Oikos

Todd, Peter A.; Heery, Eliza C.; Loke, Lynette H. L.; Thurstan, Ruth H.; Kotze, D. Johan; Swan, Christopher

doi: 10.1111/oik.05946pmid: N/A

Human population density within 100 km of the sea is approximately three times higher than the global average. People in this zone are concentrated in coastal cities that are hubs for transport and trade – which transform the marine environment. Here, we review the impacts of three interacting drivers of marine urbanization (resource exploitation, pollution pathways and ocean sprawl) and discuss key characteristics that are symptomatic of urban marine ecosystems. Current evidence suggests these systems comprise spatially heterogeneous mosaics with respect to artificial structures, pollutants and community composition, while also undergoing biotic homogenization over time. Urban marine ecosystem dynamics are often influenced by several commonly observed patterns and processes, including the loss of foundation species, changes in biodiversity and productivity, and the establishment of ruderal species, synanthropes and novel assemblages. We discuss potential urban acclimatization and adaptation among marine taxa, interactive effects of climate change and marine urbanization, and ecological engineering strategies for enhancing urban marine ecosystems. By assimilating research findings across disparate disciplines, we aim to build the groundwork for urban marine ecology – a nascent field; we also discuss research challenges and future directions for this new field as it advances and matures. Ultimately, all sides of coastal city design: architecture, urban planning and civil and municipal engineering, will need to prioritize the marine environment if negative effects of urbanization are to be minimized. In particular, planning strategies that account for the interactive effects of urban drivers and accommodate complex system dynamics could enhance the ecological and human functions of future urban marine ecosystems.

Wang, Chao; Tang, Yujia

doi: 10.1111/oik.06099pmid: N/A

Phenology is one of the most sensitive processes of plant in response to global change. Anthropogenic activities have considerably increased nitrogen (N) deposition, which significant affects plant phenology. Although numerous individual studies have been conducted, it remains controversial how N addition affects phenological stages, and a comprehensive understanding of how plant phenology responds to external N inputs remains elusive. To reconcile the differences, we conducted a meta‐analysis of 117 species to examine the responses of plant phenology to N addition in terrestrial ecosystems, and assessed variations in their responses in relation to ecosystem types, functional groups, and environmental conditions. Our results showed that plant phenology changed significantly after N addition, and phenology time delayed and phenology duration shortened significantly across all biomes except fruiting duration, but varied with biome types. The phenology change in cropland was more dramatical than in grassland after N addition, even in opposite directions. The response of phenological stages to N addition was consistent in two pollination types except the flowering time, the flowering time had no change in anemophilous but significantly delayed in entomophilous. In addition, the response of phenology to N addition was discrepancy among functional groups, the phenology time advanced and duration shortened in sedge, while phenology time delayed and duration shortened in other groups, and the phenology change in legume was larger than grass and forbs. We also found that environmental factors had little effects on the response of plant phenology to N addition, but significant correlation was found between the response ratios of different phenological stages. Our study suggested that phenology was sensitive to N deposition at many phenological stages, and changes in phenology may be smaller with community biodiversity increasing at ecosystem level.

Xing, Xiaoke; Jacquemyn, Hans; Gai, Xuege; Gao, Yue; Liu, Qiang; Zhao, Zeyu; Guo, Shunxing

doi: 10.1111/oik.06363pmid: N/A

Understanding the processes that determine the architecture of interaction networks represents a major challenge in ecology and evolutionary biology. One of the most important interactions involving plants is the interaction between plants and mycorrhizal fungi. While there is a mounting body of research that has studied the architecture of plant–fungus interaction networks, less is known about the potential factors that drive network architecture. In this study, we described the architecture of the network of interactions between mycorrhizal fungi and 44 orchid species that represented different life forms and co‐occurred in tropical forest and assessed the relative importance of ecological, evolutionary and co‐evolutionary mechanisms determining network architecture. We found 87 different fungal operational taxonomic units (OTUs), most of which were members of the Tulasnellaceae. Most orchid species associated with multiple fungi simultaneously, indicating that extreme host selectivity was rare. However, an increasing specificity towards Tulasnellaceae fungal associates from terrestrial to epiphytic and lithophytic orchids was observed. The network of interactions showed an association pattern that was significantly modular (M = 0.7389, Mrandom = 0.6998) and nested (NODF = 5.53, p < 0.05). Terrestrial orchids had almost no links to modules containing epiphytic or lithophytic orchids, while modules containing epiphytic orchids also contained lithophytic orchids. Within each life form several modules were observed, suggesting that the processes that organize orchid–fungus interactions are independent of life form. The overall phylogenetic signal for both partners in the interaction network was very weak. Overall, these results indicate that tropical orchids associate with a wide number of mycorrhizal fungi and that ecological rather than phylogenetic constraints determine network architecture.

