Seasonal Ecosystems Research Articles

Seasonality Structures Avian Functional Diversity and Niche Packing Across North America.

Assemblages in seasonal ecosystems undergo striking changes in species composition and diversity across the annual cycle. Despite a long-standing recognition that seasonality structures biogeographic gradients in taxonomic diversity (e.g., species richness), our understanding of how seasonality structures other aspects of biodiversity (e.g., functional diversity) has lagged. Integrating seasonal species distributions with comprehensive data on key morphological traits for bird assemblages across North America, we find that seasonal turnover in functional diversity increases with the magnitude and predictability of seasonality. Furthermore, seasonal increases in bird species richness led to a denser packing of functional trait space, but functional expansion was important, especially in regions with higher seasonality. Our results suggest that the magnitude and predictability of seasonality and total productivity can explain the geography of changes in functional diversity with broader implications for understanding species redistribution, community assembly and ecosystem functioning.

Flowering phenology influences butterfly nectar foraging on non-native plants in an oak savanna.

The negative impacts of non-native species have been well documented, but some non-natives can play a positive role in native ecosystems. One way that non-native plants can positively interact with native butterflies is by provisioning nectar. Relatively little is known about the role of phenology in determining native butterfly visitation to non-native plants for nectar, yet flowering time directly controls nectar availability. Here we investigate the phenological patterns of flowering by native and non-native plants and nectar foraging by native butterflies in an oak savanna on Vancouver Island, British Columbia, Canada. We also test whether native butterflies select nectar sources in proportion to their availability. We found that non-native plants were well integrated into butterfly nectar diets (83% of foraging observations) and that visitation to non-natives increased later in the season when native plants were no longer flowering. We also found that butterflies selected non-native flowers more often than expected based on their availability, suggesting that these plants represent a potentially valuable resource. Our study shows that non-native species have the potential to drive key species interactions in seasonal ecosystems. Management regimes focused on eradicating non-native species may need to reconsider their aims and evaluate resources that non-natives provide.

Cerambycid Beetle Communities in Caatinga Dry Forests Are Structured by Seasonal Species Turnover

Dry forests in the Caatinga biome of Brazil are seasonal ecosystems where diversity is driven by water availability. Understanding how the distribution of communities is driven by temporal climate changes has intrigued researchers for decades. However, temporal diversity patterns should be more evident in dry environments, since seasonality is characterized by being highly limiting to insect activities. Cerambycid beetles are considered good ecological indicators because they respond well to impacts of environmental changes. Thus, we asked two questions: (i) How do climatic changes affect the diversity of these insects across seasons? (ii) Are diversity components correlated with increasing air humidity, rainfall, and temperature? Our results showed a marked seasonality of cerambycid beetles, with higher abundance and richness in the wet season. The mean temperature and relative humidity were predictors of the composition of beetle assemblages. However, the variation of cerambycid assemblages between seasons is related mainly to species turnover. Our study demonstrates that the combined effect of temperature and humidity drives the temporal distribution of the cerambycids in dry forests. Although thermal sensitivity was low, the decrease in air moisture during the dry season was the limiting factor for these insects. Species turnover increased continuously with air moisture and temperature rise, creating temporal segregation among cerambycid species and maintaining the stability of the assemblage. Thus, our results are consistent with mechanisms invoking activity patterns, desiccation resistance, and physiologic constraints that predict a decrease in richness and abundance of the cerambycids from warmer and moister to colder and drier conditions.

Seasonal variation of leaf thickness: An overlooked component of functional trait variability.

The dry and wet seasons in the Neotropics have strong effects on soil water and nutrient availability, as well as on forest dynamics. Despite these major effects on forest ecology, little is known on how leaf traits vary throughout the seasons in tropical rainforest trees. Here, we investigated the influence of seasonal variations in climate and soil characteristics on leaf trait variation in two tropical tree species. We measured two leaf traits, thickness and water mass per area, in 401 individuals of two species of Symphonia (Clusiaceae) in the Paracou research station in French Guiana tropical lowland rainforest. We found a significant effect of seasonal variation on these two leaf traits. Soil relative extractable water was a strong environmental predictor of leaf trait variation in response to seasonal variation. Reduced soil water availability during the dry season was associated with increased leaf thickness and water mass per area, possibly as a result of stomatal closure. Our findings advocate the need to account for environmental seasonality when studying leaf traits in seasonal ecosystems such as tropical forests.

