaño pueden promover la coexistencia en los bosques tropicales limitando el solapamiento de nichos y reduciendo las diferencias de aptitud.
Síntesis: Las estrategias demográficas de los árboles describen las diferentes formas en que los árboles crecen, sobreviven y se reclutan en el sotobosque. Demostramos que la proporción de árboles de una determinada estrategia demográfica cambia sistemáticamente con el tamaño del árbol, dando lugar a los correspondientes cambios en los patrones de diversidad, energía y uso de recursos desde el suelo del bosque hacia el dosel. Las compensaciones entre historia vital y tamaño ofrecen un mecanismo para la coexistencia en los bosques tropicales.
Tree life history strategies describe the different ways trees grow, survive and recruit in the understorey. We show that the proportion of trees with a pioneer life history strategy increases steadily with tree size, as pioneers become relatively more abundant, productive, diverse and capture more resources towards the canopy. Fitness trade‐offs associated with size and life history strategy offer a mechanism for coexistence in tropical forests.
Recognition that intermittent pools are a single habitat phase of an intermittent pool bed that cycles between aquatic and terrestrial habitat greatly enhances their usefulness for addressing general ...questions in ecology. The aquatic phase has served as a model system in many ecological studies, because it has distinct habitat boundaries in space and time and is an excellent experimental system, but the aquatic to terrestrial transition and terrestrial phase remain largely unstudied. We conducted a field experiment within six replicate natural intermittent pool beds to explore macroinvertebrate community dynamics during the transition from aquatic to terrestrial habitat and during the terrestrial phase. We monitored and compared macroinvertebrate communities within leaf packs that i) remained wet, ii) underwent drying (i.e., started wet and then dried), and iii) remained dry. Our results show that i) a diverse macroinvertebrate community inhabits all phases of intermittent pool beds, ii) pool drying involves colonization by an assemblage of macroinvertebrates not recorded in permanently terrestrial leaf packs, iii) the community within dried leaf packs remains distinct from that of permanently terrestrial leaf packs for an extended period following drying (possibly until subsequent refilling), and iv) there are likely to be strong spatial and temporal resource linkages between the aquatic and terrestrial communities. The unique environmental characteristics of intermittent pool beds, which repeatedly cycle from aquatic to terrestrial habitat, should continue to make them valuable study systems.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Body Size Dependence of Trophic Cascades DeLong, John P.; Gilbert, Benjamin; Shurin, Jonathan B. ...
The American naturalist,
03/2015, Letnik:
185, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Trophic cascades are indirect positive effects of predators on resources via control of intermediate consumers. Larger-bodied predators appear to induce stronger trophic cascades (a greater rebound ...of resource density toward carrying capacity), but how this happens is unknown because we lack a clear depiction of how the strength of trophic cascades is determined. Using consumer resource models, we first show that the strength of a trophic cascade has an upper limit set by the interaction strength between the basal trophic group and its consumer and that this limit is approached as the interaction strength between the consumer and its predator increases. We then express the strength of a trophic cascade explicitly in terms of predator body size and use two independent parameter sets to calculate how the strength of a trophic cascade depends on predator size. Both parameter sets predict a positive effect of predator size on the strength of a trophic cascade, driven mostly by the body size dependence of the interaction strength between the first two trophic levels. Our results support previous empirical findings and suggest that the loss of larger predators will have greater consequences on trophic control and biomass structure in food webs than the loss of smaller predators.
Although average, species-level interaction strength plays a key role in driving population dynamics and community structure, predator-prey interactions occur among individuals. As a result, ...individual variation in foraging rates may play an important role in determining the effects of predator-prey interactions on communities. Such variation in foraging rates stems from individual variation in traits that influence the mechanistic components of the functional response, such as movements that determine encounters and behaviors such as decisions to attack. However, we still have little information about individual-level variation in functional responses or the traits that give rise to such variation. Here we combine a standard functional response experiment with wolf spiders foraging on fruit flies with a novel analysis to connect individual morphology, physiology, and movement to individual foraging performance. We found substantial variation in traits between males and females, but these were not clearly linked to the differences in the functional response between males and females. Contrary to expectations, we found no effect of body velocity, leg length, energetic state, or metabolic rate on foraging performance. Instead, we found that body mass interacted with body rotations (clockwise turns), such that larger spiders showed higher foraging performance when they turned more but the reverse was true for smaller spiders. Our results highlight the need to understand the apparent complexity of the links between the traits of individuals and the functional response.
