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Habitat Destruction and the Extinction Debt

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Abstract

HABITAT destruction is the major cause of species extinctions1–3. Dominant species often are considered to be free of this threat because they are abundant in the undisturbed fragments that remain after destruction. Here we describe a model that explains multispecies coexistence in patchy habitats4 and which predicts that their abundance may be fleeting. Even moderate habitat destruction is predicted to cause time-delayed but deterministic extinction of the dominant competitor in remnant patches. Further species are predicted to become extinct, in order from the best to the poorest competitors, as habitat destruction increases. More-over, the more fragmented a habitat already is, the greater is the number of extinctions caused by added destruction. Because such extinctions occur generations after fragmentation, they represent a debt—a future ecological cost of current habitat destruction.
... Early work in this area by Nee and May [1] analyzed the effect of habitat removal of two species that are regionally abundant. Later, Tilman et al. [2] developed the coexistence model, which became widely applied to competitive multi-species' habitat loss. In the Tilman study, extinction in abundant species may be due to habitat loss with time delay. ...
... The parameters used are similar to Tilman's input parameters and three types of destruction were simulated: instantaneous destruction, continuous-complete destruction, and continuous-partial destruction. With a slight modification to the model in Tilman et al. [2], the direct effects of habitat destruction on species abundance are captured. Weak and strong Al-lee-like effects are studied in Chen et al. [24] whose work is also based on Tilman's model with a drastically shortened time delay of the species extinction. ...
... A special case when m i = m, ∀i ∈ {1, 2, . . . , n} studied in Tilman et al. [2,3] and Liu et al. [23], if the ith species survives, all other higher ranked species will also survive the habitat destruction. ...
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We studied the N-species competitive coexistence model with direct effect on habitat destruction to analyze the behaviors of abundant and extinct species in the system caused by habitat loss. The nontrivial equilibrium points of the system are determined for a general habitat destruction function. For the trivial equilibrium, species that survived the habitat destruction are identified using eigenvalues of the Jacobian matrix. Solutions of the system are also presented using the recursive method. Three special cases of habitat destruction functions are addressed: continuous destruction, which is a typical habitat destruction; sudden habitat destruction, which is similar to natural phenomena such as earthquakes or floods; and sudden habitat destruction with aftershocks. The proportional abundances of 50 species are numerically portrayed in each case. We found that the survival of a species is guaranteed if its corresponding eigenvalue is positive. However, the fact that a species has negative corresponding eigenvalue does not guarantee its extinction, as this also depends on the initial number of that species.
... Forests throughout the world have undergone several major changes that affect entire ecosystems and will have lasting impacts on their overall health. These changes include dominant species loss, habitat destruction and exotic species introductions and invasions, each of which greatly alter ecosystem functioning (Tilman et al. 1994; Pyšek and Richardson 2010). In the Midwestern and Eastern United States, forests are greatly impacted by the introduction of the insect, Agrilus planipennis (emerald ash borer; EAB), which has signi cantly decreased the abundance of Fraxinus spp. ...
... Invasive species are detrimental to forests by causing habitat degradation, altering plant community structure, and impacting ecosystem functions (Tilman et al. 1994;Pyšek and Richardson 2010). The invasion of honeysuckle and EAB both independently disrupt ecosystem functions, but their interactive effect on ecosystems is relatively unknown. ...
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Midwestern forests are currently impacted by two prominent invaders, the Emerald Ash Borer (EAB), Agrilus planipennis and Amur honeysuckle, Lonicera maackii . The loss of ash ( Fraxinus spp.) trees due to EAB invasion can further facilitate honeysuckle invasion, driving changes in the composition of forest leaf litter. To evaluate the extent to which these changes alter ecosystem function, we conducted litter bag and culture-based decomposition experiments using leaf litter from sugar maple ( Acer saccharum ), oak ( Quercus spp.), black ash ( Fraxinus nigra ), green ash ( Fraxinus pennsylvanica ), spicebush ( Lindera benzoin ), and Amur honeysuckle (Lonicera maackii) . To further understand the mechanism driving differences in decay rates, we inoculated six species of decomposing fungi separately onto both single species and multispecies (half honeysuckle and half native species) leaf litter and measured decomposition rate, fungal growth and enzymatic activity in laboratory-based cultures. Honeysuckle leaf litter decomposed faster, had increased fungal growth, and had higher activity for carbon degrading enzymes compared to native species leaf litter. Furthermore, multispecies mixtures followed the same patterns as honeysuckle, suggesting that the addition of honeysuckle to leaf litter will accelerate ecosystem functions related to carbon breakdown. Consequently, forests that experience the invasion of honeysuckle and EAB induced loss of ash are likely to have faster rates of decomposition, potentially resulting in an influx of available nutrients.
... The effect size for fragmented meta-communities was small, but there could be several reasons, it represents a lower limit. It is possible that the landscapes analyzed have not yet reached equilibrium, in which case the small negative effect size could partly reflect an unpaid extinction debt in small patches (Tilman et al. 1994). Other ecological considerations also might reduce the observed effect size, for example, perhaps species dependent upon larger patches were rapidly lost following fragmentation (Gibson et al. 2013) or the contrast between habitat and the surrounding matrix was not pronounced, reducing the impacts of fragmentation on the taxa concerned (Laurance et al. 2011). ...