Human Food Dynamics in Highly Seasonal Ecosystems: A Case Study of Plant-Eating in Riverine Communities in Central Amazon

Food habit studies in the Amazon emphasize the consumption of fish and manioc (Manihot esculenta) flour as basic diet in different ethnic groups, while little is known about human plant-related diet dynamics during the hydrological regime. In a scenario of food transition in rural Amazonia, with insertion of industrialized items in the diet, traditional food and consumption of regional products have undergone transformations, affecting the autonomy and lifestyle of traditional populations. Considering this, the objectives of the current case study were: (1) to contextualize plant-related eating habits in five Riverine communities on the Lower Purus River and (2) to characterize the dietary dynamics of plant eating according to the hydrological regime, considering the provenance of food items. We conducted interviews and sample collection in both low- and high-water seasons. We calculated species richness and diversity per meal and season and used multivariate analysis to access differences in plant consumption between seasons. The greatest richness and diversity of plants is consumed in the flooding season and mainly as snacks, the meal most susceptible to being replaced by industrialized foods. Despite a significant difference in diet between seasons, the basic array of plants consumed is similar in both seasons, with availability topped up by external purchases. This tendency deserves attention and action from public policies aimed at providing food security in the region.

Can Grazing Moderate Climatic Effects on Herbage Nutritional Quality?

In Mediterranean grasslands, the composition of vegetation and its nutritional quality for animals are strongly affected by the climatic conditions prevailing during winter and spring. Therefore, these seasonal ecosystems provide an opportunity to examine how variability in climatic conditions affects the regeneration and quality of pasture vegetation. The intensity of grazing in this seasonal system can moderate, or alternatively exacerbate, climatic effects on the nutritional quality of the vegetation. Herein, we analyzed the interactive effects of climate variables, grazing intensity, and grazing exclusion on herbage quality parameters using long-term vegetation and climate data collected during 2005–2018 from an extensive experiment in Galilee, Israel. We evaluated the contribution of different climate variables to the prediction of herbage quality parameters. Our results showed that climate variables have a dramatic effect on herbage quality and that this effect interacts with grazing intensity. Herbage quality improved in temperate rainy years compared to warm and dry years. High grazing intensity improved herbage quality under temperate climate conditions, but this effect was moderated or completely disappeared as winter conditions become warmer and drier. The results of the study foresee negative effects of warming and drying on the carrying capacity of natural pastures.

Data on litterfall production and meteorology at an old-growth tropical dry forest in northwestern Mexico.

Chronological measurements of litterfall production can be used for understanding ecosystem dynamics such as net primary production and carbon cycling in highly seasonal ecosystems such as tropical dry forests (TDF). This paper presents data on litterfall production and meteorology in an old-growth TDF. The data was generated within the Monte Mojino Reserve located in the Sierra de Alamos – Rio Cuchujaqui Natural Protected Area in northwestern México. For litterfall collection, twenty randomly placed litterfall traps were installed to collect monthly litterfall production across four full growing seasons (48 monthly collections). Meteorological data were obtained from an automatic micrometeorological station that recorded data in situ from January 2013 to March 2019. The database includes litterfall production [g m−2 month−1], monthly rainfall [mm], air temperature [°C], relative humidity [%] and photosynthetic active radiation [µmol m−2 s−1].

A long-term assessment of fire regimes in a Brazilian ecotone between seasonally dry tropical forests and savannah

Abstract Fire is a recurrent phenomenon in semiarid seasonal ecosystems. The study of the relationship between fire and climate could provide new approaches for understanding fire dynamics in semiarid regions, which could be useful for strategically managing the loss and recovery of natural resources under threat. Here, we evaluated the patterns of fires occurrence in a semiarid Caatinga-Cerrado ecotone in the Northeast Region of Brazil by characterizing their spatiotemporal dynamics associated with climatic conditions. Using a temporal series of 306 Landsat images, we mapped a burned area database at a fine spatial resolution (30 m) from 1999 to 2017 in the Capivara-Confusoes Mosaic of protected areas and their surroundings. Fire seasonality was analyzed through climatic seasons, distinguishing between the rainy season (RS), early dry season (EDS), middle dry season (MDS) and late dry season (LDS), by analysis of the daily precipitation of ground-based stations in the area. We created yearly, seasonal and recurrence maps of burned areas to assess fire regimes. The results showed that the 48% of the area was burned during the 19-year long period considered. Serra das Confusoes National Park (SCoNP) had 302,644 ha burned, Serra da Capivara National Park (SCaNP) had 2056 ha burned and the ecological corridor had 215,718 ha burned. Most of the burned area was registered during the MDS (36% of the study area), there was almost no burned area in the EDS (

