Modelling plant population size and extinction thresholds from habitat loss and habitat fragmentation: Effects of neighbouring competition and dispersal strategy

Sessile organisms, including plants and benthic macrofauna, are often restricted in the ranges over which they are able to reproduce and disperse. This leads to spatial patterning within populations, causing the effective population density around each individual to depart from the average across its range. This has important implications for population dynamics, in particular the minimum density at which populations are able to maintain positive growth (the Allee threshold). Here we compare the population dynamics of species with three syndromes -spatially restricted mating, dispersal or both -against a null model of a species with no spatial limitations. First we demonstrate mathematically that the population density at which Allee effects occur systematically shifts in each case. Next we use individual-based models representing three exemplar species to simulate the implications for the Allee threshold of each within a fixed area. In the case where mating occurs over long ranges but dispersal is restricted (e.g. the wind-pollinated silver fir, Abies alba Mill.), there is a negligible impact on the Allee threshold. When mating is also spatially restricted (e.g. the dipterocarp tree Shorea curtisii Dyer ex King), the Allee threshold reduces, unless high death rates prevent the stabilisation of aggregations. This occurs because offspring remain within the range of potential mating partners. * Corresponding author Email address: markus.eichhorn@nottingham.ac.uk (Markus P. Eichhorn) URL: treesinspace.com (Markus P. Eichhorn) Preprint submitted to Ecological Modelling May 24, 2017Finally we consider a case in which mating is short-ranged, and dispersal effectively unrestricted, but in which individuals choose to locate themselves in the vicinity of conspecifics (e.g. acorn barnacles, Semibalanus balanoides). This has the effect of maintaining clustering in the face of high dispersal, reducing the Allee threshold, and compensating for the apparent cost of short-range mating.Incorporating information on ranges of mating and dispersal can lead to more effective models for the management of populations at low density, in particular the identification of species with syndromes which make them vulnerable to Allee effects. Most notably, mechanisms which increase the degree of clustering in populations increase both their resilience and persistence when finding a mate is the greatest challenge faced by a sessile organism.

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“…This contradicts the conventional intuition that well-dispersed species should be favoured under such conditions (but see (Liao et al, 2013)). …”

contrasting

confidence: 52%

Relative ranges of mating and dispersal modulate Allee thresholds in sessile species

Velázquez-Castro

Eichhorn

2017

Ecological Modelling

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“…Gaussian kernel). However, our results should be considered as representative for two extreme dispersal modes that delimit the continuum in between, because both types of dispersal have long been used to simplify ecological models, yielding approximately the same results as more realistic dispersal [33,34,[51][52][53][54][55].…”

Section: Discussionmentioning

confidence: 99%

“…Note that, compared with the spatial aggregation of disturbance, the spatial aggregation of habitat fragments has completely opposite (i.e. positive) effects on species persistence, because connected habitats provide more opportunities for local recolonization [33,34,49]. Spatial correlation in disturbance led to different competitive outcomes, depending on how much area was disturbed (figures 2 and 3).…”

Section: Discussionmentioning

confidence: 99%

“…In equation (2.1b), the first term on the right side represents the growth of species 2 via seed random dispersal, where (1 2 r 1 2 r 2 ) ¼ r 0 is the fraction of unoccupied sites in the entire landscape. Note that we only consider seeds landing on empty sites and ignore those landing on already occupied sites [33,34]. Similar to species 1, the death of species 2 also includes both intrinsic mortality and the enhanced mortality induced by both intra-and interspecific competition.…”

Section: ð2:1bþmentioning

confidence: 99%

“…In this study, we model species dynamics in the face of spatially correlated periodic disturbance by using a pair approximation (PA) approach, which has been shown to be useful in characterizing spatial neighbouring correlation between adjacent sites in lattice-structured models [28][29][30][31][32][33][34][35]. Because we expect the spatial aggregation of disturbance to interact with dispersal strategy, we consider two extremes of plant species dispersal: distance-limited, vegetative, clonal spread (local dispersal [36,37]) and long-range, wind-based seed dispersal (global dispersal [38][39][40]), with local dispersal being restricted to neighbouring sites and global dispersal being uniformly random across the entire landscape.…”

Section: Introductionmentioning

confidence: 99%

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Coexistence of species with different dispersal across landscapes: a critical role of spatial correlation in disturbance

et al. 2016

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Disturbance is key to maintaining species diversity in plant communities. Although the effects of disturbance frequency and extent on species diversity have been studied, we do not yet have a mechanistic understanding of how these aspects of disturbance interact with spatial structure of disturbance to influence species diversity. Here we derive a novel pair approximation model to explore competitive outcomes in a two-species system subject to spatially correlated disturbance. Generally, spatial correlation in disturbance favoured long-range dispersers, while distance-limited dispersers were greatly suppressed. Interestingly, high levels of spatial aggregation of disturbance promoted long-term species coexistence that is not possible in the absence of disturbance, but only when the local disperser was intrinsically competitively superior. However, spatial correlation in disturbance led to different competitive outcomes, depending on the disturbed area. Concerning ecological conservation and management, we theoretically demonstrate that introducing a spatially correlated disturbance to the system or altering an existing disturbance regime can be a useful strategy either to control species invasion or to promote species coexistence. Disturbance pattern analysis may therefore provide new insights into biodiversity conservation.

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Critical transitions and evolutionary hysteresis in movement: Habitat fragmentation can cause abrupt shifts in dispersal that are difficult to revert

Jager

Soons

2023

Ecology and Evolution

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Modelling plant population size and extinction thresholds from habitat loss and habitat fragmentation: Effects of neighbouring competition and dispersal strategy

Cited by 51 publications

References 44 publications

Relative ranges of mating and dispersal modulate Allee thresholds in sessile species

Relative ranges of mating and dispersal modulate Allee thresholds in sessile species

Coexistence of species with different dispersal across landscapes: a critical role of spatial correlation in disturbance

Critical transitions and evolutionary hysteresis in movement: Habitat fragmentation can cause abrupt shifts in dispersal that are difficult to revert

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