What the heck is habitat?

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Adam Janke | Assistant Professor in Natural Resource Ecology and Management and Extension Wildlife Specialist, Iowa State University

I have seen a wide gamut of responses to the question posed in the title of this post. While preparing for my Ph.D. candidacy exams, I was asked a version of this question as it related to ducks and agonized over the response for months (you’ll see elements of my answer below). In another extreme, I recently posed the same question at a meeting and received an enthusiastic, unequivocating answer of, “corn fields.” I’ll spare you the details of why it is that Iowa’s 13.2 million acres of corn are almost certainly not a limiting feature for ducks, but suffice it to say that my mental picture of habitat for ducks (wetlands) was starkly different from this respondent’s own mental image (corn fields). Same word. Same question. Drastically different responses.

The mental image we conjure of “habitat” depends on two factors:

The first factor, is what kind of habitat we’re talking about. Habitat the noun is functionally meaningless without the clarifying help of one or more adjectives like “pileated woodpecker habitat”, “duck nesting habitat” or “winter pheasant habitat”. Asserting, “I’m creating habitat” could simultaneously mean you’re building a flat-roofed building where Common Nighthawks will nest or you’re restoring the Regal Fritillary butterfly and it’s host plants to a native prairie. Same word. Drastically different meanings.

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What “habitat” means varies widely between species, like mallards (left) who make use of a diversity of wetlands, ponds, and fields, and pileated woodpeckers (right) who are picky in their selection of large tracts of mature forests. (Photos by Adam Janke and Pixabay )

The second factor, is the one that gave me so much anxiety in anticipation of the question during my candidacy exams. That is, what features of habitat are most limiting for a species of wildlife, and how do we know? Biologists are taught to remember Leibig’s Law of the Minimum. Without information on how limiting any one resource is, we’re left only guessing and often fail to see desired responses to habitat restoration that miss the mark on limiting factors. To uncover limiting factors we must take measurements, which presents its own challenges because wildlife are hard to observe (hence the ‘wild’ part). Volumes in my professional discipline are written on the issue of “imperfect detectability” and overcoming this observational challenge is the source of substantial frustration.

Thus, to answer “what the heck is habitat” in Iowa, or any landscape, we need to make some assumptions. Leading to the chronically unsatisfying assertion — “it depends” — as the prevailing answer to the question.

However, I think it safe to make a few generalizations to answer this question. To do so, I’m going to lean on the collective expert opinion of 74 of my peers that recently responded to a survey I sent to attendees of the annual Iowa Habitat Partners Conference (two of those attendees and conference organizers are featured on this month’s episode of The Conservation Chat). These 74 wildlife biologists from across the state were asked to rank “the ‘quality’ [of each practice] as habitat for pheasants, quail, and other farmland wildlife in Iowa.” I standardized each participant’s response so that each ranking ranged from 0, the lowest habitat quality score, to 100, the highest.

HabitatSurveyResults1-2019

Mean (± standard deviation) ‘habitat quality’ ratings from 74 wildlife biologists in Iowa asked to rank the quality of each habitat type for ‘pheasants, quail, and other farmland wildlife.’

Here’s the generalizations that emerged:

  • Any changes to the status quo are improvements in habitat quality for farmland wildlife. 93% of respondents gave corn-bean rotations or continuously grazed pastures their lowest habitat quality score.
  • Natural, perennial features like wetlands, prairies, and rotational pastures are higher quality.
  • Diversity in plants and vegetation structure matter, as reflected by the negative attitude of the group towards ‘Non-diverse’ CRP fields and continuously grazed pastures.
  • Larger patches of vegetation rate higher than smaller ones, as reflected in the higher ratings of whole-field CRP fields, wildlife areas, and wetlands, over small patches like stream buffers, prairie strips, and ‘odd areas.’

Beyond these generalizations, the wide range in respondent rankings clearly conveyed little consensus on the quality of individual features in the absence of additional clarifying details on the species or places in question. Here we find the final point of consensus.

Immediately after I hit “send” on the survey, a chorus of cries of “it depends” and “this isn’t fair!” came echoing back to my inbox from every corner of the state. Biologists, trained to think critically about limiting factors, plant diversity, patch size and connectivity, and a whole suite of other factors determining the ‘quality’ of any given ‘habitat’, insisted on answers to questions like “What factors are already limiting”, “What species”, “What part of the state” and so on in their emails.

I smiled receiving these emails because this skepticism, intuition, and critical thinking about what the heck is habitat is exactly as it should be.

Adam Janke