Seasonal use of waterholes and pathways by macrofauna in the dry forest of Costa Rica

AbstractTemporal and spatial scarcity of water in semi-arid and seasonal ecosystems often leads to changes in movements and behaviour of large vertebrates, and in the neotropics this dynamic is poorly understood due to logistical and methodological limitations. Here we used camera trapping to elucidate variation in patterns of seasonal use of waterholes and pathways by 10 large-mammal and four large-bird species in the dry forest of north-western Costa Rica. From 2011 to 2015, we deployed trail cameras at 50 locations, including waterholes and three types of pathway (roads, human trails and animal paths). We used Generalized Linear Models to evaluate the effect of location and seasonality on the rates at which independent photographs were taken. We found interacting effects of location and seasonality for the capuchin monkey (Cebus capucinus), the tiger heron (Trigrisoma mexicanum), the white-tailed deer (Odocoileus virginianus) and the tapir (Tapirus bairdii) suggesting that these species were the most influenced by waterholes during the dry season. Comparison of waterhole sites and specific types of pathways (roads, animal paths and human trails) showed that location influenced photo-capture rates of almost all species, suggesting a useful insight to avoid and account for bias in camera trap studies. Furthering our ecological understanding of seasonal water regimes and large vertebrates’ behaviours allow for better understanding of the consequences of climate change on them.

Seed predation increases from the Arctic to the Equator and from high to low elevations.

Species interactions have long been predicted to increase in intensity toward the tropics and low elevations because of gradients in climate, productivity, or biodiversity. Despite their importance for understanding global ecological and evolutionary processes, plant-animal interaction gradients are particularly difficult to test systematically across large geographic gradients, and evidence from smaller, disparate studies is inconclusive. By systematically measuring postdispersal seed predation using 6995 standardized seed depots along 18 mountains in the Pacific cordillera, we found that seed predation increases by 17% from the Arctic to the Equator and by 17% from 4000 meters above sea level to sea level. Clines in total predation, likely driven by invertebrates, were consistent across treeline ecotones and within continuous forest and were better explained by climate seasonality than by productivity, biodiversity, or latitude. These results suggest that species interactions play predictably greater ecological and evolutionary roles in tropical, lowland, and other less seasonal ecosystems.

Temporal variation in plant–pollinator networks from seasonal tropical environments: Higher specialization when resources are scarce

Abstract The temporal dynamics of plant phenology and pollinator abundance across seasons should influence the structure of plant–pollinator interaction networks. Nevertheless, such dynamics are seldom considered, especially for diverse tropical networks. Here, we evaluated the temporal variation of four plant–pollinator networks in two seasonal ecosystems in Central Brazil (Cerrado and Pantanal). Data were gathered on a monthly basis over 1 year for each network. We characterized seasonal and temporal shifts in plant–pollinator interactions, using temporally discrete networks. We predicted that the greater floral availability in the rainy season would allow for finer partitioning of the floral niche by the pollinators, i.e. higher specialization patterns as previously described across large spatial gradients. Finally, we also evaluated how sampling restricted to peak flowering period may affect the characterization of the networks. Contrary to our expectations, we found that dry season networks, although characterized by lower floral resource richness and abundance, showed higher levels of network‐wide interaction partitioning (complementary specialization and modularity). For nestedness, though, this between‐seasons difference was not consistent. Reduced resource availability in the dry season may promote higher interspecific competition among pollinators leading to reduced niche overlap, thus explaining the increase in specialization. There were no consistent differences between seasons in species‐level indices, indicating that higher network level specialization is an emergent property only seen when considering the entire network. However, bees presented higher values of specialization and species strength in relation to other groups such as flies and wasps, suggesting that some plant species frequently associated with bees are used only by this group. Our study also indicates that targeted data collection during peak flowering generates higher estimates of network specialization, possibly because species activity spans longer periods than the targeted time frame. Hence, depending on the period of data collection, different structural values for the networks of interactions may be found. Synthesis. Plant–pollinator networks from tropical environments have structural properties that vary according to seasons, which should be taken into account in the description of the complex systems of interactions between plants and their pollinators in these areas.

