Loss Of Species Richness Research Articles

Linking changes of forage production and digestibility with grassland community assembly under nitrogen enrichment

BackgroundForage production is the fundamental ecosystem service of grasslands. Although forage consumption occurs at community level, most studies focused on species-level changes of forage quality. The quantitative and qualitative changes of forage production are driven by species-specific trait, intra-specific plasticity, and species turnover. We examined the changes in forage production and digestibility after 5-year factorial treatments of nitrogen (N) addition and mowing in a temperate steppe and linked such changes to community assembly under the Price equation framework.ResultsNitrogen addition significantly reduced species richness, increased forage production, but did not change forage digestibility (indicated by the total Ca+Mg concentrations). Mowing did not affect forage production and digestibility. The positive effects of N addition on forage production were driven by the enhancement of abundance of the remaining species following N enrichment, rather than by species loss or species gain. The species identity effects could offset the effects of species richness loss or gain on forage production and digestibility.ConclusionsOur results highlight the importance of a community perspective in addressing the quantitative and qualitative changes of forage production under global change pressure of N enrichment. Species identity is important in determining the contribution of different processes of community assembly to ecosystem services.

Vulnerability of bat-plant pollination interactions due to environmental change.

Plant-pollinator interactions are highly relevant to society as many crops important for humans are animal pollinated. However, changes in climate and land use may put such interacting patterns at risk by disrupting the occurrences between pollinators and the plants they pollinate. Here, we analyse how the co-occurrence patterns between bat pollinators and 126 plant species they pollinate may be disrupted given changes in climate and land use, and we forecast relevant changes of the current bat-plant co-occurrence distribution patterns for the near future. We predict under RCP8.5 21% of the territory will experience a loss of bat species richness, plants with C3 metabolism are predicted to reduce their area of distribution by 6.5%, CAM species are predicted to increase their potential area of distribution up to 1% and phanerophytes are predicted to have a 14% reduction in their distribution. The potential bat-plant interactions are predicted to decrease from an average of 47.1 co-occurring bat-plant pairs in the present to 34.1 in the pessimistic scenario. The overall changes in suitable environmental conditions for bats and the plant species they pollinate may disrupt the current bat-plant co-occurrence network and will likely put at risk the pollination services bat species provide.

Latitudinal variation in the diversity–disturbance relationship demonstrates the context dependence of disturbance impacts

AbstractAimThe shape of the diversity–disturbance relationship is context dependent, but the mechanisms driving this context dependence are unclear due to limited standardized empirical assessments across different environmental and ecological settings. At seven sites and over 20° of latitude, spanning both temperate and tropical systems, we measured community response to a fine‐scale experimental disturbance gradient in communities of benthic invertebrates.LocationEast coast of Australia (16.48–36.43° S).Time periodSixty‐six weeks (August 2012–November 2013).Major taxa studiedBenthic marine invertebrates.MethodsCommunities were grown on acrylic tiles and subjected to four experimental disturbance events over a 66‐week period. At the end of this period, the effect of increasing disturbance extent (from 0% to 100% community clearance) on measures of alpha and beta diversity were assessed.ResultsIn the tropics, richness and diversity increased with disturbance because the creation of free space allowed for the colonization of new recruits. In temperate communities, increasing disturbance led to a monotonic loss in species richness and a more hump‐shaped relationship in evenness and diversity. In the tropics, compositional change with increasing disturbance was driven by changes in species identities and abundances as the cover of rare species increased. In temperate regions, however, differences in species abundances were primarily responsible for compositional changes, reflecting the shift to algal dominance in conditions of high disturbance.Main conclusionsThe shape of the diversity–disturbance relationship changed over latitude, indicating that the concept of “intermediate” disturbance differs amongst these communities. Faster rates of increases in bare space, loss of species richness and a shift to algal dominance suggest that, in these systems, higher‐latitude communities are more susceptible to negative outcomes of high levels of disturbance than lower‐latitude communities. We discuss how differences in community dynamics, including competition, regional diversity and availability of propagules, help to explain this pattern.