•The ecological and taxonomic diversity of insects make them ideal study systems.•Body size is a key trait of insects, impacting many aspects of their ecology.•By influencing movement and behavior, ...size impacts trophic interaction strength.•Body-size research should further incorporate behavioral ecology, linking individuals to communities.•The resultant quantitative framework will have significant basic and applied benefits.
The role of body size as a key feature determining the biology and ecology of individual animals, and thus the structure and dynamics of populations, communities, and ecosystems, has long been acknowledged. Body size provides a functional link between individual-level processes such as physiology and behavior, with higher-level ecological processes such as the strength and outcome of trophic interactions, which regulate the flow of energy and nutrients within and across ecosystems. Early ecological work on size in animals focused on vertebrates, and especially mammals. More recent focus on invertebrates, and insects in particular, that spans levels of organization from individual physiology to communities, has greatly expanded and improved our understanding of the role of body size in ecology. Progress has come from theoretical advances, from the production of new, high-resolution empirical data sets, and from enhanced computation and analytical techniques. Recent findings suggest that many of the allometric concepts and principles developed over the last century also apply to insects. But these recent studies also emphasize that while body size plays a crucial role in insect ecology, it is not the entire story, and a fuller understanding must come from an approach that integrates both size and non-size effects. In this review we discuss the core principles of a size-based (allometric) approach in insect ecology, together with the potential of such an approach to connect biological processes and mechanisms across levels of organization from individuals to ecosystems. We identify knowledge gaps, particularly related to size constraints on insect movement and behavior, which can impact the strength and outcome of species interactions (and especially trophic interactions) and thus link individual organisms to communities and ecosystems. Addressing these gaps should facilitate a fuller understanding of insect ecology, with important basic and applied benefits.
Understanding constraints on consumer-resource body size-ratios is fundamentally important from both ecological and evolutionary perspectives. By analyzing data on 4,685 consumer-resource ...interactions from nine ecological communities, we show that in spatially complex environments—where consumers can forage in both two (2D, e.g., benthic zones) and three (3D, e.g., pelagic zones) spatial dimensions—the resource-to-consumer body size-ratio distribution tends toward bimodality, with different median 2D and 3D peaks. Specifically, we find that median size-ratio in 3D is consistently smaller than in 2D both within and across communities. Furthermore, 2D and 3D size (not size-ratio) distributions within any community are generally indistinguishable statistically, indicating that the bimodality in size-ratios is not driven simply by a priori size-segregation of species (and therefore, interactions) by dimensionality, but due to other factors. We develop theory that correctly predicts the direction and magnitude of these differences between 2D and 3D size-ratio distributions. Our theory suggests that community-level size-ratio bimodality emerges from the stronger scaling of consumption rate with size in 3D interactions than in 2D which both, maximizes consumer fitness, and allows coexistence, across a larger range of size-ratios in 3D. We also find that consumer gape-limitation can amplify differences between 2D and 3D size-ratios, and that for either dimensionality, higher carrying capacity allows coexistence of a wider range of size-ratios. Our results reveal new and general insights into the size structure of ecological communities, and show that spatial complexity of the environment can have far reaching effects on community structure and dynamics across scales of organization.
Summary
Global warming and habitat fragmentation impose dramatic and potentially interactive impacts on ecosystems. Warming induces shifts in species' distributions as they track temperature changes, ...but this can be hindered in fragmented landscapes. Corridors connecting habitat patches might ameliorate the combined effects of fragmentation and global warming.
Using novel automated tracking methods, the movement of woodlice (Oniscus asellus) ranging in body size from 15·3 to 108·6 mg was quantified across a temperature range from 15 to 25 °C as they moved around an experimental fragmented landscape. We used confirmatory path analysis to test causal effects of temperature and body size on individual movement and corridor crossing rates between two habitat patches.
Results showed that woodlice behaved differently in corridors than patches by moving, on average, faster and more often. This is congruent with natural systems where corridors generally provide lower quality habitat than patches. Although metabolic theory suggests positive scaling of movement with body temperature (up to a peak) and body size, we found that corridor crossing rate was (i) not directly affected by body size and (ii) negatively influenced by temperature, possibly due to its indirect effects via humidity.
Our path model revealed that metabolic scaling could only explain temperature effects on maximum body velocity, but decision‐based behaviour explained most variation in corridor crossing rates. This led to direct and indirect effects of temperature and size on individual movement between habitat patches.
Our findings suggest that increasing mean global temperatures, coupled with increasing habitat fragmentation, could have synergistic negative impacts on populations through a combination of physiological and behavioural factors that mediate individual responses to temperature and fragmentation.
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