Seasonal dynamics of avian guilds inside and outside core protected areas in an Andean Biosphere Reserve of southern Chile

ABSTRACTCapsule: Many protected forests at high elevations show higher endemic biodiversity than unprotected habitats at low elevations. In seasonal ecosystems, however, harsh environmental conditions during winter may force individuals to move from protected forests to unprotected degraded forests in lowlands.Aims: To examine how forest types and seasons affect avian diversity and habitat-use guilds in protected and unprotected forests.Methods: Habitat and seasonal avian surveys were conducted to test forest type and seasonal differences on avian species richness, relative abundances and relative abundance of habitat-use guilds.Results: Twenty-three avian species (∼40% endemics) were recorded. Highland old growth forests showed the highest richness (4.1–4.9 species/point count). The lowest richness was recorded in mid-elevation secondary forests (3.1 species/point count). The highest relative abundances for habitat-specialist understorey users and large tree users were recorded in highland old growth forests. However, the abundance of large tree users was higher in secondary forests at low elevations during colder seasons.Conclusions: Some species and guilds may move to lower elevations outside protected areas during winter. Increasing degradation of unprotected areas will likely affect the suitability of ‘winter habitat’ for specialist guilds, and thus the ecological processes and source/sink dynamics occurring across boundaries of protected and unprotected areas.

Use of remote cameras to evaluate ocelot (Leopardus pardalis) population parameters in seasonal tropical dry forests of central-western Mexico

AbstractThe ocelot is one of the most studied felid species in the neotropics yet most of our current knowledge comes from tropical rain forests and protected areas. Therefore, we lack a comprehensive understanding on how the species abundance varies in terms of ecological parameters across its full distribution range. This is particularly true for the species population in the Northern Hemisphere, as data of ocelot populations occurring in tropical dry forests are scarce. In this study, we focused on: a) generating population data (density and sex ratios), based on camera-trapping, for ocelot occurring in the vast and understudied tropical dry forest of the western Pacific of Mexico. b) Comparing the variation in species abundance and density across its distribution range, including a larger set of studies from the Northern Hemisphere, contrasting parameters between rain forests and tropical seasonal ecosystems and re-examining the assumed relationship between precipitation and ocelot abundance. Overall, we identified 17 ocelots in our study sites and estimated an average density of 23.7 individuals (ind) per 100 km2with a female to male ratio >1. No significant differences in ocelot density was found between seasonal tropical forests and rain forests studies (Wilcoxon test, W=71, p=0.7675). Moreover, we found no support for the relation between ocelot density and precipitation (only when restricting our analysis to rain forest data the fit of the regression model was close to be significant, R2=0.2463, p=0.07107). Our results indicate that tropical seasonal ecosystems and dry forest in particular, may present ocelot population with similar levels of abundance than tropical rain forests. We observed that precipitation is a poor predictor of ocelot abundance. In our study, we observed that overall local ecological factors (e.g. prey abundance and interspecific interactions) influenced the spatial and temporal abundance of ocelots.

Differences in the sensitivity of fungi and bacteria to season and invertebrates affect leaf litter decomposition in a Mediterranean stream.

Microorganisms are key drivers of leaf litter decomposition; however, the mechanisms underlying the dynamics of different microbial groups are poorly understood. We investigated the effects of seasonal variation and invertebrates on fungal and bacterial dynamics, and on leaf litter decomposition. We followed the decomposition of Populus nigra litter in a Mediterranean stream through an annual cycle, using fine and coarse mesh bags. Irrespective of the season, microbial decomposition followed two stages. Initially, bacterial contribution to total microbial biomass was higher compared to later stages, and it was related to disaccharide and lignin degradation; in a later stage, bacteria were less important and were associated with hemicellulose and cellulose degradation, while fungi were related to lignin decomposition. The relevance of microbial groups in decomposition differed among seasons: fungi were more important in spring, whereas in summer, water quality changes seemed to favour bacteria and slowed down lignin and hemicellulose degradation. Invertebrates influenced litter-associated microbial assemblages (especially bacteria), stimulated enzyme efficiencies and reduced fungal biomass. We conclude that bacterial and fungal assemblages play distinctive roles in microbial decomposition and differ in their sensitivity to environmental changes, ultimately affecting litter decomposition, which might be particularly relevant in highly seasonal ecosystems, such as intermittent streams.