Bird species assemblages differ, while functional richness is maintained across an urban landscape

Urbanization poses serious threats to biodiversity in many regions of the developing world. Understanding the factors that influence bird communities at the local and landscape level is important to guide urban planning efforts toward enhancing bird diversity. How bird species richness and diversity vary and the environmental factors that optimize their functional diversity in urban settlements remains poorly understood. We investigated the relationship between environmental characteristics and bird taxonomic and functional diversity across an urban settlement density gradient in Harare, Zimbabwe. Seventy-two transects were surveyed for bird species and environmental characteristics, and 6639 birds representing 94 species were recorded. Bird species richness and diversity declined from low to high settlement density sites, whereas bird functional diversity and abundance did not vary across the urban settlement density gradient. Characteristic species for low and high settlement density sites were Purple-crested Turaco (Tauraco porphyreolophus) and Pearl-breasted Swallow (Hirundo dimidiata), respectively. There were significant dissimilarities in bird species assemblages across the urban gradient. We demonstrated that the presence of water features and vegetation (presence of flowering plants and tree height) were the most significant environmental predictors of bird functional diversity. Loss in species richness across the urban settlement density gradient does not seem to be accompanied by significant declines in functional richness. The key message for urban planning here is that; despite the homogenization of urban environments and loss of bird species richness (Melles et al., 2003), broad ecosystem functionality may be maintained across the urban settlement density gradient.

Response of the Zygopteran Community (Odonata: Insecta) to Change in Environmental Integrity Driven by Urbanization in Eastern Amazonian Streams

The accelerated and disordered growth of large urban centers has caused a significant loss of biodiversity and the negative effects are more significant in aquatic environments. Thus, the objective of this study is to assess the effects of environmental change due to urbanization in the abundance and biomass patterns of species belonging to the Zygoptera suborder. We tested the hypothesis that, in altered streams, there will be a predominance of organisms with fast growth and small biomass (r-strategists), and intermediate streams will have an overlapping of r and k-strategists. In control streams, there will be a predominance of k-strategists, with slow growth, decreased abundance, and high biomass. Urban expansion in Amazonian streams will cause loss of Zygoptera species richness. Streams draining urban areas will have higher air temperatures than control streams. Thus, small-sized and less abundant species will be favored. We sampled 15 streams in the metropolitan area of Belém. Sites were classified, using the index of physical habitat integrity, as control, intermediate and altered. Comparisons between biomass and abundance were analyzed using W Statistics. Our analyses showed that: the effects of urbanization cause loss of k-strategists and favors r-strategists, once abundance was placed above biomass; in intermediate environments, contrary to what we expected, there was no overlapping of strategies, once r-strategists were also placed above k-strategists; in control environments, biomass was placed above abundance, suggesting these environments have a predominance of k-strategist species, as we suggested; and we observed increased levels of temperature favor the most abundant species, the ones having generalist biological mechanisms; however, contrary to what we expected, there was no difference in richness. With these results, we reinforce the need for public policies to create or maintain the riparian forest along streams running through urban areas and create or maintain urban parks.

Lost and found: 160 years of Lepidoptera observations in Wuppertal (Germany)

In the light of the current discussion on reduced insect biomass and species decline, we would like to draw attention to the work of amateur entomologists who have been observing the moth and butterfly fauna for decades. Actually, the recording of butterflies and moths has a long tradition in Wuppertal and its surroundings (Germany, North Rhine-Westfalia, Bergisches Land). Therefore, we have access to rather detailed data of the local macrolepidoptera fauna collected over the last 160 years and are able to comment on the trends of moth and butterfly populations during this rather long period. We review historical and current data and provide a comprehensive abundance list of all macrolepidoptera species observed in the study region. We found that, from the mid-twentieth century onwards, the species richness of butterfly and moths species decreased considerably. In terms of the number of species evaluated (537), we see that 27% decreased within the last 160 years while 15% have already been lost. Additionally, 24% are apparently stable at a low level. Particularly affected are highly specialised species of heath, moor, grassland, scrub, coppice and orchard habitats. However, 15% of the evaluated species are observed more frequently. Some of these newly colonised the study region (2.4%). Since Wuppertal is a city that profited from the industrial revolution from the middle of the nineteenth century onwards, we think that our results could serve as a representative example of the loss of species richness due to industrialisation, urbanisation, intensive agriculture and forestry. If we intend to increase species richness of butterflies and moths again, the focus must be on protecting, restoring and promoting low-nutrient open landscape habitats rather than forests.

