Unravelling the relative roles of top‐down and bottom‐up forces driving population change in an oceanic predator

Horswill, Catharine; Ratcliffe, Norman; Green, Jonathan A.; Phillips, Richard A.; Trathan, Philip N.; Matthiopoulos, Jason

doi:10.1002/ecy.1452

Cited by 40 publications

(35 citation statements)

References 56 publications

(84 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…, Horswill et al. ). Predator‐driven effects have been viewed as the dominant force in many systems, including intertidal (Paine ), freshwater (Carpenter et al.…”

Section: Introductionmentioning

confidence: 99%

“…Communities are structured by three primary factors: predation (top-down), resources (bottom-up), or competition (parallel; Pimm et al 1985, McQueen et al 1986). How these factors interact and influence communities has been extensively studied in a variety of systems (Hairston et al 1960, Power 1992, Ernest et al 2000, Horswill et al 2016). Predator-driven effects have been viewed as the dominant force in many systems, including intertidal (Paine 1966), freshwater (Carpenter et al 1985), and terrestrial (Hairston et al 1960).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Prey‐driven control of predator assemblages: zooplankton abundance drives aquatic beetle colonization

Pintar

Resetarits

2017

Ecology

View full text Add to dashboard Cite

Trophic interactions are critical determinants of community structure and ecosystem function. In freshwater habitats, top predators are traditionally viewed as drivers of ecosystem structure, shaping populations of consumers and primary producers. The temporary nature of small water bodies makes them dependent on colonization by many organisms, particularly insects that form highly diverse predator assemblages. We conducted mesocosm experiments with naturally colonizing populations of aquatic beetles to assess how prey (zooplankton) abundances influenced colonization and assemblages of natural populations of aquatic beetles. We experimentally demonstrate that zooplankton populations can be proximate regulators of predator populations and assemblages via prey-density-dependent predator recruitment. Our results provide support for the importance of prey populations in structuring predator populations and the role of habitat selection in structuring communities. We indicate that traditional views of predators as drivers of ecosystem structure in many systems may not provide a comprehensive picture, particularly in the context of highly disturbed or ephemeral habitats.

show abstract

“…, Horswill et al. ). Predator‐driven effects have been viewed as the dominant force in many systems, including intertidal (Paine ), freshwater (Carpenter et al.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Prey‐driven control of predator assemblages: zooplankton abundance drives aquatic beetle colonization

Pintar

Resetarits

2017

Ecology

View full text Add to dashboard Cite

show abstract

“…Great differences in the ecological drivers at a local scale may occur, and it would be interesting in the near future to quantify their relative importance acting through different demographic rates (Horswill et al. ).…”

Section: Discussionmentioning

confidence: 99%

“…Other local factors, including food availability or predators, may affect other fitness parameters such as fertility (Oro et al 1999). Great differences in the ecological drivers at a local scale may occur, and it would be interesting in the near future to quantify their relative importance acting through different demographic rates (Horswill et al 2016).…”

Section: Discussionmentioning

confidence: 99%

Immature survival, fertility, and density dependence drive global population dynamics in a long‐lived species