Cayuela, Hugo; Cruickshank, Sam S.; Brandt, Hannelore; Ozgul, Arpat; Schmidt, Benedikt R.

doi: 10.1111/oik.06286pmid: N/A

Life‐history theory states that, during the lifetime of an individual, resources are allocated to either somatic maintenance or reproduction. Resource allocation tradeoffs determine the evolution and ecology of life‐history strategies and determine an organisms’ position along the fast–slow continuum. Theory predicts that environmental stochasticity is an important driver of resource allocation and therefore life‐history evolution. Highly stochastic environments are expected to increase uncertainty in reproductive success and select for iteroparity and a slowing down of the life history. To date, most empirical studies have used comparisons among species to examine these theoretical predictions. By contrast, few have investigated how environmental stochasticity affects life‐history strategies at the intraspecific level. In this study, we examined how variation in breeding site stochasticity (among‐year variability in pond volume and hydroperiod) promotes the co‐occurrence of different life‐history strategies in a spatially structured population, and determines life‐history position along the fast–slow continuum in the yellow‐bellied toad Bombina variegata. We collected mark–recapture data from a metapopulation and used multievent capture–recapture models to estimate survival, recruitment and breeding probabilities. We found higher survival and longer lifespans in populations inhabiting variable sites compared to those breeding in stable ones. In addition, probabilities of recruitment and skipping a breeding event were higher in variable sites. The temporal variance of survival and recruitment probabilities, as well as the probability to skip breeding, was higher in variable sites. Taken together, these findings indicate that populations breeding in variable sites experienced a slowing down of the life‐history. Our study thus revealed similarities in the macroevolutionary and microevolutionary processes shaping life‐history evolution.

Perry, George L. W.; Lee, Finnbar

doi: 10.1111/oik.06052pmid: N/A

Metapopulation persistence depends on connectivity between habitat patches. While emphasis has been placed on the spatial dynamics of connectivity, much less has been placed on its short‐term temporal dynamics. In many terrestrial and aquatic ecosystems, however, transient (short‐term) changes in connectivity occur as habitat patches are connected and disconnected due, for example, to climatic or hydrological variability. We evaluated the implications of transient connectivity using a network‐based metapopulation model and a series of scenarios representing temporal changes in connectivity. The transient loss of connectivity can influence metapopulation persistence, and more strongly autocorrelated temporal dynamics affect metapopulation persistence more severely. Given that many ecosystems experience short‐term and temporary loss of habitat connectivity, it is important that these dynamics are adequately represented in metapopulation models; failing to do so may yield overly optimistic‐estimates of metapopulation persistence in fragmented landscapes.

Simmons, Benno I.; Vizentin‐Bugoni, Jeferson; Maruyama, Pietro K.; Cotton, Peter A.; Marín‐Gómez, Oscar H.; Lara, Carlos; Rosero‐Lasprilla, Liliana; Maglianesi, María A.; Ortiz‐Pulido, Raul; Rocca, Márcia A.; Rodrigues, Licléia C.; Tinoco, Boris A.; Vasconcelos, Marcelo F.;

Xiao, Sa; Atwater, Daniel Z.; Callaway, Ragan M.

doi: 10.1111/oik.05915pmid: N/A

Plant–soil feedbacks have important effects on plant communities, but most theory has been derived from experiments on intraspecific plant–soil feedbacks. Much less is known about how interspecific plant–soil feedbacks affect coexistence and plant communities, due in part to experimental and analytical challenges. Here, we propose a framework for evaluating plant–soil feedbacks among multiple interacting species that incorporates 1) the average effect each species has on conspecific and heterospecific neighbors via how they modify soil biota, 2) the average response of each species to the soil modifications made by neighboring species, and 3) intraspecific feedback. We refer to this as the ‘effect–response–intraspecific’ (ERI) model. We used individual‐based models to evaluate the relative importance of intraspecific and interspecific soil feedback in determining species abundance ranks in simulated plant communities. To compare the heuristic value of the ERI model to that of an established model in which effects and responses to soil feedback are not explicitly recognized, we evaluated a ‘full‐factorial’ model in which soil feedbacks among five plant species were measured and then explicitly modeled. The ERI model indicated that the response to interspecific plant–soil feedbacks was the key factor for species’ abundance rank without spatial structure. In contrast, interspecific plant–soil feedback had no impact on species abundance with spatial structure, and intraspecific feedback became dominant. Thus, our models predict that the relative importance of intraspecific and interspecific feedbacks changes as a function of the degree of spatial structure in a system. Overall, the ERI model provides a novel and tractable framework for evaluating complex multi‐species plant–soil feedbacks.