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Although groups of small habitat patches often support more species than large patches of equal total area, their biodiversity value remains controversial. An important line of evidence in this debate compares species accumulation curves, where patches are ordered from small–large and large–small (aka ‘SLOSS analysis’). However, this method counts species equally and is unable to distinguish patch size dependence in species’ occupancies. Moreover, because of the species–area relationship, richness differences typically only contribute to accumulation in small–large order, maximizing the probability of adding species in this direction. Using a null model to control for this, I tested 202 published datasets from archipelagos, habitat islands and fragments for patch size dependence in species accumulation and compared conclusions regarding relative species accumulation with SLOSS analysis. Relative to null model expectations, species accumulation was on average 2.7% higher in large–small than small–large order. The effect was strongest in archipelagos (5%), intermediate for fragments (1.5%) and smallest for habitat islands (1.1%). There was no difference in effect size among taxonomic groups, but each shared this same trend. Results suggest most meta-communities include species that either prefer, or depend upon, larger habitat patches. Relative to SLOSS analysis, null models found lower frequency of greater small-patch importance for species representation (e.g., for fragments: 69 vs 16% respectively) and increased frequency for large patches (fragments: 3 vs 25%). I suggest SLOSS analysis provides unreliable inference on species accumulation and the outcome largely depends on island species–area relationships, not the relative diversity value of small vs large patches.
... Standard approaches for identifying refugia involve integrating data on habitat characteristics 448 (e.g., resource availability, climatic conditions) that support species persistence with species 449 distribution data over relevant spatial and temporal scales (Keppel et al., 2012, Morelli et al., 450 2020). Dynamic molecular markers like changes in gene expression complement this framework 451 because they can reflect the health of populations long before population declines are detected 452 (Tilman et al., 1994). This study provides evidence that gene expression can also be used to look 453 for evidence of refugia, which is a complementary approach to more standard methods. ...
Preprint
As anthropogenic change continues to impact global biodiversity, the importance of rapidly identifying biodiversity refugia cannot be overstated. In this study, we employed a molecular test of the hypothesis that mountains serve as refugia for bumble bees against anthropogenic stressors. To explore this hypothesis, we compared stress-related patterns of gene expression in the brains of wild, pollen-foraging bumble bees of two species, B. vosnesenskii and B. melanopygus, collected at different elevations throughout the Sierra Nevada Mountain range in California, USA. We found evidence that the expression of several immune and detoxification genes is associated with elevational differences. This suggests that bees are experiencing differential exposure to stressors along an elevational gradient, which is an important criterion for identifying refugia across dynamic and heterogenous environments. This study thus provides evidence that mountains may serve as refugia for bumble bees in response to anthropogenic stressors, as has been detected for many other organisms.
... In the context of changes to the physical landscape, the time lag literature is centered around 'extinction debt', and more recently 'extinction credit'. These ideas posit that a loss or change of habitat amount or configuration may result in a decline in species richness or the extirpation of populations ('debt') or increase in species richness ('credit') that are not immediately realized, but instead take some amount of relaxation time that varies based on life history traits and the magnitude of the habitat change(Diamond 1972;Tilman et al. 1994;Watts et al. 2020). Typical response variables are broad metrics such as species richness(Metzger et al. 2009; Wearn et al. 2012;Chen and Peng 2017), measured in unpaid debt (e.g.Montgomery et al. 2020) or extinction half-life of communities (time until half the resident species are lost)(Gibson et al. 2013;Halley et al. 2016). ...
Thesis
Anthropogenic habitat destruction is one of the major causes of biodiversity loss, driving species declines across the planet. The resultant human-modified landscapes are not detrimental for all species. Some species such as small to medium-sized habitat generalist carnivores (hereafter referred to as ‘mesocarnivores’) are able to thrive because of the exclusion of natural enemies and anthropogenic sources of food. With the benefits of human-modified landscapes come novel threats, such as increased exposure to hunting and introduced antagonists. Mesocarnivores may respond to these threats with changes in space and time use, with potential consequences for species interactions. In this dissertation, I examine how drivers of mesocarnivore space and time use align with physical characteristics of the human-modified landscape and associated factors, and what implications these results have for interactions between native species. I do this using empirical work across two temperate systems (Chapters II, III, and IV), and a simulation model (Chapter V).
... The rapid increases in overall R function diversity may reflect extinction debts observed in ecological systems, where the actual loss of species can be delayed for decades beyond the change in conditions that is driving extinction [Tilman et al., 1994]. This pattern has been observed as a lag between initial dilation and subsequent contraction of natural languages [Petersen et al., 2012a], particularly those requiring specialized terms like scientific English [Degaetano-Ortlieb and Teich, 2022]. ...
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Change in language use is driven by cultural forces; it is unclear whether that extends to programming languages. They are designed to be used by humans, but interaction with computer hardware rather than a human audience may limit opportunities for evolution of the lexicon of used terms. I tested this in R, an open source, mature and commonly used programming language for statistical computing. In corpus of 360,321 GitHub repositories published between 2014 and 2021, I extracted 168,857,044 function calls to act as n-grams of the R language. Over the eight-year period, R rapidly diversified and underwent substantial lexical change, driven by increasing popularity of the tidyverse collection of community packages. My results provide evidence that users can influence the evolution of programming languages, with patterns that match those observed in natural languages and reflect genetic evolution. R's evolution may have been driven by increased analytic complexity, driving new users to R, creating both selective pressure for an alternate lexicon and accompanying advective change. The speed and magnitude of this change may have flow-on consequences for the readability and continuity of analytic and scientific inquiries codified in R and similar languages.
... We suspect this is true in the Florida Panhandle Representative Unit where large tracts of potentially suitable habitat exist without contemporary DRCO records (Enge et al. 2013). Many other species also show signatures of past landscape conditions in their contemporary distributions (Lindborg and Eriksson 2004;Waldron et al. 2008;Halstead et al. 2014) and other studies have noted lags in population responses to past landscape changes (Tilman et al. 1994;Metzger et al. 2009). ...
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