The evolution of species interactions across natural landscapes

Given the potential for rapid and microgeographical adaptation, ecologists increasingly are exploring evolutionary explanations for community patterns. Biotic selection can generate local adaptations that alter species interactions. Although some gene flow might be necessary to fuel local adaptation, higher gene flow can homogenise traits across regions and generate local maladaptation. Herein, I estimate the contributions of local biotic selection, gene flow and spatially autocorrelated biotic selection to among-population divergence in traits involved in species interactions across 75 studies. Local biotic selection explained 6.9% of inter-population trait divergence, an indirect estimate of restricted gene flow explained 0.1%, and spatially autocorrelated selection explained 9.3%. Together, biotic selection explained 16% of the variance in population trait means. Most biotic selection regimes were spatially autocorrelated. Hence, most populations receive gene flow from populations facing similar selection, which could allow for local adaptation despite moderate gene flow. Gene flow constrained adaptation in studies conducted at finer spatial scales as expected, but this effect was often confounded with spatially autocorrelated selection. Results indicate that traits involved in species interactions might often evolve across landscapes, especially when biotic selection is spatially autocorrelated. The frequent evolution of species interactions suggests that evolutionary processes might often influence community ecology.     

Do Species Sorting and Mass Effects Drive Assembly in Tropical Agroecological Landscape Mosaics?

Recent assessments of biodiversity in tropical agroecosystems have revealed surprisingly high functional and taxonomic diversity in systems with low management intensity. This biodiversity is the product of community assembly. Because agroecosystems are novel ecosystems and occur in landscape mosaics, the assembly processes generating communities in agroecosystems are poorly resolved. Broadly, two models have been proposed to explain landscape assembly: trade‐offs in species performance across habitats (species sorting) and source‐sink dynamics between habitats of differential quality (mass effects). These models are largely untested in tropical agroecosystems. We utilize an extensive data set on a tropical twig‐nesting ant community from five microhabitat types in a shaded coffee agroecosystem to test for species sorting, mass effects, or a mixed model. To test among these models, we used community similarity and a variance decomposition on a focal microhabitat (a moderate‐shade coffee farm) to partition community variance into spatial and environmental components. To identify the source habitat for mass effects and assess their strength, we measured dispersing alates (winged reproductives), artificial nests, and colony and nest size in shade trees and coffee. We found significant environmental and spatial signal and evidence for both species sorting and mass effects. We find sorting occurs among common species, but that mass effects are prevalent among rare species and likely originate in the shade trees. Our results indicate that both metacommunity models occur in tropical landscape mosaics, but they may not apply equally to all species in communities, habitat gradients, or timescales.     

Fungal infection alters the selection,dispersal and drift processes structuring the amphibian skin microbiome

Symbiotic microbial communities are important for host health, but the processes shaping these communities are poorly understood. Understanding how community assembly processes jointly affect microbial community composition is limited because inflexible community models rely on rejecting dispersal and drift before considering selection. We developed a flexible community assembly model based on neutral theory to ask: How do dispersal, drift and selection concurrently affect the microbiome across environmental gradients? We applied this approach to examine how a fungal pathogen affected the assembly processes structuring the amphibian skin microbiome. We found that the rejection of neutrality for the amphibian microbiome across a fungal gradient was not strictly due to selection processes, but was also a result of species‐specific changes in dispersal and drift. Our modelling framework brings the qualitative recognition that niche and neutral processes jointly structure microbiomes into quantitative focus, allowing for improved predictions of microbial community turnover across environmental gradients.     

