Review 21.9.2023 Diversity and Distribution

This study investigated how spatially variable stream insect traits are and how transferable trait-environment relationships are across large spatial scales. The study collected datasets of aquatic insects in five regions, i.e. Australia, Europe, North America, New Zealand, and Southern Africa, from eight publications. The authors identified traits that are important in separating trait profile groups (TPGs) and assessed if variability between TPGs was associated with climatic variability within each region. The study is potentially important in biodiversity conservation, especially in the conservation of aquatic insects that have been ignored by ecologists. The idea of the study is novel, but there are a few issues in the manuscript that the authors should deal with, before the manuscript is considered for publication. Also, I suggest the authors send the manuscript for language checking by an English native speaker.

Introduction
Some paragraphs in the Introduction lack references. The authors should cite relevant literature to support the statements.

The authors should give clear definitions to ‘trait profiles’ and ‘trait profile groups’ in the Introduction, as they are the terms most frequently used in this manuscript.

It would be nice to write more about stream insects after describing stream invertebrates, as the datasets are on aquatic insects, instead of general aquatic invertebrates.

Methods & Materials
The section is quite well described and supported with sufficient supplementary materials. The stream insect trait data were collected from eight different publications. I have two concerns regarding the datasets. First, how did the authors select the datasets/publications among many published datasets and papers? Second, did the eight papers cited here apply the same method to collect aquatic insects? If they did, the authors should mention what method the eight papers utilized to collect aquatic insects. If not, the authors should justify how they tried to avoid biases in aquatic insect assemblages caused by different sampling methods in the publications.

Results
The section is quite well described and supported with many figures and tables in supplements.

Discussion
The authors should try to explain the observed phenomena in this paper after comparing the results with previous studies. For example, Page 27 Lines 53 – 57 to Page 28 Lines 3: “Their most grouping features were body size, … … where feeding mode, respiration, body size, and locomotion traits were among the most important traits in most regions.” The authors should explain why these traits are important, after comparing the results of other studies.

The authors could write about implications in the context of current global change and address the points found in this study and how they should be integrated into management decisions.

Minor comments:
Page 3 Line 21: Give an example of anthropogenic stressors that are relevant to this study.

Page 3 Lines 24 – 31: Cite literature to support the statements.

Page 4 Lines 7 – 31: Cite literature to support the statements.

Page 5 Lines 32 – 50: I suggest the authors rephrase the expectations into hypotheses and number the hypotheses.

Page 25 Lines 36 – 44: A very long sentence. I suggest the authors cut it into short sentences. A sentence is better not to go over three lines.

Page 26 Lines 24 – 33: A very long sentence.

Figure 1: Is it possible to draw the hulls with thicker lines? Plot the points with different shapes and colours on the top of the hulls. The current figure is not very clear.