Strategies in nitrogen uptake and use by deciduous and evergreen woody species in a seasonally dry sandhill community

Dry seasonal ecosystems such as the Florida sandhill are defined by a pronounced and consistent dry season that results in both water and nutrient limitation. Deciduous and evergreen species have evolved different leaf phenologies, which change the temporal pattern of nutrient demands for leaf growth. To measure N uptake for deciduous and evergreen species during late dry season deciduous leaf-out, we labeled the shallow soil with 15N by spreading a mixture of native sand and 15N-KNO3 around each tree and measured foliar nitrogen isotopic composition. We also measured foliar N content and nitrogen resorption efficiency (NRE). Evergreen and deciduous species were not consistently different in foliar N content and NRE, but natural foliar δ15N values were consistently higher in deciduous species. Labeling experiments show that uptake rate of 15N- labeled NO3 − was lowest for the deciduous species. Inconsistent results in foliar N content and NRE do not explain the differences in leaf habit in nutrient-poor ecosystems. Low N uptake during leaf-out limits deciduous species to the most fertile regions of the Florida scrub as well as in several other ecosystems, so that they can take up sufficient N to meet the demands of leaf growth.

Dietary overlap and seasonality in three species of mormoopid bats from a tropical dry forest.

Competing hypotheses explaining species' use of resources have been advanced. Resource limitations in habitat and/or food are factors that affect assemblages of species. These limitations could drive the evolution of morphological and/or behavioural specialization, permitting the coexistence of closely related species through resource partitioning and niche differentiation. Alternatively, when resources are unlimited, fluctuations in resources availability will cause concomitant shifts in resource use regardless of species identity. Here, we used next-generation sequencing to test these hypotheses and characterize the diversity, overlap and seasonal variation in the diet of three species of insectivorous bats of the genus Pteronotus. We identified 465 prey (MOTUs) in the guano of 192 individuals. Lepidoptera and Diptera represented the most consumed insect orders. Diet of bats exhibited a moderate level of overlap, with the highest value between Pteronotus parnellii and Pteronotus personatus in the wet season. We found higher dietary overlap between species during the same seasons than within any single species across seasons. This suggests that diets of the three species are driven more by prey availability than by any particular predator-specific characteristic. P.davyi and P.personatus increased their dietary breadth during the dry season, whereas P.parnellii diet was broader and had the highest effective number of prey species in all seasons. This supports the existence of dietary flexibility in generalist bats and dietary niche overlapping among groups of closely related species in highly seasonal ecosystems. Moreover, the abundance and availability of insect prey may drive the diet of insectivores.

Seed reserve translocation and early seedling growth of eight tree species in a tropical deciduous forest in Mexico

Seed reserves play an essential role during germination and seedling establishment and are particularly important for species that grow in seasonal ecosystems with a short growing season. In this study, we examined (a) how and when the seedlings change their dependence from seed resources to external resources, (b) the lipid, nitrogen, and non-structural carbohydrate reserve translocation from seeds to seedlings over time, and (c) whether reserve translocation may be correlated to cotyledon and leaf lifespan of seedlings for eight tree species in a tropical deciduous forest in north-western Mexico. Our results showed that the cotyledon lifespan was not related to the cotyledon type (photosynthetic or reserve) and that the cotyledon biomass did not decrease significantly until germination. In six of the eight studied species, biomass allocation to the leaves was favored; lipids were the first reserve exhausted before the first leaves were totally expanded in seven of the eight study species. Species with the highest N concentration had expanded leaves and lost their cotyledons faster than species with a low N concentration. Our results suggest that tropical deciduous forest species employ different strategies to survive the dry season and re-sprout in the next growing season mediated by seed reserve concentrations, translocation patterns and subsequent biomass allocation.

