Land‐use transformation is one of the most important and pervasive ecological changes occurring across the Earth, but its long‐term effects are poorly understood. Here, we analyze the effects of urban and agriculture development on bird biodiversity and community structure over a 16‐yr study period. We found that long‐term effects of land‐use change are dependent on spatial scale and land‐use type. At the regional scale, we found that gamma diversity (total number of species observed) declined by ~10% over time. At the landscape spatial scale, we found that beta diversity (uniqueness of bird communities) increased by ~16% over time. Additionally, the average contributions of urban riparian bird communities to beta diversity were generally the highest but declined by ~26% over the study period. Contributions of urban communities to beta diversity were generally the lowest but increased by ~10% over time. At the local scale, we observed different responses for different measures of alpha diversity. For bird species richness, temporal changes varied by land use. Species richness declined 16% at sites in desert riparian areas but increased by 21% and 12% at sites in urban and agricultural areas, respectively. Species evenness declined across all land uses, with some land uses experiencing more rapid declines than others. Our analysis of species groups that shared certain traits suggests that these community‐level changes were driven by species that are small, breed onsite, and feed on insects, grains, and nectar. Collectively, our results suggest that biodiversity declines associated with land‐use change predominate at the regional and local spatial scale, and that these effects can strengthen or weaken over time. However, these changes counterintuitively led to increases in biodiversity at the landscape scale, as bird communities became more unique. This has implications for conservation and management as it shows that the effects of land‐use modification on biodiversity may be positive or negative depending on the spatial scale considered.
Climate and land‐use changes are thought to be the greatest threats to biodiversity, but few studies have directly measured their simultaneous impacts on species distributions. We used a unique historic resource—early 20th‐century bird surveys conducted by Joseph Grinnell and colleagues—paired with contemporary resurveys a century later to examine changes in bird distributions in California's Central Valley, one of the most intensively modified agricultural zones in the world and a region of heterogeneous climate change. We analyzed species‐ and community‐level occupancy using multispecies occupancy models that explicitly accounted for imperfect detection probability, and developed a novel, simulation‐based method to compare the relative influences of climate and land‐use covariates on site‐level species richness and beta diversity (measured by Jaccard similarity). Surprisingly, we show that mean occupancy, species richness and between‐site similarity have remained remarkably stable over the past century. Stability in community‐level metrics masked substantial changes in species composition; occupancy declines of some species were equally matched by increases in others, predominantly species with generalist or human‐associated habitat preferences. Bird occupancy, richness and diversity within each era were driven most strongly by water availability (precipitation and percent water cover), indicating that both climate and land‐use are important drivers of species distributions. Water availability had much stronger effects than temperature, urbanization and agricultural cover, which are typically thought to drive biodiversity decline.
more » « less- NSF-PAR ID:
- 10078044
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 24
- Issue:
- 12
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 5882-5894
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Global tropical forests have been modified and fragmented by commodity agroforests, leading to significant alterations in ecological communities. Nevertheless, these production landscapes offer secondary habitats that support and sustain local biodiversity. In this study, we assess community level and species‐specific responses of amphibians to land management in areca, coffee and rubber, three of the largest commodity agroforests in the Western Ghats.
A total of 106 agroforests across a 30,000‐km2landscape were surveyed for amphibians using a combination of visual and auditory encounter surveys. We used a Bayesian multi‐species occupancy modelling framework to examine patterns of species richness, beta diversity, dominance structure and individual species occupancies. The influence of biogeographic variables such as elevation and latitude as well as microhabitat availability of streams, ponds and unpaved plantation roads was tested on amphibian species occupancy.
Coffee agroforests had the highest species richness and lowest dominance when compared to areca and rubber. Beta diversity was highest in areca for within agroforest measures. Compared across agroforests, coffee had highest beta diversity with areca and rubber. Both elevation and latitude showed an overall positive association with amphibian occupancy, although species‐specific responses varied considerably.
Microhabitat availability was one of the strongest predictors of amphibian occupancy, with mean community response being positive with presence of water bodies and roads. Pond presence increased species richness per site by 34.7% (species‐specific responses in occupancy ranged from –2.7% to 327%). Stream presence alone did not change species richness but species‐specific response ranged from –59% to 273%. Presence of plantation roads also increased species richness by 21.5% (species‐specific response ranged from –82% to 656%). Being unpaved with little vehicular traffic, plantation roads seem to provide additional habitats for amphibians. Presence of all three microhabitats at a site increased species richness by 75%.
Our study highlights the importance of land management strategies that maintain diverse native canopy and freshwater bodies and other microhabitats in sustaining amphibian fauna. Market‐driven land‐use change from coffee to other agroforest types will have detrimental effects on amphibian communities and their long‐term sustainability in the Western Ghats.