Risk of short-term biodiversity loss under more persistent precipitation regimes.

Recent findings indicate that atmospheric warming increases the persistence of weather patterns in the mid-latitudes, resulting in sequences of longer dry and wet periods compared to historic averages. The alternation of progressively longer dry and wet extremes could increasingly select for species with a broad environmental tolerance. As a consequence, biodiversity may decline. Here we explore the relationship between the persistence of summer precipitation regimes and plant diversity by subjecting experimental grassland mesocosms to a gradient of dry-wet alternation frequencies whilst keeping the total precipitation constant. The gradient varied the duration of consecutive wet and dry periods, from 1 up to 60days with or without precipitation, over a total of 120days. An alternation of longer dry and wet spells led to a severe loss of species richness (up to -75% relative to the current rainfall pattern in W-Europe) and functional diversity (enhanced dominance of grasses relative to nitrogen (N)-fixers and non-N-fixing forbs). Loss of N-fixers and non-N-fixing forbs in severe treatments was linked to lower baseline competitive success and higher physiological sensitivity to changes in soil moisture compared to grasses. The extent of diversity losses also strongly depended on the timing of the dry and wet periods. Regimes in which long droughts (≥20days) coincided with above-average temperatures showed significantly more physiological plant stress over the experimental period, greater plant mortality, and impoverished communities by the end of the season. Across all regimes, the duration of the longest period below permanent wilting point was an accurate predictor of mortality across the communities, indicating that increasingly persistent precipitation regimes may reduce opportunities for drought stress alleviation. We conclude that without recruitment, which was precluded in this experiment, summer precipitation regimes with longer dry and wet spells will likely diminish plant diversity, at least in the short term.

Mowing does not redress the negative effect of nutrient addition on alpha and beta diversity in a temperate grassland

Abstract Species loss due to an increasing the number of added nutrients has been explained by both light competition through biomass increase and by niche dimension reduction as a result of species‐specific limiting soil resources trade‐offs. Disturbances, by reducing community biomass, species dominance and increasing light availability, may counteract above‐ground nutrient effects. However, it is unknown if diversity loss at local or spatial scales generated by increasing the number of added nutrients can be redressed with canopy disturbance. We evaluated if local (alpha) and spatial scale (beta) diversity loss generated by the number of added nutrients can be reverted by disturbances in Flooding Pampa grasslands, Argentina. In a 4‐year replicated field experiment, we added soil resources combining nitrogen, phosphorus and potassium to obtain 0, 1, 2 or 3 nutrients and manipulated the regime of canopy disturbance by seasonal mowing and biomass removal. We found that the increasing the number of added nutrients strongly reduced local and spatial plant diversity, despite biomass and light changes generated by mowing. In mown plots, nutrient‐driven local diversity loss intensified along time, thus increasing species dominance. While mowing did not affect dominant species loss, increasing the number of added nutrients promoted rare species loss and reduced spatial dissimilarity. Furthermore, mowing increased local and spatial diversity regardless of light or biomass effects, suggesting alternative pathway effects for disturbance. Synthesis. Our results demonstrate that even when disturbance generated a positive effect on local and spatial diversity, it did not completely counteract the negative effect of number of added nutrients. Thus, the relative importance of above‐ and below‐ground resource competition may change when chronic disturbances alter community dominance. Under low light availability, above‐ground competition may drive species richness loss but when disturbance reduces light limitation, the increasing the number of added nutrients may reduce niche dimensionality and thus species coexistence. In sum, faced with the need to manage eutrophized grasslands, our study showed that disturbance may not completely mitigate the negative effect of multiple nutrient inputs on local and spatial grassland diversity.

