Ecological traps: current evidence and future directions

Abstract

Ecological traps, which occur when animals mistakenly prefer habitats where their fitness is lower than in other available habitats following rapid environmental change, have important conservation and management implications. Empirical research has focused largely on assessing the behavioural effects of traps, by studying a small number of geographically close habitat patches. Traps, however, have also been defined in terms of their population-level effects (i.e. as preferred habitats of sufficiently low quality to cause population declines), and this is the scale most relevant for management. We systematically review the ecological traps literature to (i) describe the geographical and taxonomic distribution of efforts to study traps, (ii) examine how different traps vary in the strength of their effects on preference and fitness, (iii) evaluate the robustness of methods being used to identify traps, and (iv) determine whether the information required to assess the population-level consequences of traps has been considered. We use our results to discuss key knowledge gaps, propose improved methods to study traps, and highlight fruitful avenues for future research.

Keywords: effect size; fitness; habitat selection; human-induced rapid environmental change; maladaptive; preference.

Figure 1.

The (a) ecosystems (b) continents and (c) focal taxa where ecological traps have been demonstrated (D) and studied but not demonstrated (ND).

Figure 2.

Effect sizes (log response ratio) of differences in fitness (orange) and preference (red) between ecological traps and non-trap habitats (a) caused by different processes and (b) affecting different taxa. Mean (and standard error) effect sizes shown. The number in brackets on the y-axis indicates sample size.

Figure 3.

The relationship between the fitness costs of ecological traps and the preferences animals exhibit for them (both log response ratios). Zero values on the x-axis represent equal preference traps. Three potential effect sizes are shown for nine studies where no data on fitness reductions were present: a 10 times reduction in fitness in traps (solid black line), a 5 times reduction (dashed grey line) and a 20 times reduction (dashed black line)—see the methods section for further details. Linear regression models for each of these effect sizes and when these studies were removed all p < 0.01, R² > 0.50.

Figure 4.

Assessing if studies consider the patch-level characteristics required to assess the landscape-scale consequences of traps. Nine variables were scored (table 1; electronic supplementary material, table S1) in 127 studies across the four categories (indicated by colouring) likely to determine the severity of traps [10]. The proportion of studies that considered a particular variable is denoted for studies that demonstrated a trap on the y-axis (n = 29), and studies that did not demonstrate a trap on the x-axis (n = 98). The dotted line shows the 1 : 1 linear relationship to indicate when the two types of studies provide comparable information. The area above this curve indicates when studies that demonstrated a trap have considered a variable more frequently than studies that did not demonstrate a trap.