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1. Ecology and life history predict avian nest success in the global tropics

   https://doi.org/10.1073/pnas.2402652121  

   Smart, Zachariah Fox; Downing, Philip A; Austin, Suzanne H; Greeney, Harold F; Londoño, Gustavo A; Nahid, Mominul I; Robinson, W Douglas; Riehl, Christina (November 2024, Proceedings of the National Academy of Sciences)

   Nest predation rates critically influence avian biodiversity and evolution. In the north temperate zone, increased nest failure along edges of forest fragments is hypothesized to play a major role in the disappearance of bird species from disturbed landscapes. However, we lack comprehensive syntheses from tropical latitudes, where biodiversity is highest and increasingly threatened by habitat fragmentation and disturbance. We assembled data from five decades of field studies across the global tropics (1,112 populations of 661 species) and used phylogenetic models to evaluate proposed predictors of nest success. We found significant effects of several traits, including adult body mass and nest architecture. Contrary to results from many temperate locations, anthropogenic habitat disruption did not consistently reduce nest success; in fact, raw nest success rates were lower in large tracts of primary forest than in disturbed or fragmented landscapes. Follow-up analyses within species, using a subset of 76 species for which we had estimates of nest survival in habitats with different levels of disruption, confirmed that neither disturbance nor fragmentation significantly influenced nest success. These results suggest that nest predation alone cannot explain observed declines in avian biodiversity in tropical forest fragments, raising new questions about the demographic processes that drive extinction in the tropics. 

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2. Extinction of biotic interactions due to habitat loss could accelerate the current biodiversity crisis

   https://doi.org/10.1002/eap.2608  

   Sandor, Manette E.; Elphick, Chris S.; Tingley, Morgan W. (June 2022, Ecological Applications)

   Abstract Habitat loss disrupts species interactions through local extinctions, potentially orphaning species that depend on interacting partners, via mutualisms or commensalisms, and increasing secondary extinction risk. Orphaned species may become functionally or secondarily extinct, increasing the severity of the current biodiversity crisis. While habitat destruction is a major cause of biodiversity loss, the number of secondary extinctions is largely unknown. We investigate the relationship between habitat loss, orphaned species, and bipartite network properties. Using a real seed dispersal network, we simulate habitat loss to estimate the rate at which species are orphaned. To be able to draw general conclusions, we also simulate habitat loss in synthetic networks to quantify how changes in network properties affect orphan rates across broader parameter space. Both real and synthetic network simulations show that even small amounts of habitat loss can cause up to 10% of species to be orphaned. More area loss, less connected networks, and a greater disparity in the species richness of the network's trophic levels generally result in more orphaned species. As habitat is lost to land‐use conversion and climate change, more orphaned species increase the loss of community‐level and ecosystem functions. However, the potential severity of repercussions ranges from minimal (no species orphaned) to catastrophic (up to 60% of species within a network orphaned). Severity of repercussions also depends on how much the interaction richness and intactness of the community affects the degree of redundancy within networks. Orphaned species could add substantially to the loss of ecosystem function and secondary extinction worldwide. 

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3. Demography of the understory herb Heliconia acuminata (Heliconiaceae) in an experimentally fragmented tropical landscape

   https://doi.org/10.5061/dryad.stqjq2c8d  

   Bruna, Emilio; Uriarte, María; Darrigo, Maria Rosa; Rubim, Paulo; Jurinitz, Cristiane; Scott, Eric; Ferreira da Silva, Osmaildo; Kress, John W.; Dynamics, Biological of (January 2023, Dryad)

   Habitat fragmentation remains a major focus of research by ecologists decades after being put forward as a threat to the integrity of ecosystems. While studies have documented myriad biotic changes in fragmented landscapes, including the local extinction of species from fragments, the demographic mechanisms underlying these extinctions are rarely known. However, many of them – especially in lowland tropical forests – are thought to be driven by one of two mechanisms: (1) reduced recruitment in fragments resulting from changes in the diversity or abundance of pollinators and seed dispersers or (2) increased rates of individual mortality in fragments due to dramatically altered abiotic conditions, especially near fragment edges. Unfortunately, there have been few tests of these potential mechanisms due to the paucity of long-term and comprehensive demographic data collected in both forest fragments and continuous forest sites. Here we report 11 years (1998-2009) of demographic data from populations of the Amazonian understory herb Heliconia acuminata (LC Rich.) found at Brazil’s Biological Dynamics of Forest Fragments Project (BDFFP). The resulting data set comprises 66000 plant×year records of 8586 plants, including 3464 seedlings that became established after the initial census. Seven populations were in experimentally isolated fragments (one in each of four 1-ha fragments and one in each of three 10-ha fragments), with the remaining six populations in continuous forest. Each population was in a 50×100m permanent plot, with the distance between plots ranging from 500 m-60 km. The plants in each plot were censused annually, at which time we recorded, identified, marked, and measured new seedlings, identified any previously marked plants that died, and recorded the size of surviving individuals. Each plot was also surveyed 4-5 times during the flowering season to identify reproductive plants and record the number of inflorescences each produced. These data have been used to investigate topics ranging from the way fragmentation-related reductions in germination influence population dynamics to statistical methods for analyzing reproductive rates. This breadth of prior use reflects the value of these data to future researchers. In addition to analyses of plant responses to habitat fragmentation, these data can be used to address fundamental questions in plant demography, the evolutionary ecology of tropical plants, and for developing and testing demographic models and tools. Though we welcome opportunities to collaborate with interested users, there are no restrictions on the use this data set. However, we do request that those using the data for teaching or research inform us of how they are doing so and cite this paper and the data archive when appropriate. Any publication using the data must also include a BDFFP Technical Series Number in the Acknowledgments. Authors can request this series number upon the acceptance of their article by contacting the BDFFP’s Scientific Coordinator or E. M. Bruna. 