Prioritizing refugia for freshwater biodiversity conservation in highly seasonal ecosystems

AbstractAimRefugia play a key ecological role for the persistence of biodiversity in areas subject to natural or human disturbance. Temporary freshwater ecosystems regularly experience dry periods, which constrain the availability of suitable habitats. Current and future threats (e.g. water extraction and climate change) can exacerbate the negative effects of drying conditions. This could compromise the persistence of a large proportion of global freshwater biodiversity, so the identification and protection of refugia seems an urgent task.LocationNorthern Australia.MethodsWe demonstrate a new approach to identify and prioritize the selection of refugia and apply it to the conservation of freshwater fish biodiversity. We identified refugia using estimates of water residency time derived from satellite imagery and used a systematic approach to prioritize areas that provide all the fish species inhabiting the catchment with access to a minimum number of refugia while maximizing the length of stream potentially accessible for recolonization after the dry period. These priority refugia were locked into a broader systematic conservation plan with area‐based targets and direct connectivity. We accounted for current threats during the prioritization process to ensure degraded areas were avoided, thus maximizing the ecological role of priority refugia.ResultsPriority refugia were located in lowland reaches, where the incidence of threats was less prominent in our study area and headwaters in good condition. An additional set of 106 planning units (6500 km2) were required to represent 10% of each species' distribution in the broad conservation plan. A hierarchical management zoning scheme was applied to demonstrate how these key ecological features could be effectively protected from the major threats caused by aquatic invasive species and grazing.Main conclusionsThis new approach to identifying priority refugia and incorporating them into the conservation planning process in a systematic way would help enhance the resilience of freshwater biodiversity in temporary systems.

The onset of precipitation mediates plant–avian disperser interaction in recalcitrant seeds: the case of Cryptocarya alba (MOL) Looser, in Mediterranean ecosystems, Central Chile

Background: Arid and semi-arid environments impose limitations on plant regeneration. This is especially important during biotic dispersal in plants with recalcitrant seeds, in relation to when and where birds disperse these seeds. Aims: We examined the effect of the onset of seasonal precipitation on the regeneration of Cryptocarya alba (Lauraceae), comparing seedling recruitment during early and late onset of precipitations. Methods: We conducted field experiments using bird-dispersed and gravity-dispersed seeds; half of the seeds were placed during the initiation of precipitations; the other half was kept, then was placed in the forest ground 2 months later. We compared seedling recruitment probability among treatments. Results: Seedling recruitment was positively affected by avian dispersal. Seedling recruitment was significantly increased only for the fraction of bird-dispersed seeds that matched with the beginning of precipitations. Conclusions: The ecological context as well as seed recalcitrance are critical in determining the fate of bird-dispersed seeds. Although this trait may be not adaptive in seasonal ecosystems, it is correlated with other traits that are adaptive (seed size, directed dispersal, spread of the dispersal season), thus explaining the persistence of species with recalcitrant seeds in such environments.

Cumulative annual dung beetle diversity in Mediterranean seasonal environments

Species diversity assessments should consider the dynamic nature of ecological communities, especially in highly seasonal ecosystems. Here we provide a compre- hensive framework for analysing seasonal changes in species composition, richness and diversity in two local dung beetle (Coleoptera: Scarabaeoidea: Aphodiidae, Geotrupidae, and Scarabaeidae) communities from Wes- tern Tuscany (Italy), in the Mediterranean ecoregion. We test whether, in this highly seasonal region, cumulative annual diversity is an oversimplification of well differen- tiated seasonal communities. Data were obtained through repeated standardised samples collected regularly over an entire year. We clearly identify different summer and winter communities at each site based on species compo- sition and abundance. Seasonal richness and diversity values are different from the cumulative annual values, as a consequence of beta diversity between seasons, and some dung beetle species are identified as idiosyncratic of each particular season. Both ecological (niche partition- ing) and biogeographical factors are suggested as drivers of these temporal variations. Thus, because local inven- tories of fauna that include records over long time periods actually reflect situations where coexistence and interac- tions are unlikely to occur, highly seasonal sites must be viewed as having temporally differentiated communities in order to reach feasible and reliable baselines for local diversity assessments.