Genovart

Oró

Tenan

2018

Ecology

View full text Add to dashboard Cite

Disentangling the influence of demographic parameters and the role of density dependence on species’ population dynamics is a challenge, especially when fractions of the population are unobservable. Additionally, due to the difficulty of gathering data at large spatial scales, most studies ignore the global dynamic of a species, which would integrate local heterogeneity dynamics and remove the noise of dispersal. We developed an integrated population model (IPM) at a global scale to disentangle the main demographic drivers of population dynamics in a long‐lived species. We used 28 yr of Audouin's Gull demographic data encompassing 69 local patches (comprising 90% of the world population). Importantly, we took into account the unobservable fraction of non‐breeders and also assessed the strength of density dependence for this fraction of the population. As predicted by life histories of long‐lived organisms, temporal random variation in survival was highest for immature individuals (1.326, 95% credible interval [CRI] 1.290–1.940) and lowest for adults (0.499, 95% CRI 0.487–0.720). Large temporal fluctuations in the probability of taking a reproductive sabbatical would partly explain the consistency in adult survival, with individuals most likely refraining from breeding when environmental conditions were harsh. Immature survival and fertility were the main drivers of population dynamics during the study period (r2 = 0.83, 0.77–0.87 and 0.73, 0.63–0.79, respectively). We found strong evidence of density dependence, not only due to the number of breeders (r2 = −0.34, −0.43 to −0.24) but also due to individuals on sabbatical (r2 = −0.18, −0.33 to −0.01). From a conservation point of view, the species shows a 5% annual global decrease during the last 10 years, and we propose an update of its conservation status. Even though population dynamics of long‐lived organisms are very sensitive to changes in adult survival, we show here that, in the absence of strong environmental perturbations affecting this vital rate, fluctuations in population density are mainly driven by variations in survival of immature individuals and fertility. Integrated models based on long‐term monitoring at a global scale may enhance our ecological and evolutionary understanding of how demographic drivers influence population dynamics.

show abstract

“…Horswill et al . ), and also permits density‐dependent processes to be applied through different combinations of demographic processes (e.g. Szostek, Schaub & Becker ).…”

Section: Synthesismentioning

confidence: 99%

Density dependence and marine bird populations: are wind farm assessments precautionary?

Horswill

O’Brien

Robinson

2016

Journal of Applied Ecology

View full text Add to dashboard Cite

Summary Although density‐dependent regulation of population growth is thought to be relatively widespread in nature, density‐independent models are often used to project the population response to drivers of change. Such models are often considered to provide a maximum estimate of mortality and therefore offer a precautionary approach to impact assessment. However, this perception assumes that density dependence operates as compensatory (negative density dependence), and overlooks that other forms of density dependence, such as depensation (positive density dependence), would generate a contrasting population response. Currently, there is debate about including density‐dependent mechanisms in models that assess the impact of offshore wind farms on marine bird populations. Density dependence is considered poorly understood for this group of species. Consequently, it is either excluded from assessments, or incorporated in a compensatory form that has little empirical validation. We reviewed the evidence for compensatory and depensatory regulation of 31 marine bird species, and conducted a meta‐analysis to examine the functional shape of density‐dependent population growth. The evidence was also evaluated in relation to established species‐specific indices of wind farm vulnerability in order to assess whether compensatory mechanisms are likely to offset losses associated with collision or displacement. Compensatory regulation was reported across all of the demographic processes and focal groups considered, and was attributed to a variety of causal mechanisms. The strength of compensatory population growth appeared consistent between colonies; however, the regulation of productivity was highly context‐dependent with a similar number of studies reporting compensatory, depensatory and insignificant effects. Depensation was consistently attributed to increased rates of predation at lower population densities. Synthesis and applications. We conclude that among marine bird species with high vulnerability to wind farms, compensatory regulation is unlikely to offset large and sustained losses from the breeding population. In addition, depensation has the potential to accelerate population declines and generate local or regional extinctions, especially in smaller colonial species. Consequently, density‐independent models will not offer a consistently precautionary approach for assessing the potential impact of wind farms on marine bird populations. Instead, assessments should examine the potential population response using a range of density‐dependent structures.

show abstract

Unravelling the relative roles of top‐down and bottom‐up forces driving population change in an oceanic predator

Cited by 40 publications

References 56 publications

Prey‐driven control of predator assemblages: zooplankton abundance drives aquatic beetle colonization

Prey‐driven control of predator assemblages: zooplankton abundance drives aquatic beetle colonization

Immature survival, fertility, and density dependence drive global population dynamics in a long‐lived species

Density dependence and marine bird populations: are wind farm assessments precautionary?

Contact Info

Product

Resources

About