An interactive identification key for Atlantic Forest tree species based on macroscopic wood anatomy

Abstract The Atlantic Forest is considered a biodiversity hotspot because of its exceptional species richness, endemism, and habitat losses. Commercial logging, industrial forestry, and agriculture represent threats to the Atlantic Forest, and even though it has been protected by law since 2006, forest suppression continues and large volumes of Atlantic Forest wood are traded every year. To promote environmental conservation and prevent illegal logging, the verification of wood species’ identifications is fundamental throughout several stages of the wood supply chain by supervisory bodies, traders, and even consumers. Macroscopic wood anatomy analysis has been shown to be an efficient method for screening, although tools to streamline the efficiency of that process are necessary. We introduce here an interactive identification key for Atlantic Forest tree species, based on standard wood macroscopic features that is now available online at http://gbg.sites.uff.br/lamad/.

The erosion of biodiversity and biomass in the Atlantic Forest biodiversity hotspot

Tropical forests are being deforested worldwide, and the remaining fragments are suffering from biomass and biodiversity erosion. Quantifying this erosion is challenging because ground data on tropical biodiversity and biomass are often sparse. Here, we use an unprecedented dataset of 1819 field surveys covering the entire Atlantic Forest biodiversity hotspot. We show that 83−85% of the surveys presented losses in forest biomass and tree species richness, functional traits, and conservation value. On average, forest fragments have 25−32% less biomass, 23−31% fewer species, and 33, 36, and 42% fewer individuals of late-successional, large-seeded, and endemic species, respectively. Biodiversity and biomass erosion are lower inside strictly protected conservation units, particularly in large ones. We estimate that biomass erosion across the Atlantic Forest remnants is equivalent to the loss of 55−70 thousand km2 of forests or US$2.3−2.6 billion in carbon credits. These figures have direct implications on mechanisms of climate change mitigation.

Fragment size and the disassembling of local bird communities in the Atlantic Forest: A taxonomic and functional approach

Habitat loss is the primary driver of the decline of biodiversity in ecological communities. However, which ecological processes are implicated in the removal of species following habitat loss, i.e. the disassembling of the community, remains unclear in many ecosystems. We address this question by investigating how the taxonomic and functional diversity of bird assemblages are related to fragment size in the Atlantic Forest from northeastern Brazil. We used complementary metrics of diversity and a randomization procedure to test whether changes in diversity result from either random or deterministic processes, such as limiting similarity or habitat filtering. The species–area (SAR) and functional richness–area (FAR) relationships were positive, as expected. However, the FAR had a lower slope than the SAR, which indicates a slower loss of functional richness than that predicted by the loss of species richness. Communities in smaller fragments contain more functionally overdispersed species and a more even distribution of abundance. These results indicate that limiting similarity drives the disassembling of bird assemblages in small fragments of the Atlantic Forest, which presumably reflects increased competition. This dynamic tends to reduce functional redundancy in the impoverished assemblages, with potentially deleterious consequences for ecosystem functioning and forest conservation.

Diversity-dependent soil acidification under nitrogen enrichment constrains biomass productivity.