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Abstract Human impacts have led to dramatic biodiversity change which can be highly scale‐dependent across space and time. A primary means to manage these changes is via passive (here, the removal of disturbance) or active (management interventions) ecological restoration. The recovery of biodiversity, following the removal of disturbance, is often incomplete relative to some kind of reference target. The magnitude of recovery of ecological systems following disturbance depends on the landscape matrix and many contingent factors. Inferences about recovery after disturbance and biodiversity change depend on the temporal and spatial scales at which biodiversity is measured.
We measured the recovery of biodiversity and species composition over 33 years in 17 temperate grasslands abandoned after agriculture at different points in time, collectively forming a chronosequence since abandonment from 1 to 80 years. We compare these abandoned sites with known agricultural land‐use histories to never‐disturbed sites as relative benchmarks. We specifically measured aspects of diversity at the local plot‐scale (α‐scale, 0.5 m2) and site‐scale (γ‐scale, 10 m2), as well as the within‐site heterogeneity (β‐diversity) and among‐site variation in species composition (turnover and nestedness).
At our α‐scale, sites recovering after agricultural abandonment only had 70% of the plant species richness (and ~30% of the evenness), compared to never‐ploughed sites. Within‐site β‐diversity recovered following agricultural abandonment to around 90% after 80 years. This effect, however, was not enough to lead to recovery at our γ‐scale. Richness in recovering sites was ~65% of that in remnant never‐ploughed sites. The presence of species characteristic of the never‐disturbed sites increased in the recovering sites through time. Forb and legume cover declines in years since abandonment, relative to graminoid cover across sites.
Synthesis. We found that, during the 80 years after agricultural abandonment, old fields did not recover to the level of biodiversity in remnant never‐ploughed sites at any scale. β‐diversity recovered more than α‐scale or γ‐scale. Plant species composition recovered, but not completely, over time, and some species groups increased their cover more than others. Patterns of ecological recovery in degraded ecosystems across space and long time‐scales can inform targeted active restoration interventions and perhaps, lead to better outcomes. -
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<styled-content style='fixed-case'>A</styled-content>bstract Evidence regarding the ability of agroforests to conserve biological diversity has been mixed; they tend to maintain avian communities with species richness similar to that of undisturbed forest ecosystems but generally do not completely preserve community composition. Using a combination of occupancy modeling and non‐metric multidimensional scaling on point‐count data, we assessed changes in avian community diversity and composition along a successional gradient in traditional Lacandon Maya agroforests and compared them to protected areas in the region. Bird species richness and diversity in Lacandon agroforests peaked in early secondary forest stages. These agroforests' mean Shannon–Weiner diversity was 5% higher than that of nearby protected areas, but their species richness was similar. Community composition in Lacandon agroforests changed throughout succession, with earlier stages supporting communities distinctly characterized by generalist species, while subsequent, less‐intensively managed stages tended to support more forest‐dwellers. The bird community observed in even the most mature secondary forest stages in Lacandon agroforests differed from that of undisturbed rain forest ecosystems. These results demonstrate the potential of traditional Lacandon agroforestry management to conserve avian biodiversity while ensuring food sovereignty for farmers. However, because the community composition of early‐successional stages was different than later stages, shortening fallow cycles and reducing forest cover to increase agricultural production will limit the species this system can support. This study illustrates the value of incorporating traditional agroecosystems into conservation planning as well as maintaining protected areas, because the latter serve as refugia for species that require undisturbed forest habitat in an agroecological matrix.
Abstract in Spanish is available with online material.
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Abstract The outcome of the ongoing biodiversity crisis depends on the capacity of the Earth’s wildlife to persist in working landscapes. Yet, the species that occupy working landscapes are often distinct from those in protected areas, with a large group of “sensitive species” thought to rarely venture into human‐dominated landscapes. As governments have committed to restoring degraded lands world‐wide, determining whether and how working landscapes can be restored to benefit sensitive species remains a major challenge.
We surveyed Neotropical birds across Northwestern Costa Rica in protected areas, farms and forests embedded within working landscapes. We analysed community composition to understand how gradients of forest cover, fragmentation and regional precipitation determine how conserving (or restoring) tropical forests in working landscapes could safeguard entire communities, especially sensitive species with limited ranges.
We found agricultural sites maintained relatively high bird diversity but hosted very distinct communities from those found in protected areas. The average range size of species found in agricultural communities was double the size of species in protected areas. However, high forest cover sites in working landscapes housed bird communities with small range sizes that were equivalent to those in nearby protected areas, despite being twice as fragmented and significantly more disturbed.
The effect of local forest cover on bird composition was contingent on both landscape context and regional climate. When local forest cover increased in wetter regions and more forested landscapes, bird communities in working landscapes exhibited a stronger shift towards the assemblages found in protected areas. Specifically, we found that reforesting the wettest sites would increase similarity to protected areas fourfold compared to only a twofold increase in the driest sites.
Synthesis and applications. Despite experiencing much more fragmentation and degradation than protected areas, forests in Costa Rican working landscapes can maintain bird communities that strongly resemble those found in protected areas. This suggests that conserving or restoring forests in working landscapes, particularly within wetter regions and already forested landscapes, may safeguard bird communities when creating protected areas is infeasible.
