Haeckel, Ernst (1866). Generelle Morphologie der Organismen [The General Morphology of Organisms] (in German). Vol. 2. Berlin, (Germany): Georg Reimer. From p. 286: "Unter Oecologie verstehen wir die gesammte Wissenschaft von den Beziehungen des Organismus zur umgebenden Aussenwelt, wohin wir im weiteren Sinne alle "Existenz-Bedingungen" rechnen können." (By "ecology" we understand the comprehensive science of the relationships of the organism to its surrounding environment, where we can include, in the broader sense, all "conditions of existence".)
Smith, Christopher C. (September 1988). "Elements of Ecology Robert Leo Smith". The American Biology Teacher. 50 (6): 394. doi:10.2307/4448774. ISSN0002-7685. JSTOR4448774.
Nieder, J., Prosperí, J. & Michaloud, G. Epiphytes and their contribution to canopy diversity. Plant Ecology 153, 51–63 (2001). https://doi.org/10.1023/A:1017517119305
Lloyd, David G.; Schoen, Daniel J. (1992). "Self- and Cross-Fertilization in Plants. I. Functional Dimensions". International Journal of Plant Sciences. 153 (3, Part 1): 358–369. doi:10.1086/297040. S2CID85344103.
Smith, Christopher C. (September 1988). "Elements of Ecology Robert Leo Smith". The American Biology Teacher. 50 (6): 394. doi:10.2307/4448774. ISSN0002-7685. JSTOR4448774.
Lloyd, David G.; Schoen, Daniel J. (1992). "Self- and Cross-Fertilization in Plants. I. Functional Dimensions". International Journal of Plant Sciences. 153 (3, Part 1): 358–369. doi:10.1086/297040. S2CID85344103.
Smith, Christopher C. (September 1988). "Elements of Ecology Robert Leo Smith". The American Biology Teacher. 50 (6): 394. doi:10.2307/4448774. ISSN0002-7685. JSTOR4448774.