In most plant communities, the net effect of nitrogen enrichment is an increase in plant productivity. However, nitrogen enrichment also has been shown to decrease species richness and to acidify soils, each of which may diminish the long-term impact of nutrient enrichment on productivity. Here we use a long-term (20year) grassland plant diversity by nitrogen enrichment experiment in Minnesota, United States (a subexperiment within the BioCON experiment) to quantify the net impacts of nitrogen enrichment on productivity, including its potential indirect effects on productivity via changes in species richness and soil pH over an experimental diversity gradient. Overall, we found that nitrogen enrichment led to an immediate positive increment in productivity, but that this effect became nonsignificant over later years of the experiment, with the difference in productivity between fertilized and unfertilized plots decreasing in proportion to nitrogen addition-dependent declines in soil pH and losses of plant diversity. The net effect of nitrogen enrichment on productivity could have been 14.5% more on average over 20years in monocultures if not for nitrogen-induced decreases in pH and about 28.5% more on average over 20years in 16 species communities if not for nitrogen-induced species richness losses. Together, these results suggest that the positive effects of nutrient enrichment on biomass production can diminish in their magnitude over time, especially because of soil acidification in low diversity communities and especially because of plant diversity loss in initially high diversity communities.

Balancing biodiversity and agriculture: Conservation scenarios for the Dutch dairy sector

Biodiversity is declining and current strategies to halt biodiversity loss have not succeeded. In preparing the EU’s Biodiversity Strategy 2030, it is essential to unravel different visions about conservation targets for agriculture, and to understand potential trade-offs with food production. In this research, we translated the narratives of experts into two conservation scenarios on a case study area resembling the Dutch dairy sector. The scenarios reflected a targeted versus a generic approach towards conservation. In the targeted conservation (TC) scenario, extensive grassland, reduced drainage and delayed mowing were applied in core areas to enhance meadow bird abundance, whereas in the generic conservation (GC) scenario, networks of nature and extensive agriculture were created and no feed was imported, which required a change in local agricultural land use. Subsequently, total feed and food (milk and meat) production and potential impacts on biodiversity were assessed, using the total energy and protein value for dairy, dairy productivity and the potentially disappeared fraction (PDF) of plant species richness. Land use changed on 6% of the case study area in the TC scenario, and 69 % in the GC scenario. Feed production per ha (net energy for lactation) was reduced by 3% for the TC and 41 % for the GC scenario. Food production on the case study area reduced to the same extent in TC, and to a larger extent (by about two thirds) in GC because no feed was imported. In consequence, biodiversity increased, thus reducing the PDF from 0.17 in the baseline scenario to 0.16 in the TC scenario and 0.10 in the GC scenario. In both scenarios, extensive grassland offset part of the loss in plant species richness caused by cropland and intensive grassland. Implementing these opposing scenarios requires different policy approaches or incentives for the dairy sector. Moreover, judging whether measures are worth the expected benefits for biodiversity depends on stakeholders’ values. Lastly, potential displacement of food production and associated impact on biodiversity needs to be considered.

Species-Richness Responses to Water-Withdrawal Scenarios and Minimum Flow Levels: Evaluating Presumptive Standards in the Tennessee and Cumberland River Basins

Water-resource managers are challenged to balance growing water demand with protecting aquatic ecosystems and biodiversity. Management decisions can benefit from improved understanding of water-withdrawal impacts on hydrologic regimes and ecological assemblages. This study used ecological limit functions for fish groups within the Tennessee and Cumberland River basins to predict species richness responses under simulated constant-rate (CR) and percent-of-flow (POF) withdrawals and for different minimum flow level protections. Streamflow characteristics (SFC) and richness were generally less sensitive to POF withdrawals than CR withdrawals among sites, fish groups, and ecoregions. Species richness generally declined with increasing withdrawals, but responses were variable depending on site-specific departures of SFCs from reference conditions, drainage area, fish group, ecoregion, and minimum flow level. Under POF withdrawals, 10% and 20% daily flow reductions often resulted in loss of <1 species and/or ≤5% richness among fish groups. Median ecological withdrawal thresholds ranged from 3.5–31% for POF withdrawals and from 0.01–0.92 m3/s for CR withdrawals across fish groups and ecoregions. Application of minimum flow level cutoffs often resulted in damping effects on SFC and richness responses, indicating that protection of low streamflows may mitigate hydrologic alteration and fish species richness loss related to water withdrawals. Site-specific and regionally summarized responses of flow regimes and fish assemblages under alternative withdrawal strategies in this study may be useful in informing water-management decisions regarding streamflow allocation and maintaining ecological flows.