Fouzai, Nadia; Opdal, Anders F.; Jørgensen, Christian; Fiksen, Øyvind

doi: 10.1111/oik.05631pmid: N/A

Prey modify their behaviour to avoid predation, but dilemmas arise when predators vary in hunting style. Behaviours that successfully evade one predator sometimes facilitate exposure to another predator, forcing the prey to choose the lesser of two evils. In such cases, we need to quantify behavioural strategies in a mix of predators. We model optimal behaviour of Atlantic cod Gadus morhua larvae in a water column, and find the minimal vulnerability from three common predator groups with different hunting modes; 1) ambush predators that sit‐and‐wait for approaching fish larvae; 2) cruising invertebrates that eat larvae in their path; and 3) fish which are visually hunting predators. We use a state‐dependent model to find optimal behaviours (vertical position and swimming speed over a diel light cycle) under any given exposure to the three distinct modes of predation. We then vary abundance of each predator and quantify direct and indirect effects of predation. The nature and strength of direct and indirect effects varied with predator type and abundance. Larvae escaped about half the mortality from fish by swimming deeper to avoid light, but their activity level and cumulative predation from ambush predators increased. When ambush invertebrates dominated, it was optimal to be less active but in more lit habitats, and predation from fish increased. Against cruising predators, there was no remedy. In all cases, the shift in behaviour allowed growth to remain almost the same, while total predation were cut by one third. In early life stages with high and size‐dependent mortality rates, growth rate can be a poor measure of the importance of behavioural strategies.

Simon, Ricardo Nouailhetas; Cherry, Seth G.; Fortin, Daniel

doi: 10.1111/oik.06166pmid: N/A

The spatiotemporal game between predators and prey is a fundamental process governing their distribution dynamics. Players may adopt different tactics as the associated costs and benefits change through time. Yet few studies have investigated the potentially simultaneous and dynamic nature of movement tactics used by both players. It is particularly unclear to what extent perceived predation risk mediates the fine‐scale distribution of large and dangerous prey, which are mostly driven by bottom–up, resource‐related processes. We built habitat use and movement models based on 10 years of monitoring GPS‐collared grey wolves Canis lupus and plains bison Bison bison bison in Prince Albert National Park, Canada, to investigate the predator–large prey game in a multi‐prey system. Bison did not underuse patches of high‐quality vegetation at any time during the seasonal cycle even though wolves were selectively patrolling these areas. Rather, in at least one season, bison engaged in complex tactics comprised of proactive responses to the long‐term distribution (risky places) and reactive responses to the immediate proximity (risky times) of their opponent. In summer–autumn, bison reduced the time spent in food‐rich patches as both the long‐term use and the immediate proximity of wolves increased. By demonstrating that wolf distribution triggers patch abandonment by bison, we provide a key element in support of the shell game hypothesis – where prey move constantly to avoid predators attempting to anticipate their location. In winter, a season of relatively high energetic stress, bison no longer abandoned food‐rich patches as predation risk increased, while no bison responses to wolves were observed in spring–summer. Our work demonstrates the highly dynamic and complex nature of the predator–large prey spatiotemporal game, a key trait‐mediated mechanism by which trophic interactions structure ecological communities.

Thieltges, David W.; Goedknegt, M. Anouk; O'Dwyer, Katie; Senior, Alistair M.; Kamiya, Tsukushi

doi: 10.1111/oik.06086pmid: N/A

Stable isotopes are widely used to identify trophic interactions and to determine trophic positions of organisms in food webs. Comparative studies have provided general insights into the variation in isotopic composition between consumers and their diet (discrimination factors) in predator–prey and herbivore–plant relationships while other major components of food webs such as host–parasite interactions have been largely overlooked. In this study, we conducted a literature‐based comparative analysis using phylogenetically‐controlled mixed effects models, accounting for both parasite and host phylogenies, to investigate patterns and potential drivers in Δ13C and Δ15N discrimination factors in metazoan parasitic trophic interactions. Our analysis of 101 parasite–host pairs revealed a large range in Δ13C (–8.2 to 6.5) and Δ15N (–6.7 to 9.0) among parasite species, with no significant overall depletion or enrichment of 13C and 15N in parasites. As previously found in other trophic interactions, we identified a scaling relationship between the host isotopic value and both discrimination factors with Δ13C and Δ15N decreasing with increasing host δ13C and δ15N, respectively. Furthermore, parasite phylogenetic history explained a large fraction (>60%) of the observed variation in the Δ15N discrimination factor. Our findings suggest that the traditional isotope ecology framework (using an average Δ15N of 3.4‰) applies poorly to parasitic trophic interactions. They further indicate the need for a scaled rather than a fixed trophic discrimination factor framework along gradients of host δ15N. We also identified several conceptual and methodological issues which should to be considered in future research to help integrate parasitic interactions into a holistic isotope ecology framework across diverse trophic interactions.