Direct evidence that density-dependent regulation underpins the temporal stability of abundant species in a diverse animal community

To understand how ecosystems are structured and stabilized, and to identify when communities are at risk of damage or collapse, we need to know how the abundances of the taxa in the entire assemblage vary over ecologically meaningful timescales. Here, we present an analysis of species temporal variability within a single large vertebrate community. Using an exceptionally complete 33-year monthly time series following the dynamics of 81 species of fishes, we show that the most abundant species are least variable in terms of temporal biomass, because they are under density-dependent (negative feedback) regulation. At the other extreme, a relatively large number of low abundance transient species exhibit the greatest population variability. The high stability of the consistently common high abundance species—a result of density-dependence—is reflected in the observation that they consistently represent over 98% of total fish biomass. This leads to steady ecosystem nutrient and energy flux irrespective of the changes in species number and abundance among the large number of low abundance transient species. While the density-dependence of the core species ensures stability under the existing environmental regime, the pool of transient species may support long-term stability by replacing core species should environmental conditions change.

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Density dependence in an experimental boreal forest understory community

Botany ◽

10.1139/b10-048 ◽

2010 ◽

Vol 88 (8) ◽

pp. 753-764 ◽

Cited By ~ 3

Author(s):

Michael A. Treberg ◽

Roy Turkington

Keyword(s):

Boreal Forest ◽

Density Dependence ◽

Abiotic Factors ◽

Life Stage ◽

Plant Competition ◽

Biotic Interactions ◽

Abundant Species ◽

Forest Understory ◽

Density Dependent ◽

Shoot Mass

Density-dependent regulation in plants may occur at the level of the entire community and may differ in magnitude and direction at different life history stages such as germination, survival and growth, and under different abiotic conditions. We constructed semi-natural communities of boreal forest understory species planting 10 of the most abundant species. The experimental communities were established from seed or from cuttings and grown in sandboxes at six densities that extended far above and below average natural field density, while maintaining constant relative species proportions (a community density series (CDS)). We used two watering and fertilization levels in a factorial design. At the community level, both emergence and final per-plant shoot mass were negatively density dependent, while survival to the end of the season was facilitative. The effect of water was positive at seed emergence, whereas fertilizer negatively affected survival. Species-specific responses were also dependent on life stage. We demonstrated that density dependence is important in structuring this unproductive boreal understory habitat. The CDS approach allows us to quantify the effects of plant competition at the community and species levels, and to determine whether the importance of these biotic interactions depend on abiotic factors.

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Evolution of positive and negative density-dependent dispersal

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2014.1226 ◽

2014 ◽

Vol 281 (1791) ◽

pp. 20141226 ◽

Cited By ~ 29

Author(s):

António M. M. Rodrigues ◽

Rufus A. Johnstone

Keyword(s):

Density Dependence ◽

Habitat Heterogeneity ◽

Temporal Stability ◽

Ecological Factors ◽

Positive Density ◽

Density Dependent ◽

High Dispersal ◽

Variable Environments ◽

Negative Density Dependence ◽

Density Dependent Dispersal

Understanding the evolution of density-dependent dispersal strategies has been a major challenge for evolutionary ecologists. Some existing models suggest that selection should favour positive and others negative density-dependence in dispersal. Here, we develop a general model that shows how and why selection may shift from positive to negative density-dependence in response to key ecological factors, in particular the temporal stability of the environment. We find that in temporally stable environments, particularly with low dispersal costs and large group sizes, habitat heterogeneity selects for negative density-dependent dispersal, whereas in temporally variable environments, particularly with high dispersal costs and small group sizes, habitat heterogeneity selects for positive density-dependent dispersal. This shift reflects the changing balance between the greater competition for breeding opportunities in more productive patches, versus the greater long-term value of offspring that establish themselves there, the latter being very sensitive to the temporal stability of the environment. In general, dispersal of individuals out of low-density patches is much more sensitive to habitat heterogeneity than is dispersal out of high-density patches.

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