Understanding ecosystems as complex systems requires learners to explain ecological phenomena by reasoning about indirect relationships and multi-step causal connections rather than relying solely on direct cause–effect explanations (Mehren et al., 2018; Mambrey et al., 2022). Research on science education has consistently demonstrated that middle school students tend to interpret food webs through monocausal or linear reasoning patterns, which limits their ability to recognize indirect effects and feedback-based population dynamics (Hogan, 2000; Grotzer & Basca, 2003; Hokayem & Gotwals, 2016). Such reasoning patterns often result in static and hierarchical conceptions of ecosystems, where interactions are reduced to isolated predator–prey relationships instead of dynamic system-level processes (Webb & Boltt, 1990; Griffiths & Grant, 1985). Reasoning about indirect ecological relationships, is closely associated with system modeling skills, as learners are expected to trace causal influences across multiple system components and trophic levels (Mehren et al., 2018; Ben-Zvi Assaraf & Orion, 2010). Mehren (2018) and Mambrey et al.(2020 ) state that system modeling probe students’ ability to reason about indirect, multi-step, and cross-level relationships, such as how a change in one species could affect another species that is not directly connected in the same food chain.Previous studies have emphasized that the ability to model indirect effects represents a critical threshold in the development of advanced systems thinking, marking a transition from localized explanations toward holistic understandings of ecosystem dynamics (Grotzer & Solis, 2015; Mambrey et al., 2020). Empirical evidence, however, suggests that many students struggle to construct such multi-step causal models, particularly when feedback mechanisms and non-adjacent interactions are involved (Hogan, 2000; Hokayem & Gotwals, 2016; Hokayem, Ma, & Jin 2015; Mambrey et al., 2022).

Based on this theoretical background, the present study focuses on students’ reasoning about indirect relationships within a single ecological system, namely a meadow food web, as a context for examining system modeling skills (Mehren et al., 2018; Mambrey et al., 2020; 2022; Sweeny & Sterman, 2007 ). In line with this focus, the study addresses the following research question: To what extent are students able to reason about indirect relationships within a single individual system (the meadow food web) and model multi-step causal connections?

It should be underlined here that the meadow food web diagram used in the study includes daisies as producers, caterpillars and snails as primary consumers, birds and mice as secondary consumers, and foxes as the top predator, with energy input provided by the sun. Although a directed feeding arrow from snails to birds is represented in the diagram, this depiction requires students not merely to identify a single-step relationship but to model indirect causal connections by considering multiple trophic pathways and system-level interactions within the food web (Mambrey et al., 2020).

This study employed a descriptive quantitative research survey design to examine students’ systems thinking skills, with a particular focus on their ability to reason about indirect relationships and to model multi-step causal connections within a single ecological system. Data were collected from 510 students enrolled in the 6th, 7th, and 8th grades in different public schools using a questionnaire developed by Mambrey and her colleagues (2020; 2022) which is grounded in the systems thinking framework proposed by Mehren et al. (2018). It is embedded in a meadow food web and is designed to assess students’ reasoning about population-level changes, indirect effects, and causal relationships across multiple system components. The questionnaire includes items targeting different dimensions of systems thinking, namely system organization, system behavior, system-consistent action intention, and system modeling skills. The study reports findings related only to system modeling skills; therefore, focuses on students’ ability to recognize indirect and feedback-based relationships and to mentally model multi-step causal chains involving multiple trophic levels within the same food web (Mambrey, Timm, et al. 2020). Students’ responses were analyzed through a three-stage analytical procedure grounded in the systems thinking and causal reasoning frameworks (Mehren et al., 2018). This integrated analytical approach provided a detailed and systematic examination of students’ ability to reason about indirect ecological relationships and to model multi-step causal connections within a single ecological system. In the first stage (Stage 1), students’ answer choices for each item were examined descriptively to identify how learners reasoned about indirect population-level interactions and multi-step causal connections within the meadow food web. In the second stage (Stage 2), students’ responses across the indirect relationship items were examined in terms of causal reasoning patterns. Based on the structure of the implied explanations, responses were classified as monocausal, linear, or complex, enabling an examination of the overall distribution of reasoning patterns. In the Stage 3, a more fine-grained analysis was conducted by coding students’ responses according to the causal reasoning framework proposed by Mehren et al. (2018). Prior to conducting the study, ethical clearance was granted from the University’s Human Research Ethics Committee and the Ministry of National Education.

The study revealed that students performed relatively better in identifying indirect relationships involving short and conceptually accessible causal chains. For example, in a question requiring students to recognize an indirect relationship between snails and birds, most students demonstrated complex reasoning (Stage 3) by identifying the role of shared interactions within the food web. Fewer than thirty percent reported that snails and birds were too far apart to influence one another, while only small portion denied any influence believing that organisms were not part of the same chain. These responses reflect monocausal reasoning (Stage 1) emphasizing proximity or direct interaction rather than systemic connections. When asked ‘how the population of caterpillars could be increased in the food web’, more than half of the students, indicated that “the population of caterpillars could be increased by increasing the number of daisies,” showing complex reasoning (Stage 3). These students seemed aware of increasing the number of daisies could indirectly increase the caterpillar population. However, when a question requiring students to trace a longer and more complex causal chain involving snails, mice, and foxes was posed, the percentages of students exhibiting complex reasoning decreased. As an example, when asked ‘how can the number of foxes in the food web be reduced in a given food web’, only 42% agreed that “one could reduce the number of snails, because then foxes could feed on fewer mice.” Some students argued that “reducing the number of snails would decrease the population of all organisms in the food web’. Others alluded that “the fox population cannot be reduced by changing the population of organisms that are not directly connected to foxes”. Still others claimed that “the number of foxes cannot be reduced because foxes are at the top of the food web,” which reveals a misconception, the belief that top predators remain unaffected by changes at lower trophic levels.

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