Effects of nonnative species on the stability of riverine fish communities

Despite the increasing ubiquity of biological invasions worldwide, little is known about the scale-dependent effects of nonnative species on real-world ecological dynamics. Here, using an extensive time series dataset of riverine fish communities across different biogeographic regions of the world, we assessed the effects of nonnative species on the temporal variability and synchrony in abundance at different organizational levels (population, metapopulation, community and metacommunity) and spatial scales (stream reach and river basin). At the reach scale, we found that populations of nonnative species were more variable over time than native species, and that this effect scaled up to the community level – significantly destabilizing the dynamics of riverine fish communities. Nonnative species not only contributed to reduced community stability, but also increased variability of native populations. By contrast, we found no effect of nonnative species dominance on local interspecific synchrony among native species. At the basin scale, nonnative metapopulations were again more variable than the native ones. However, neither native metapopulations nor metacommunities showed differences in temporal variability or synchrony as nonnative species dominance increased basin-wide. This suggests a ‘dilution effect’ where the contribution to regional stability of local native populations from sites displaying low levels of invasion reduced the destabilizing effects of nonnative species. Overall, our results indicate that accounting for the destabilizing effect of nonnative species is critical to understanding native species persistence and community stability.     

Metacommunity theory for transmission of heritable symbionts within insect communities

Microbial organisms are ubiquitous in nature and often form communities closely associated with their host, referred to as the microbiome. The microbiome has strong influence on species interactions, but microbiome studies rarely take interactions between hosts into account, and network interaction studies rarely consider microbiomes. Here, we propose to use metacommunity theory as a framework to unify research on microbiomes and host communities by considering host insects and their microbes as discretely defined “communities of communities” linked by dispersal (transmission) through biotic interactions. We provide an overview of the effects of heritable symbiotic bacteria on their insect hosts and how those effects subsequently influence host interactions, thereby altering the host community. We suggest multiple scenarios for integrating the microbiome into metacommunity ecology and demonstrate ways in which to employ and parameterize models of symbiont transmission to quantitatively assess metacommunity processes in host‐associated microbial systems. Successfully incorporating microbiota into community‐level studies is a crucial step for understanding the importance of the microbiome to host species and their interactions.     

Dispersal limitation of unionid mussels and implications for their conservation

1. Freshwater unionid mussels are a highly imperilled group. Their dispersal abilities depend on the availability and the movement of host fish on which their parasitic mussel larvae develop. 2. We examined the relationship between the dispersal abilities of unionid mussels and their conservation status on a regional (SW Ontario) scale and their distribution and abundance on a catchment scale (Sydenham River, SW Ontario) by determining host specificity and estimating the dispersal abilities of mussels on fish from a review of the literature. 3. On the regional scale, we found that mussels with the most precarious conservation status relied on host fish with short movement distances, whereas vulnerable and more secure mussel species had host fish with 2–3 orders of magnitude larger movement distances. We were not able to detect a clear pattern on the catchment scale. 4. Our results suggest that limited dispersal by host fish affects the abundance and distribution of unionid mussels and ultimately their conservation status on a regional scale. Information on dispersal limitations because of differences in host fish communities should be included in conservation and management decisions to ensure connectivity and maintain functioning mussel metacommunities.     

栖息地永久性破坏的比例对物种多度稳定值影响的迭代算法

为了分析栖息地破坏程度对集合群落中物种多度稳定值的影响,基于Tilman等[1, 2]提出的多物种竞争的集合群落模型,设计了一种通用的迭代算法用以分析栖息地永久性破坏的比例对物种多度稳定值的影响。针对Tilman等[2]提出的物种多度与其扩散能力或者与其竞争能力相互关系的四种模型,也即：（1）物种竞争力越强则其多度稳定值越大,所有物种死亡率相同;（2）所有物种不论竞争力如何,其多度稳定值相同、死亡率也相同;（3）物种竞争力越弱则其多度稳定值越大,所有物种死亡率相同;（4）物种多度的稳定值相同,但物种竞争力越弱其死亡率越高。先前的研究已经阐明了在前2种模型中栖息地永久性破坏的比例对物种多度稳定值的影响;而对于模型3,因为其数学表达式较为复杂,先前的研究者不得不使用模型3的简化式来考察栖息地永久性破坏的比例对物种多度稳定值的影响;而对于模型4,由于其数学表达式更为复杂,栖息地永久性破坏的比例对物种多度稳定值的影响未能被以往的研究所阐明。本文所使用的迭代算法可以阐明四种模型中任何一种模型条件下栖息地永久性破坏的比例对物种多度稳定值的影响。我们发现对于模型1和2迭代算法所得到的物种多度稳定值与通过数学解析式分析的结果完全一致,同时通过使用迭代算法还阐明了模型4中栖息地永久性破坏的比例对物种多度稳定值的影响。假设栖息地永久性破坏的比例达到了能够导致第s个物种灭绝的水平,起初幸存物种竞争力的排序为s 1 ~ s 3 ~ s 5 ~ … ~ s 6 ~ s 4 ~ s 2,但是随着栖息地永久性破坏的比例不断增大,当其快达到（但还未达到）能够导致第s 1个物种灭绝的水平,物种竞争力的排序将变为s 2 ~ s 4 ~ s 6 ~ … ~ s 5 ~ s 3 ~ s 1。模型4中栖息地永久性破坏的比例对物种多度稳定值的影响与模型2中栖息地永久性破坏程度对物种多度稳定值的影响几乎一致,唯一不同是模型2中所有物种栖息地稳定值的曲线有一个共同的交点,而模型4中所有物种栖息地稳定值的曲线交点不唯一。此外,还使用迭代算法考对比了模型3原始数学表达式和简化式两种情况下栖息地永久性破坏的比例对物种多度稳定值的影响,发现结果略有不同。     