Replacements of small- by large-ranged species scale up to diversity loss in Europe's temperate forest biome.

Biodiversity time series reveal global losses and accelerated redistributions of species, but no net loss in local species richness. To better understand how these patterns are linked, we quantify how individual species trajectories scale up to diversity changes using data from 68 vegetation resurvey studies of seminatural forests in Europe. Herb-layer species with small geographic ranges are being replaced by more widely distributed species, and our results suggest that this is due less to species abundances than to species nitrogen niches. Nitrogen deposition accelerates the extinctions of small-ranged, nitrogen-efficient plants and colonization by broadly distributed, nitrogen-demanding plants (including non-natives). Despite no net change in species richness at the spatial scale of a study site, the losses of small-ranged species reduce biome-scale (gamma) diversity. These results provide one mechanism to explain the directional replacement of small-ranged species within sites and thus explain patterns of biodiversity change across spatial scales.

Mitigating the Effects of Habitat Loss on Solitary Bees in Agricultural Ecosystems

Solitary bees and other wild pollinators provide an important ecosystem service which can benefit both the agricultural economy and the sustainability of many native ecosystems. Many solitary bees, however, are experiencing decreases in their populations and ranges, resulting in an overall loss of pollinator species richness in many areas. Several interacting factors have been implicated in this decline, including increased pesticide use, climate change, and pathogens, but habitat loss remains one of the primary drivers. The widespread conversion of natural habitats into agricultural landscapes has decreased the availability of adequate nesting sites and floral diversity for many bee species. Large monocultures with intensive production systems often cannot support the populations of wild bees (particularly species with short foraging ranges) necessary to ensure adequate pollination of animal-pollinated crops. Diversifying agricultural landscapes through the incorporation of wildflower plantings, as well as the preservation of remaining natural habitats, may offer a solution, as it has been shown to increase both bee diversity and abundance and the pollination of nearby crops. In this review article, we discuss the various effects of habitat loss on solitary bees and different ways to mitigate such effects in order to conserve bee diversity and populations in agricultural landscapes.

Rainforest expansion reduces understorey plant diversity and density in open forest of eastern Australia

AbstractThe expansion of rainforest pioneer trees into long‐unburnt open forests has become increasingly widespread across high rainfall regions of Australia. Increasing tree cover can limit resource availability for understorey plant communities and reduce understorey diversity. However, it remains unclear if sclerophyll and rainforest trees differ in their competitive exclusion of understory plant communities, which contain most of the floristic diversity of open forests. Here, we examine dry open forest across contrasting fire histories (burnt and unburnt) and levels of rainforest invasion (sclerophyll or rainforest midstorey) to hindcast changes in understorey plant density, richness and composition. The influence of these treatments and other site variables (midstorey structure, midstorey composition and soil parameters) on understorey plant communities were all examined. This study is the first to demonstrate significantly greater losses of understorey species richness, particularly of dry open‐forest specialists, under an invading rainforest midstorey compared to a typical sclerophyll midstorey. Rainforest pioneers displaced over half of the understorey plant species, and reduced ground cover and density of dry forest specialists by ~90%. Significant understorey declines also occurred with increased sclerophyll midstorey cover following fire exclusion, although losses were typically less than half that of rainforest‐invaded sites over the same period. Understorey declines were closely related to leaf area index and basal area of rainforest and wattle trees, suggesting competitive exclusion through shading and potentially belowground competition for water. Around 20% of displaced species lacked any capacity for population recovery, while transient seed banks or distance‐limited dispersal may hinder recovery for a further 68%. We conclude that rainforest invasion leads to significant declines in understorey plant diversity and cover in open forests. To avoid elimination of local native plant populations in open forests, fires should occur with sufficient frequency to prevent overstorey cover from reaching a level where shade‐intolerant species fail to thrive.