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4. Fragmentation disrupts microbial effects on native plant community productivity

   https://doi.org/10.1111/1365-2745.14097  

   Kiesewetter, Kasey N.; Otano, Leydiana; Afkhami, Michelle E. (April 2023, Journal of Ecology)

   Abstract Anthropogenic habitat fragmentation—the breaking up of natural landscapes—is a pervasive threat to biodiversity and ecosystem function world‐wide. Fragmentation results in a mosaic of remnant native habitat patches embedded in human‐modified habitat known as the ‘matrix’. By introducing novel environmental conditions in matrix habitats and reducing connectivity of native habitats, fragmentation can dramatically change how organisms experience their environment. The effects of fragmentation can be especially important in urban landscapes, which are expanding across the globe. Despite this surging threat and the importance of microbiomes for ecosystem services, we know very little about how fragmentation affects microbiomes and even less about their consequences for plant–microbe interactions in urban landscapes.By combining field surveys, microbiome sequencing and experimental mesocosms, we (1) investigated how microbial community diversity, composition and functional profiles differed between 15 native pine rockland fragments and the adjacent urban matrix habitat, (2) identified habitat attributes that explained significant variation in microbial diversity of native core habitat compared to urban matrix and (3) tested how changes in urbanized and low connectivity microbiomes affected plant community productivity.We found urban and native microbiomes differed substantively in diversity, composition and functional profiles, including symbiotic fungi decreasing 81% and pathogens increasing 327% in the urban matrix compared to native habitat. Furthermore, fungal diversity rapidly declined as native habitats became increasingly isolated, with ~50% of variation across the landscape explained by habitat connectivity alone. Interestingly, microbiomes from native habitats increased plant productivity by ~300% while urban matrix microbiomes had no effect, suggesting that urbanization may decouple beneficial plant–microbe interactions. In addition, microbial diversity within native habitats explained significant variation in plant community productivity, with higher productivity linked to more diverse microbiomes from more connected, larger fragments.Synthesis. Taken together, our study not only documents significant changes in microbial diversity, composition and functions in the urban matrix, but also supports that two aspects of habitat fragmentation—the introduction of a novel urban matrix and reduced habitat connectivity—disrupt microbial effects on plant community productivity, highlighting preservation of native microbiomes as critical for productivity in remnant fragments. 

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5. Demography of the understory herb H eliconia acuminata ( H eliconiaceae) in an experimentally fragmented tropical landscape

   https://doi.org/10.1002/ecy.4174  

   Bruna, Emilio M.; Uriarte, María; Darrigo, Maria Rosa; Rubim, Paulo; Jurinitz, Cristiane F.; Scott, Eric R.; Ferreira da Silva, Osmaildo; Kress, W. John (November 2023, Ecology)

   Abstract Habitat fragmentation remains a major focus of research by ecologists decades after being put forward as a threat to the integrity of ecosystems. While studies have documented myriad biotic changes in fragmented landscapes, including the local extinction of species from fragments, the demographic mechanisms underlying these extinctions are rarely known. However, many of them—especially in lowland tropical forests—are thought to be driven by one of two mechanisms: (1) reduced recruitment in fragments resulting from changes in the diversity or abundance of pollinators and seed dispersers or (2) increased rates of individual mortality in fragments due to dramatically altered abiotic conditions, especially near fragment edges. Unfortunately, there have been few tests of these potential mechanisms due to the paucity of long‐term and comprehensive demographic data collected in both forest fragments and continuous forest sites. Here we report 11 years (1998–2009) of demographic data from populations of the Amazonian understory herbHeliconia acuminata(LC Rich.) found at Brazil's Biological Dynamics of Forest Fragments Project (BDFFP). The data set comprises >66,000 plant × year records of 8586 plants, including 3464 seedlings established after the first census. Seven populations were in experimentally isolated fragments (one in each of four 1‐ha fragments and one in each of three 10‐ha fragments), with the remaining six populations in continuous forest. Each population was in a 50 × 100 m permanent plot, with the distance between plots ranging from 500 m to 60 km. The plants in each plot were censused annually, at which time we recorded, identified, marked, and measured new seedlings, identified any previously marked plants that died, and recorded the size of surviving individuals. Each plot was also surveyed four to five times during the flowering season to identify reproductive plants and record the number of inflorescences each produced. These data have been used to investigate topics ranging from the way fragmentation‐related reductions in germination influence population dynamics to statistical methods for analyzing reproductive rates. This breadth of prior use reflects the value of these data to future researchers. In addition to analyses of plant responses to habitat fragmentation, these data can be used to address fundamental questions in plant demography and the evolutionary ecology of tropical plants and to develop and test demographic models and tools. Though we welcome opportunities to collaborate with interested users, there are no restrictions on the use of this data set. However, we do request that those using the data for teaching or research purposes inform us of how they are doing so and cite this paper and the data archive when appropriate. Any publication using the data must also include a BDFFP Technical Series Number in the Acknowledgments. Authors can request this series number upon the acceptance of their article by contacting the BDFFP's Scientific Coordinator or E. M. Bruna. 

   more » « less