Diversity patterns in upper Cambrian to Lower Ordovician trilobite communities of north‐western Argentina

The hierarchical structure of biodiversity from a regional scale analysis has received much attention as an alternative approach to unravelling the principal drivers of biodiversification. To better understand the processes that control the diversification of Cambro‐Ordovician trilobite communities from the Argentine Cordillera Oriental, we explore patterns of occupancy and diversity trajectories at the local and regional scales through seven intervals (Furongian, loTr1, upTr1, loTr2, upTr2, Tr3 and Fl2–3), and across an onshore‐offshore profile. Our results indicate: (1) a decrease in regional diversity from the upper Tr2 onwards, mainly caused by a reduction in the number of rare taxa, coupled with stable beta diversity at regional scale and a constant rise in beta diversity in deep subtidal environments; (2) a higher proportion of regional diversity allocated to the within‐habitat beta component; and (3) that changes in gamma diversity are driven primarily by changes in alpha diversity during the Furongian–Tr3, whereas in the Floian, beta diversity seems to modulate regional diversity. These trends and associated patterns indicate increasing ecological differences among taxa, shifting from metacommunities where most taxa have similar ecological preferences or ‘Hubbell type’ to metacommunities with high niche differentiation or ‘Hutchinson type’. Interestingly, the timing of this shift coincides with the regional‐scale turnover between trilobite evolutionary faunas suggesting that the rise in niche differentiation among these genera may be related to the transition. Superimposed on this general trend, particular diversity structures can be understood in the light of metacommunity dynamics, such as dispersal limitation and mass effect.     

The challenges that spatial context present for synthesizing community ecology across scales

Accurately characterizing spatial patterns on landscapes is necessary to understand the processes that generate biodiversity, a problem that has applications in ecological theory, conservation planning, ecosystem restoration, and ecosystem management. However, the measurement of biodiversity patterns and the ecological and evolutionary processes that underlie those patterns is highly dependent on the study unit size, boundary placement, and number of observations. These issues, together known as the modifiable areal unit problem, are well known in geography. These factors limit the degree to which results from different metacommunity and macro‐ecological studies can be compared to draw new inferences, and yet these types of comparisons are widespread in community ecology. Using aquatic community datasets, we demonstrate that spatial context drives analytical results when landscapes are sub‐divided. Next, we present a framework for using resampling and neighborhood smoothing to standardize datasets to allow for inferential comparisons. We then provide examples for how addressing these issues enhances our ability to understand the processes shaping ecological communities at landscape scales and allows for informative meta‐analytical synthesis. We conclude by calling for greater recognition of issues derived from the modifiable areal unit problem in community ecology, discuss implications of the problem for interpreting the existing literature, and identify tools and approaches for future research.     

Flood pulse regulation of bacterioplankton community composition in an Amazonian floodplain lake

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