Symbiosis in the human gastrointestinal tract

The human body is a planet populated by myriads of microorganisms all over its surface and in cavities connected to the outside. Experimental and clinical research is showing that microbial colonizers are a functional and essential part of the human organism. The microbial ecosystem, which is housed in the gastrointestinal tract, provides a "metagenome": genes and additional functions to the genetic resources of the species, which are involved in multiple physiological processes (somatic development, nutrition, immunity, etc.). The human intestine houses lymphoid structures specialized in the induction and regulation of adaptive immunity, and the interaction of the intestinal microbiota with the immune system of the digestive mucosa plays a key role for the individual's homeostasis with the outside world. Some chronic non-communicable inflammatory diseases in developed society are associated with dysbiosis: loss of species richness in the gut microbiota and deviation from the ancestral microbial environment. Generating and maintaining diversity in the gut microbiota is a new clinical goal for health promotion and disease prevention.

Increasing temperatures, diversity loss and reorganization of deep-sea fish communities east of Greenland

In recent years, Arctic and sub-Arctic fish communities have shown extensive reorganization on shelves and in shallow waters, but little is known about the ecological impact of environmental changes in deeper waters. We examined temporal changes (1998-2016) in fish diversity and community structure based on research survey data from East Greenland, over a depth gradient spanning 400 to 1500 m. A northern and a southern continental slope region, 360 km apart, were analysed for temporal changes in water temperature and fish community structure. The bottom water temperature increased by up to 0.2 and 0.5°C, respectively. Contrary to expectations, there was a concomitant loss of species richness of up to 3 and 5 species, respectively, and a decrease in total abundance in both regions. Abundances of individual species displayed different trends between regions, with 3 species of wolf fishes (Anarhichas spp.) and American plaice Hippoglossoides platessoides decreasing in the north and blue antimora Antimora rostrata, Agassiz’ slickhead Alepocephalus agassizii and the roundnose grenadier Coryphaenoides rupestris decreasing in the south. The regional differences may reflect different oceanographic characteristics, as the northern region is more influenced by colder Arctic water, whereas the southern region is primarily influenced by the Subpolar Gyre (SPG). However, the observed temperature increase is expected to be due to an intensifying Atlantic Multidecadal Oscillation and/or anthropogenic climate change and not to SPG changes. The observed changes in biodiversity and community structure associated with warming are likely to affect community dynamics and alter ecosystem functioning.

Kelp patch size and density influence secondary productivity and diversity of epifauna

Habitat‐forming ecosystem engineers are the foundation of many marine ecosystems where they support diverse and productive food‐webs. A reduction in their patch size or density may affect the productivity, biodiversity and stability of these ecosystems. We determined the effects of different densities and patch sizes of Ecklonia radiata (the dominant kelp in southern Australia) on the secondary productivity, species richness, diversity and community structure of understory epifaunal invertebrates and how associated environmental covariates modified by kelp affected those patterns. We assessed sub‐canopy epifauna across 28 artificial reefs with transplanted E. radiata consisting of seven different patch sizes (0.12–7.68 m2) crossed with four kelp densities (0–16 kelp m−2) over two years. Epifaunal secondary productivity associated with both natural algal and standardised rope fibre habitats decreased with patch size and was elevated when kelp was absent, however, it was also high in natural habitat when there was a high density of kelp. Epifaunal productivity was positively associated with sub‐canopy light and water flow but negatively associated with the biomass of the dominant understory alga, Ulva sp. Epifaunal diversity declined with a reduction in reef size as did richness which correlated with a loss of algal species richness. Community structure of epifauna also differed between small and large reefs, between reefs with and without kelp, between rope habitats at the centre and at the edge of reefs, and within natural habitat between reefs supporting high and low densities of kelp. Overall, these results indicate complex effects of E. radiata decline on epifaunal communities, with high secondary productivity associated with dense kelp stands, but also areas without kelp that are dominated by turf algae. While the loss of standing kelp from rocky reefs may result in declines in epifaunal biodiversity, where turf algae replaces kelp, the reefs may still support high secondary productivity.